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FINAL REPORT SUBMITTED BY Dr. FRANK E. INSCORE DECEMBER 18, 2002. POSTDOCTORAL RESEARCH ASSOCIATE IN ENEMARK RESEARCH GROUP THE UNIVERSITY OF ARIZONA, DEPARTMENT OF CHEMISTRY SUMMARIZING AND POINTING OUT KEY SYNTHETIC ASPECTS ON SYSTEMS STUDIED

MAY 2000 TO DECEMBER 2002

This report focuses on the 4 major high-valent TM dithiolate (and thiolate) systems that were studied as a postdoctoral fellow for JHE. These include 1). Tp*ME(S-S), where M=Mo: E=O,S,NO and M=W: E=O; 2). [MoO(S-S)2]-; 3). Tp*MoO2SR; and 4). Cp2M(S-S), where M = Mo, W. The following report, which is far from being complete, is an attempt to bring closure to the study of these systems regarding my contributions and purpose. The goals and objectives of these studies and interest are an extension and continuation of ideas/postulates initially developed from my PhD work as a spectroscopist, and here as well, which has provided the motivation to balance out my knowledge of these systems by obtaining extensive synthetic experience. Thus, this report primarily serves to present key synthetic aspects and methodologies developed that are described in some detail for specific examples, and therefore should provide additional assistance to others interested in the syntheses, chemistry and the structural, electronic and electrochemical properties of these systems. The majority of the spectroscopic sampling I have left for others in the group, thereby coupling them into the research and providing projects and material for their theses and dissertations. In addition, I have made it a point to also couple as much as possible others in the group into these synthetic aspects so they can obtain valuable experience and balance, and thus independence in their future works. I have therefore included in the report praise and credit to those involved and their specific contributions to these previous and on going studies. It has certainly been an honor and valuable learning experience to serve as a senior research associate in the NIH funded world class group of Prof. John H. Enemark. Special praise and professional respect go to Julien Schirilin , Pablo Bernardson (both undergraduates) and Hemant Joshi (graduate student), all of whom I have had the honor of directing and participating in their research here at the University of Arizona (Dept of Chem), as well as my wife (Kristie) who put up with my long and sometimes weird hours. The most praise goes to John Enemark, who allowed me the freedom and independence to develop my own projects of interest, which have resulted in papers published and new ideas that has motivated others in the group to pursue further.

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Works past, in progress, contributions and future responsibilities w/r to model studies. Synthetic Systems from May 2000 to December 2002. FeTTP Porphirin complex (with Hiroshi) for EPR std for Arnold. KTp* Ultra pure H2bdt (white crystals) from vac.distil.under Ar from H2bdt from Na2bdt/from protected form and/or Li2bdt from S8/ HSPh(vac distilled under Ar) ; using reported synthetic methods. Na2bdt from H2bdt/NaOMe/MeOH; H2bdt being commercial or synthesized. Note one can also use Na(K). similarly NaSPh from HSPh/Na2EDT from H2EDT/Na2PDT from H2PDT using commercial dithiols (Com.dithiols, that are liquids at RTcan also and easily be distilled under vac/Ar, e.g H2bdt,EDT, HSPH) H2qdt/ /Na2qdt/H2qdt from reported synthetic method. MoO(Cl)3THF2 from purified: MoCl5 (Aldrich)+THF// WO(Cl)3THF2 from purified: WCl6 (Aldrich)+THF (Tp*)MoOCl2 // Other potential precursors as reported: (Tp*)MoO(OMe)2, (Tp*)MoO(OEt)2, (Tp*)MoO(EDO) (Tp*)MoO(bdo), (Tp*)MoO(bdo,s), (Tp*)MoO(OPh)2 (Tp*)MoO(SPhMe)2 (Tp*)MoO(tdt), (Tp*)MoO(bdt), (Tp*)MoO(bdtCl2) (Tp*),MoO(qdt), (Tp*)MoO(edt) (Tp*)MoO(EDT), (Tp*)MoO(EDTMe2), (Tp*)MoO(PDT) (Tp*)MoSCl2 from (Tp*)MoOCl2 (Tp*)MoS(tdt), (Tp*)MoS(bdt) (Tp*)WOCl2 (Tp*)Mo(CO)3 from Mo(CO)6 (Aldrich) // (Tp*)W(CO)3 from W(CO)6 (Aldrich) (Tp*)MoNO(CO)2 (Tp*)MoNOI2 // (Tp*)MoNO(OEt)2/ “ (Tp*)MoNO(EDO)” “semi-isolated/ and identified by MS” (Tp*)MoNO(tdt) (Tp*)MoNO(bdt) (Tp*)MoNO(bdtCl2) “(Tp*)MoNO(qdt)” “identified in crude react. mixture by MS, very unstable for separating on collumn” (Tp*)WO(CO)2 // (Tp*)WI(CO)2 (Tp*)WOI2 (Tp*)WO(bdt) (Tp*)WO(tdt) [MoO(CL)4]- from MoCl5 (Aldrich) // [MoO(Cl)4H2O]- [MoO(SPh)4]- from HSPh and MoOCL3THF2 // [MoO(SPhCl)4]- from HSPhCl and MoOCL3THF2 [MoO(EDT)2]- [MoO(bdt)2]- [MoO(bdtCl2)2]- “[MoO(SPh)2(bdtCl2)]-“ “unstable intermediate semi-isolated and identified from MS” Mo2O2Cl2 from // Mo2O2Br2 from// (Tp*)MoO2Cl // (Tp*)MoO2Br// (Tp*)MoO2SPh (Tp*)MoO2SCH2Ph Cp2MoCl2 (Aldrich)/Cp2WCl2 (Aldrich) Cp2Mo(tdt), Cp2Mo(bdt), Cp2Mo(bdtCl2), Cp2Mo(qdt), Cp2Mo(edt) from Cp2MoCl2 “CpMo(bdt)]2-“ “unexpected side product isolated/ identified by MS” Direct synth from CpMo(CO)3I too. Cp2W(bdt), Cp2W(bdtCl2) from Cp2WCl2

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(Tp*)MoVO(Cl)2

KTp*

W(CO)6

(Tp*)MoVO(edt)

(Tp*)MoVO(bdt)

(Tp*)MoVO(qdt)

(Tp*)MoVO(bdtCl2 )

(Tp*)MoVO(tdt)

(Tp*)MoNO(CO)2

(Tp*)MoIINO(Cl)2

(Tp*)MoIINO (S-S)

(Tp*)MoIINO(I)2

(Tp*)MoIINO(OEt)2

(Tp*)MoIINO(OMe)2

Na2(S-S)H2(S-S)2:NEt3

Na2(S,S)2:NEt3H2(S,S)

H2(S-S)

Mo(CO)6

(Tp*)WVO(Cl)2

(Tp*)WVO(S-S)

(Tp*)WVO(I)2

Na2(S-S)H2(S-S)2:NEt3

Na2(S,S)2:NEt3H2(S,S)

2Na(OR)2Na(SR)

(Tp*)WVO(SR)2

(Tp*)WVO(OR)2

WOCl3THF2

Mo(Cl)5 W(Cl)6

MoOCl3THF2

(Tp*)MoVO(S-S)

Na2(S,S)2:NEt3H2(S,S)

(Tp*)MoVO(I)2

(Tp*)MoVO(EDO)

(Tp*)MoVO(OR)2

(Tp*)Mo(CO)2(Tp*)W(CO)2

(Tp*)MoVS(Cl)2

(Tp*)MoVS(S-S)

Na2(S,S)2:NEt3H2(S,S)

(Tp*)MoIINO(bdt)

“(Tp*)MoIINO(qdt)”

(Tp*)MoIINO(bdtCl2 )

(Tp*)MoIINO(tdt)

(Tp*)MoVS(bdt)

(Tp*)MoVS(tdt)

(Tp*)WVO(bdt)

(Tp*)WVO(tdt)

(Tp*)MoVO(SPhMe)2

(Tp*)MoVO(EDT)(Tp*)MoVO(EDTMe2)

(Tp*)MoVO(bdo)

(Tp*)MoVO(EDO)

(Tp*)MoVO(PDT)

(Tp*)MoVO(OPh)2(Tp*)MoVO(OMe)2

(Tp*)MoVS(Cl)2(Tp*)MoIINO(I)2(Tp*)MoVO(Cl)2(Tp*)WVO(I)2(Tp*)WVO(Cl)2

(Tp*)MoVO(bdo,s)

“(Tp*)MoIINO(EDO)”

KTp*

MoOCl3THF2WOCl3THF2(Tp*)MoNO(CO)2

Na2(edt)Na2(bdt)

H2(edt)

H2(bdt)

Aldrich H2(tdt)

Na2(qdt) H2(qdt)

H2(bdt) H2(bdtCl2)

(Tp*)MoVIO2(Cl)

(Tp*)MoVIO2(Br)(Tp*)MoVIO2(SPh)

(Tp*)MoVIO2(SCH2Ph)

MoCl5 MoOCl3THF2

[MoO(SPh)4]-

[MoO(SPhCl)4]-

[MoO(EDT)2]-

[MoO(bdt)2]-

[MoO(bdtCl2)2]-

[MoO(Cl)4]-

Cp2 MoIVCl2

Cp2 WIVCl2

Cp2 MoIV(bdt)

Cp2 MoIV(tdt)Cp2 MoIV(bdtCl2)Cp2 MoIV(qdt)

Cp2 MoIV(edt)

[CpMoIV(bdt)2]-

Cp2 WIV(bdt)

Cp2 WIV(bdtCl2)

Benz// 2Net3// H2O reflux 1hr

Benz// H2O reflux 1hr

H2(S-S)

Na2(edt)

Benz// Net3// H2O reflux 1hr

H2(S-S)

H2(S-S)

rt

4H(SPhR)

4Net3

THF(excess)

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(Tp*)MoVO(edt)

(Tp*)MoVO(bdt)

(Tp*)MoVO(qdt)

(Tp*)MoVO(bdtCl2)

(Tp*)MoVO(tdt)

(Tp*)MoIINO(bdt)

(Tp*)MoIINO(bdtCl2)

(Tp*)MoIINO(tdt)

(Tp*)MoVS(bdt)

(Tp*)MoVS(tdt)

(Tp*)WVO(bdt)

(Tp*)WVO(tdt)

•(Tp*)MoVO(SPhMe)2 chelate effects:monodentate vs bidentate (Tp*)MoO(S2) systems

•(Tp*)MoVO(EDT) saturation effects: SC-CS vs SC=CS; compare to edt complex. (Tp*)MoVO(EDTMe2) compare to edtMe2 complex, in case cant make edt complex.

•(Tp*)MoVO(bdo) donor atom type effects (O vs S)

(Tp*)MoVO(EDO)

•(Tp*)MoVO(PDT) chelate ring size effects

(Tp*)MoVO(OPh)2 donor atom effects.

(Tp*)MoVO(OMe)2

(Tp*)MoVS(Cl)2(Tp*)MoIINO(I)2(Tp*)MoVO(Cl)2(Tp*)WVO(Cl)2

(Tp*)MoVO(bdo,s) donor atom type effects (1O vs 1S)

(Tp*)WVO(I)2

(Tp*)ME(S-S) Precursors// Potential (Tp*)MO(S-S) Precursors

Submitted for:-Studies char prod identity/purity//chemical//physical properties//eval syn/pur route.-CV studies in DCE,identical conds. comparison; red/ox pots, rev, behavior ect.-Hetrogenous ET rates-structural studies/ comparison (XRD)-electronic studies/ comparison (IR(KBr-DCM)//EA(DCE)//EPR(Tol)//)-PES(GP-HeI/II) (NeI) studies/ comparison -rR(solid-solution(Ben)) vibrational studies/ comparison-DFT comp studies for structurally defined complexes;MO descript/basis elec struct. -Generation-isolation of 1e- red/ox species; parallel studies-struct-elec char of/comp.

Cp2 MoIV(bdt)

Cp2 MoIV(tdt)

Cp2WIV(bdtCl2)

Cp2 MoIV(qdt)

Cp2 MoIV(edt)

Cp2 WIV(bdt)

Cp2MoIV(bdtCl2)

(Cp2 MoIVCl2) (Cp2 WIVCl2) [MoO(SPh)4]-

•[MoO(SPhCl)4]-

•[MoO(EDT)2]-

[MoO(bdt)2]-

[MoO(bdtCl2)2]-

•[MoO(Cl)4]-

(Tp*)MoVIO2(Cl)

•(Tp*)MoVIO2(SPh)

•(Tp*)MoVIO2(SCH2Ph)

•[MoO(SPh)4]-

-IR/EA-Anionic PES

-DFT calcs

-CV

-XRD-IR/EA

-rR-DFT

Char;(MS/NMR)-CV

-XRD-IR/EA-PES (HeI/II)

-DFT

(Tp*)MoVIO2(Br)

DITHIOLATE COMPLEXES (with (-SC-CS-)n n=1,2; (-SCCCS-))

MS MS/NMRReactivity studies

THIOLATE COMPLEXES (with (-SR)n n=1,2,4)

ADDITIONAL COMPLEXES

(Tp*)MoVO(EDO)

These were also synthesized for comparison with potential Tp*MoNO analogs.Sent to Kirk group for additional vibrational database etc.

(Tp*)MoIINO(OEt)2

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I.Complexes of the{(Tp*)MoO}2+ System Type A.Preparation of Ligands 1. KTp* -There was some of this ligand already availlable in the lab; synthesized and commercial grade. Also, precursors for making this ligand were also availlable in the lab. -However, as this is the Enemark group and we specialize in stabilizing a wide variety of complexes with this ligand, KTp* was also freshly prepared and purified by following well established procedures as reported and further developed in this lab. This provides a better feel for the chemistry of this ligand, its properties, behavior and how to obtain in ultra pure form and handle, subsequent to using in various stages of reactions that ultimately involve metallation with Mo (W) forming 6-coordinatecomplexes. NOTE: -There is literature precedent for making Na salts of Tp*, and appears to change the reactivity somewhat vs KTp*, this was thought about but never got around to trying. Mike Arven (grad.stud) has taken my suggestion and is making both salts in his attempt to further stabilize a reaction route to making the (Tp’)MoOCl2 precursor with Tp’=Tp(F) vs Tp(Me) = Tp*. -It is apparent that the e- donating capabilities of the remote substituents on the Pz rings has a direct impact on the e- density of the metal and hence electronic structure as evident by the literature of various Tp’M complexes (w/r to structure; Tp’, Tp’-M, and M-L metrics, also different electronic and redox properties). The Lit needs to be scoured as there are a substantial number of papers with Tp’M that look at the effects or

(Tp*)MoVO(Cl)2

(Tp*)MoVO(S-S)

(Tp*)MoVO(edt)

(Tp*)MoVO(bdt)

+H2(bdo)

Na2(S-S)

H2(S-S)

-2 NaCl

2:NEt3

-2 Cl- H+:NEt3

MeOH

Tol

(Tp*)MoVO(OMe)2

(Tp*)MoVO(OR)2

(Tp*)MoO(O-O)

(Tp*)MoVO(EDO)

Na2(O-O)

H2(O-O)

2NaOR(2KOR)

2HOR

2NEt3

MeOH

Tol

Tol

Tol

Tol

Alc/solvl

2:NEt3

Na2(S-S)

H2(S-S)(Tp*)MoVO(S-S) ?

2NEt3?

Tol

TolSolv?

Solv?

(Tp*)MoVO(bdt)

(Tp*)MoVO(bdt)

(Tp*)MoVO(OEt)2

H2(S-S)

(Tp*)MoVO(bdt)

Tol

-H2(EDO)

(Tp*)MoVO(bdt)

(Tp*)MoVO(edt)

(Tp*)MoVO(qdt)

(Tp*)MoVO(bdtCl2 )

(Tp*)MoVO(tdt)

Na2(edt)Na2(bdt)

H2(edt)

H2(bdt)

AldrichH2(tdt)

H2(bdtCl2)

Na2(qdt) H2(qdt)

(Li2(bdt)//K2(bdt))

MoCl5

MoOCl3THF2

KTp* Mo(CO)6

(Tp*)MoVO(I)2

2:NEt3H2(S-S)Na2(S-S)(Tp*)MoVO(S-S) ?

Aldrich

2NaOMe /MeOH

H2(bdt)

-2 NaCl

Solv?

Solv?

2NaOMe

Tol

70°C

Tol

(Tp*)MoVO(edt)

(Tp*)MoVO(edt)

(Tp*)MoVO(edt)

(Tp*)MoVO(S-S) ?

(Tol?)

(Tp*)MoO(bdo)

Ligand Exchange:at elevated T(>rt)in np Solv Tol(Ben)

K2(S-S)

Tol

(Tp*)MoVO(EDT) //(SC-CS)-2 KClTol(Ben)

(Tp*)MoVO(SR)22HSR/NEt3

2NaSR/(KSR)

?

?

?

?

-2 I- H+:NEt3

-2 NaI

-2NaClTol

-2 Cl- H+:NEt3

-2 NaCl

-2H(OMe)

-2NaOMe

Tol(Ben)

Tol(Ben)

??

?

(Tp*)MoVO(mnt)Na2(mnt) H2(mnt)

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report the effects of Tp’ =H,Me,F, and other such variations etc in an isostructural environment w/r to the metal and other coordinated ligands. This is important as the question now to address is how the Tp ligand and the nature of it affects the electronic structure of Tp’ME(S-S) complexes, as we have now probed the effects of the metal, axial changes, and nature of the equatorial (dithiolate) ligand with Tp’(=Tp*) remaining invariant. Furthermore, changing from Tp(Me) to Tp(F) with its expected different e- donating ability (due to e- withdrawing property of F substituents) is anticipated to shift Tp ionizations in PES and may deconvolute S based ionizations lying under the envelope in the Tp* systems aiding in band assignments. Mike is attempting to address these issues as directed by JHE. --Mike and I on our 1st attempt to make Tp(F)MoOCl2 witnessed firsthand the difference that the nature of Tp’ has on making this precursor, and hence reflecting the reactivity/stability of the KTp’ ligand. This is not an easy problem or syntheses, but I believe it can be done with perseverence. HeI(II?)PES (Hemant) of KTp(F) showed significant shifts in the ionizations vs KTp(Me) consistent with e- withdrawing nature of F and also consistent with Mikes calc shifts in energy with this substitution. The goal here was to make the halide precursor and subsequent ligand exchange for preparing Tp(F)MoO(bdt) and comparing to the previous well characterized Tp(Me)MoO(bdt). This should significantly change the electronic structure (and metrics) such that would help in elucidating the PES of the Tp*MoO(S-S) complexes. The differences in the Tp(F) ligand valence MO energies and e- withdrawing properties, upon interacting with the metal should have an affect on the electronic structure of the Mo complex, and more importantly shift the Tp’ ionizations in PES so that can resolve out additional L bands. Side Note: w/r to above applications, problems with initial synthesis may be due to presence of water in KTp(F), I have suggested this as possible reason for decomposition for various reasons (e.g. hydrolysis of precursor) and it is evident that the initial salt was wet. Mike is trying ways to eliminate any water from KTp’ prep. Mike may also consider utilizing a different precursor other than Tp’MoOCl2, e.g. such as the Tp’ analog of (Tp*)MoOI2, the latter has been made/reported in the literature but yet to be isolated in our lab or even known whether it will undergo ligand exchange. Whether this would work or not for Mike remains to be seen. -In fact the use of (Tp*)MoOI2 as an alternative precursor for the target dithiolate complexes afforded by the di-Cl analog in this particular system has yet to be applied. I have suggested the use of (Tp*)MoOI2 as a potential precursor for ligand exchange reactions to make Tp*MoO(S-S) based on our success for employing this type of precursor (Tp*)MEI2 (M=W,E=O; M=Mo, E=NO) in making the corresponding dithiolene complexes, whereas the Cl analogue in these latter systems could be isolated it did not affect the desired reaction. The use of this complex as a potential precursor is certainly worth pursuing. -(Hemant has tried to make the (Tp*)MoOI2, from reported procedure, for comparison with the PES of the other halides (F,Cl,Br) but it appears to be unstable and not isolated as shown when Hemant and I ran absorption on his ambiguous and still not pure sample, there being no evidence of low energy CT which should be the case, overlapping the dxy to dxz,yz and dx2-y2 LF transitions as one goes from F to I in the F,Cl,Br,I series). Also it appears to be very sensitive to presence of air (O2 /Water ) especially in solution, and this may be the reason for his difficulties. This sensitivity I have previously observed also with the Tp*Mo(NO)I2 analog e.g., used as our precursor for making dithiolene complexes via ligand exchange and required special precautions that must be employed (and as has been suggested in the literature, w/r to advantages and disadvantages of di-iodo precursor vs using the di-Cl analog in this {Tp*MoNO}2+ system), which Hemant must buckle down and employ here as well in order to isolate and stabilize this complex. The take home message from preparing and purifying the Tp*Mo(NO)I2 analog that Julien Schirlin and I both learned the hard way is that it must be preped under extremely dry-deoxygenated conditions before using, as it is already extremely difficult to purify all the way; this being evident even with a silica gel collumn dried and deoxy w/r to gel and solvents used, side products/decomposition still occurr on the collumn as a result of minute traces of water ect that reduce the amt of initial pure precursor resolved upon being eluted. Thus, pure compound can be obtained, but is subsequently and easily decomposed upon solvation. This unevitable complicated decomposition upon solvation and/or use of collumn chromatography must also be considered for the oxo-Mo-di-iodo system as well, and neccesitates the use of very dry/deoxy conditions be employed and not taken lightly. Another caveat is that there are several variations on making a (Tp*)MEI2 from M(CO)6 involving the various intermediates that can be isolated

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along this reaction route (i.e.May need to try different route, e.g. see Tp*MoNO(CO)2 directly to Tp*MoNOI2). (the reported procedure for Tp*MoO(I)2 is: in situ prep of Tp*Mo(CO)3 by refluxing Mo(CO)6 (2.63g, 10.0mmol)+KTp*(3.36g,10.0mmol) +THF(85ml) -- Tp*Mo(CO)3 / then +I2 (2.54g, 10.0mmol) at RT/24hrs/conc to 20ml -- (50ml n-heptane crashed out red/brown ppt/filtered of and washed with heptane/dried in vacuo) Tp*MoI(CO)2 / . Tp*MoI(CO)2 (.542g/.941mmol)+I2 (.239g,9.42mmol) in 30ml Tol/RT-24hr/evap to dryness -- (Tp*)MoOI2 ) (XRD from residue tol/heptane layer –dk purple/black Tp*MoO(I)2 •C7H8) IR is used to monitor reaction progress by appearance/dissappearance of CO vibrational modes between 2025-1922 cm-1. Need to check stoichiometry and IR reported for reactants as this paper has lots of discrepencies, also as can see the crystal obtained for xrd came from a solution of raw residue obtained that was considered pure with respect to monitoring the absence of v(CO) in the IR, however there may be other leftover reactants and/or sideproducts that may be present ). Note: See synthetic methods to all other precursors below. 2. a.Dithiols: The H2(S-S) dithiol ligands (protonated forms of the corresponding dithiolate S-S2- dianion), commercialy availlable are S-S = tdt, bdt, bdtCl2 (of dithiolene SC=CS type; and EDT,PDT ect. of dithiolate SC-CS type; and diols of both types H2bdo, H2EDO ect, diolates being unprotonated dianions; and thiols HSR/SPh, SPhR R=H, Me,Cl ect, thiolates being nonprotonated monoanions). Other dithiolene ligands e.g., such as qdt2- and edt2- dithiolate dianions, must be synthesized from availlable precursors (generally non S containing) that can be converted to some form from the corresponding dianion ( dithiolate salt of dithiolate dianion or protonation of dithiolate dianion to dithiol.). Note: These 1,2-dithiolenes S-S2- (dithiolate dianions) are designated as ene-1,2-dithiolates. However, the edt2- ligand is a true ene-1,2-dithiolate (able to undergo facil redox changes), while bdt2- and similar ligands which do possess a -SC=CS- chelate, are really an aromatic 1,2-dithiolate instead, due to being conjugated –delocalized with the benzene ring. However, to a 1st approximation, such aromatic dithiolates are considered in general to represent the ene-1,2-dithiolate w/r to the SC=CS portion, and has been found to be reasonable. (see valence bond approach w/r to S-C/C=C metrics). (see reported dithiolene ligands, where for the exceptions mentioned above must all be synthesized). A recognized problem with HSR thiols and H2(S-S) dithiols (dithiolene/dithiolate type) are their propensity to be decomposed in air. A particular problem is their sensitivity to air, being oxidized facily by oxygen to disulfides; the extent of this sensitivity appears to be dependent upon the nature of the dithiol; e.g. PDT decomposes by 30% within 30 min upon exposure to air while much larger chelate rings are less susceptable and may take weeks to exhibit signs of decomposition, also S rich dithiolenes (e.g. (HS)4Benz) are extremely susceptable to air oxidation, in particular in solution (and especially in the presence of a base which deprotonates the dithiol and subsequently forms the dithiolate dianion in solution, being more prone to decomposition ), as compared to a less S rich dithiol such as (HS)2Benz (=H2bdt). The increased potential for decomposition upon base addition which acts to deprotonate the dithiol in solution to a free dianion dithiolate ligand reflects the greater sensitivity of this resulting dianion in solution vs the protonated dithiol free ligand whether in solution or not. Further, the external appearance of the dithiol in solid may over a periode of time not reveal the presence or extent of oxidation even when isolated from this, thus even minute changes can upon char reveal decomposition. The presence of water w/r to this ligand at this point is not problematic here, and in fact can be used as a solvent. However, H2S-S exposure to O2 must be minimized at all times. Thus, to ensure the purity of the dithiols (commercial or synthesized), we have routinely employed a special vacuum distillation setup for this purpose, in particular for collecting the purified thiol/dithiol ligands that are liquids at RT/1 atm (HSPh/ H2(bdt)/ H2EDT) under Ar, free from water/oxygen/disulfides and other contaminants. The H2tdt and H2bdtCl2 ligands commercially availlable are solids at RT, and are generally used as received (but are dried/deoxy by gentle purging cycles under vacuum prior to use at slightly elevated temperature). This setup is similar to that previously employed by Julian Schirilin/Jon Mcmaster for the final purification of synthesized H2bdt proligand following a specific lit procedure from HSPh that reported the highest yield and purity of all methods published. This brings up another issue, especially with respect to commercial H2bdt which is obtained in 100 or 500mg sample vials (~1ml- ) rather expensive and of such small quantity making it difficult to purify this way (note: pure synthesized

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H2bdt is obtained from this method is relatively clear crystalline material when maintained in fridge, turning yellow/brown upon exposure to air or time; while commercial H2bdt is brown liquid at RT upon purchase, thus distilling of commercial H2bdt requires a large (and expensive) investment making its purification by direct synthesis more convenient than purifying commercial material. Julian and I subsequently used the synthesized H2bdt ligand in all of our synthysis employing it while the supply and integrity lasted; the ligand being stored in fridge, would over time turn brownish, and hence prior to adding to reactions we would again redistill the parent H2bdt synthesized/purified by this method to obtain ultra pure proligand prior to adding it in our reactions. This was so for the Tp*MoNO(bdt) synthesis. Eventually, this material was used up before Julian left, and required me to make additional ligand by this method. I was able to use this new material (distilling prior to use) in subsequent reactions to make more Tp*MoNObdt, Tp*MoO(bdt) and also for making Tp*WObdt, and [MoO(bdt)2]-, but unfortunately this material was unknowingly left out in the air exposed by others,and was subsequently unuseable afterwards. This required that commercial H2bdt be employed in making additional Tp*MoE(bdt) complexes and later the Cp2M(bdt) complexes, which was initially distilled from the commercial material at great effort prior to use. However, the success of purifying commercial/ and presynthesized H2bdt by this distillation setup suggested that HSPh and H2EDT, which are commercially availlable in large cheap quantities (100ml or greater) making purification by this setup affordable for these latter dithiol ligands obtained commercially, possible. This was initially applied with HSPh in the synthesis of ~10g of the [MoO(SPh)4]- precursor, which was used in subsequent reactions with purified H2bdt to make MoO(bdt)2]-. This precursor is extremely sensitive in solution to air, and difficult to handle, and decomposes rapidly unless precautions are taken. Using an anaerobic cell, the progress of the reaction is easily monitored by EA with the dissapaerance of the precursor low energy CT band () followed by the concommitant appearance of the lower energy CT band () upon substitutiion of 4SPh ligands for 2 bdt bidentate chelating ligands. EPR can also be used to monitor the reaction progress. A similar synthesis from this precursor using commercial H2bdtCl2 was employed to make the new complex [MoO(bdtCl2)2]- (note that longer reaction time is required for full conversion of this precursor ~2x as long else get a mixture including complex with partial conversion 1bdtCl2 and 2SPh ligands confirmed by MS (also HSPhCl commercial ligand to make corresponding SPh analog as previously reported). Further reactions with this precursor included making MoO(EDT)2]-, where H2EDT, obtained commercially possessed significant contaminants, and if not distilled resulted in a very difficult reaction mixture to separate (usually an oil) also a problem in the Tp*MoO(EDT) system. Thus, Pablo Bernardson was directed by me to distill this commercially purchased H2EDT ligand using this method. This was successful and the ligand was subsequently used to make the MoO(EDT)2]- complex. Note: Here is a point for digression. This was the time where I took Pablo under my wing to show him and to demonstrate how to synthesize air sensitive complexes using the appropriate schlenk methods and equipment (in this case, an extreme synthetic example requiring very rigorous exclusion; and futher consider that not many could take these lessons to heart and eventually apply successfully on their on, which is the goal all teachers/mentors hope/ (or should) for their proteges). This was necessary as his previous attempts to synthesize less sensitive complexes had been difficult under the direction of himself and others (no clear understanding of adv. synthetic techniques whatsoever at this point) and such being the case could have clearly demoralized to such an extent that future progress (as those for certain little setbacks in any research project eventually occur) could have been retarded. A similar situation (lack of confidence due to misinterpretation of limited success; which was nothing more than the absence of proper guidance and positive experience) was also apparent with a previous undergrad student and several recent graduate students. All that is needed is to take a little time, interest and initiative to motivate an individual, who we sometimes forget is there to learn and aspire to self sufficiency. As a postdoc, I firmly believe that it is our responsibility to facilitate both grad and undergrad research, even at the expense of relinquishing full credit of a project well in progress upon the inclusion of those with very little experience and in the latter exp stages. This direct participation of postdocs has a high payoff; this is I believe is the success of JHE research, and results in the well known world class quality of students fortunate enough to be involved; specifically the highest caliber of grad/undergrad students availlable and in my direct experience and good fortune these are Hemant K. Joshi(G)/Pablo Bernardson(ug)/ Julien Schirilin (ug) along with others I was less involved with. The latter part of this synthesis I introduced eventually to Pablo, although

9

simple in theory, involving a direct ligand exchange of H2(S-S) with the previously prepared and purified MoO(SPh)4]- precursor, however presented very difficult challenges w/r to maintaining total exclusion of water and air, and thus provided the perfect system for him to learn schlenk techniques and master the art of air free synthetic methods that are applicable for any system, especially regarding how to develop and experimentally setup a reaction route with total control of the environment (minimizing all potential extraneous variables in the process). This voluntary tutoring (of which I allways give freely for those who want to learn) with detailed explanation of each step has served him well, allowing him to pursue and achieve independently other projects later. Specifically, he assisted me in the 2nd synthetic batch of MoO(bdt)2]-, watching and learning, which was further remphasized by assisting me in the final syntheses of the MoO(EDT)2]- compound (the most difficult to obtain in purified form, being isolated as a salt of, but highly susceptible to decomposition even under conditions that generally were accepted as rigorous , that would occur nonetheless unless very extreme conditions and precautions were employed ) . As a resultof his desire to learn and willingness to participate, he was directed to write up his observations of this synthesis and methodology experience in a report submitted for his undergraduate research. This was an important learning experience imparted. I was fully aware that this reaction could go various ways for a number of reasons and thus even the best laid plans do not always give you the desired results, and as in this case rather than giving up or starting over, it is best to think why, and what can be done to overcome the problems even though they appear insurrmountable, i.e. adapt/ never give up so easily. I have seen other graduate students involved with this synthetic system of complexes give up. The confidence obtained with a successful preparation and continued perserverence, imploying clearly defined systematic methodologies is evident, and should provide a catalyst for further independent studies on his own merit, as indeed he has shown and proven. In fact, I wish to state that his understanding and appreciation is now such that he is approaching developed skills and techniques that never takes the short cut for expediency for any case, but rather looks for additonal ways, even if more time consuming for such small details to better control and reduce the variables involved in a synthetic reaction. This is a characteristic required for an exceptional experimental synthesist. The same can be said for Hemant, who also has this potential, but at the present time is more focused on spectroscopically studying the samples giving to him; note that I was also the same way being a hardcore spectroscopist when an undergraduate and most of my graduate studies, and finally at the end reallized this is great but unfortunately as one cant depend always on someone else to provide the things you wish to study (and with reliable purity) it becomes very obvious and necessary for one to be self suffient and reliant in order for obtaining the necessary samples for rigorous spectroscopic study with confidence and reproducibility. Hemant I believe can if pushed, excell at the highest levels as both a synthesist and spectroscopist, this being the best situation for providing clear and innovating insight into both fields, and thus the ability to carry out very independent and well rounded bioinorganic/inorganic research without being handicapped/limited. Thus the ability for a spectroscopist to achieve excellence in both fields is important; we are chemist after all, even though we may be a theoretician at heart. Q.What are the properties of these ligands (mp/bp/d/mwt ect). The properties of these ligands in solution, and/or isolated as free dithiols or salts of the dithiolate are important . -Na2bdt can be prepared directly from H2bdt (commercial or synth) in MeOH/ + NaOMe/MeOH, or from deprotection of a protected precursor synthesized, and subsequently can be isolated (sol?), then acidified by HCl to its dithiol form and extracted by (sol?) to be distilled in vac. JS has also provided me synth H2bdt. In a similar manner, HSPh, H2EDT(and related dithiolates such as PDT etc) can be converted into their Na (or K) salts. H2tdt can also be converted into its K salt. -It is known that the salts of dithiolates vs protonated dithiol forms are more stable, and thus more readily purified, and can be stored for longer periodes. b.H2qdt was preped by lit methods from its Na2qdt form. Sol diffs? Hemant has also provided me H2qdt. c.Na2edt was prepared and purified by Pablo using a multistep procedure shown below, similar to the synthetic route reported previously in the literature. Note:Any char? Can we try to submit a sample of it (and its protected precursor) prepared prior to reaction, say for H1NMR/13C-NMR and compare to reported, and ensure purity of it? Note:What happens to it in reaction solvent and subsequent exposure to air etc, so can use as control for monitoring presence or similar decomp products in reaction product. Can we remove excess or decomp products based on its behavior from reaction prod mixture? Note:Can we protonate edt dithiolate, if not why etc?

10

Preparation of Disodium Ethylene Dithiolate: as obtained using reported procedure. Taken from Pablos Syntheses and Report. Part 1. Preparation of cis-1,2-bis(benzylthio)-ethylene

Compound Amt. needed mmol FW mp (ºC) bp (ºC) density cis-1,2-dichloroethylene

10 g 104 96.94 -80 60 1.284

Toluene-α-thiol 17.7 ml 151 124.21 194-195 1.058 KOH 40.38 g 727 56.11 Ethanol 160 ml 46.07

Toluene-α-thiol + cis-1,2-dichloroethylene cis-1,2-bis(benzylthio)-ethylene Toluene-α-thiol was distilled and stored in a refrigerator prior to use.

In a 250 ml round bottom flask, KOH (40.38g, 727 mmol), ethanol (160 ml, absolute) and distilled toluene-

α-thiol (17.7 ml, 151 mmol) were stirred and refluxed under an atmosphere of dry Argon gas for 3 hours.

See Figure 1. After 1 hour, all of the KOH should have dissolve and the solution turned to a very dark

brown almost black color.

Figure Reaction Apparatus

SH

Cl

Cl

S

S+

ethanolKOH

11

FEI Note: see safety note below as this setup wrong. The Ar flow on bottom must be turned off, instead flow from top with Ar and close the bottom valve. Set flow such that backflow/press minimized.

Cis-1,2-dichloroethylene (10g, 104 mmol) was then added drop-wise to the solution at the boiling point

over 30 min. After adding only 1 ml of cis-1,2-dichloroethylene a precipitate began to form and the color

of the solution appeared light brown. The formation of cis-1,2-bis(benzylthio)-ethylene is highly

exothermic, therefore, cis-1,2-dichloroethylene must not be added too quickly.

Safety Note: The above reflux setup needs to be modified, w/r to this reaction. By the top being open, and

a pos flow of Ar introduced through the bottom flask, the point and whole ideal of doing reflux can be

thwarted; as this open sytem under pos flow (motivated by the misguided idea that this is reflux and air

free) can push/carry the volatils out the exit, with loss resulting in conc reaction mixture. However, this not

only defeats the purpose of reflux (be better to close system with septa under Ar) but is dangerous as it

results in a fire hazard/exposure from solvents; but here it is more dangerous as the reaction at temp(bp)

produces volatils that upon exposure to air ignite, which was the case for Pablo observed by the fire at the

top/exit point of his reflux condenser open to the air, as a result of pos Ar flow making this occur even with

cooled condenser (cooling –condensation of volatils is overcome by sufficient enough Ar flow.) Turning

off the bottom Ar flow stopped the fire immediately, as cooling could now prevent escape of volatils. The

point being, reflux can be done under Ar in a nonclosed system by applying a slight Ar flow to top of

condenser -as we do in flash chromatography- (where overpressurizing is eliminated by external mineral oil

bubbler system with pos Ar excess directed back through and out to open air access , that can be connected

to a trap for volatils if they escape reflux condenser)/ where the bottom reflux schlenk flask sidearms are

closed w/r to any flow in or out in this specific case. The possibility of fire was mentioned in reported

procedure but not where, why and specific precautions taken ( just that don’t expose to air for

decomposition of target and fire hazards implied w/r to target product isolated). Point is make sure cooling

flow or coolant temp (water vs isoprop) is suffient at bp of mixture such that efficient reflux occurs and

hence no volatils escape from top. Such reflux can also occur with above Ar setup described above , such

that no volatils exit the reaction flask at bottom/condenser at top. For efficient reflux, flow of Ar through

condensor from bottom flask must be capped off , and if still worry about exposure toair and need to ensure

that complete dry/deoxy conditions are maintained use the apparatus described above designed to maintain

a system semi-closed under a constant blanket of dry/pure Ar introduced at top of condenser, but as

required for refluxing, still open, which occurs when system becomes overpressurized yet remains closed

w/r to introduction and subsequent exposure to air.

The product was filtered and dissolved in boiling ethanol. Insoluble impurities were filtered off while hot.

The majority of medium-length, white crystals crash out by cooling the solution to room temperature.

Additional crops were obtained by adding cold water to the mother liquors. During this process an oil had

12

formed, which was separated from the solid product, and recrystalized by dissolving in boiling ethanol,

cooling, and adding water. This was repeated until all of the oil has disappeared.

Part 2. Deprotection upon Sodium Substitution (from Pablos report, following above published procedure) Compound Amt. needed mmol FW mp (ºC) bp (ºC) density cis-1,2-bis(benzylthio)ethylene 7.643 g 28 272.43 Na metal 5.6 g 43 124.21 194-195 1.058 ethanol 30 ml, 50 ml 46.07 toluene 50 ml

ethanolNa

+Na-S

+Na-S

cis-1,2-bis(benzylthio)-ethylene disodium ethylenedithiolate Cis-1,2-bis(benzylthio)ethylene (7.643g, 28 mmol) was placed in a 250 ml round bottom flask

over an argon atmosphere using the apparatus shown in Figure 1. Ethanol (30ml, absolute) was added and

the solution was stirred and heated at 105º (oil bath temperature) until all of the Cis-1,2-

bis(benzylthio)ethylene had dissolved . Next, Na metal (5.6g, 43 mmol) was added over a period of 20 min

at which point a fluffy, white precipitate began to form. As more Na metal was added, the solution became

very thick with precipitate, therefore 5 additional 10 ml aliquots of ethanol were added during this time to

facilitate stirring. After all the Na had been added, the temperature was raised to 130º and the solution was

let stir for 45 min. It then was cooled to room temperature and brought into the glove box. Additional

crops of disodium ethylene dithiolate were obtained by the addition of 50 ml of toluene (dry, degassed).

The remaining solid was filtered and washed several times with diethyl ether (50 ml). C6H4 (SH)2 As reported, in a 1L three-necked round bottomed flask, under a constant argon pressure, were added through a septum 75 ml of hexane with a syringe followed by the TMEDA (24.2 ml) followed by a careful dropwise addition of 200 ml of butyl lithium, at first, to avoid any overheating due to potential traces of water in hexane. The mixture being thoroughly stirred, while thiophenol (15.1 ml) was carefully added dropwise. To control any overheating the flask was cooled down by an ice/water bath. The mixture was then left and stirred during two days under continuous argon pressure. Sulfur (4.65 g), previously put under argon pressure, was then carefully added to the fairly creamy yellowish mixture. The reaction flask was even cooled down with an ice bath. The reaction mixture was then stirred for one more day. The mixture was quite thick and yellowish. Careful and dropwise addition of 3M HCl solution (100 ml) was performed. Quenching of the solution was done with water (50 ml) plus ice. The solution was extracted three times with ethyl ether. The combined ethyl ether layers were then evaporated. The resulting thick yellowish oil was then distilled at atmospheric pressure and at a temperature of 78°C. A clean white distillate was obtained and conserved in the fridge where it crystallized. 9 - 10.5 ml of pure H2bdt were obtained (55 % -62% yield; reported ~95%) 3.Preparation of precursors

S

S

13

a. MOCl3THF2 from MoCl5 (or WCl6) A modification of a reported procedure was used for isolating: MoCl5(s) /CCl4 +THF 1).(Tp*)MoOCl2 prepared as reported by adding KTp* to a solution containing MoOCl3THF2 generated in situ (or isolated) from MoCL5 and THF (reaction being highly exothermic and thus must be cooled). Purification followed procedures well established in this lab. In a 250 ml round bottomed flask, 6.50 g (23.831 mmol) of MoCl5, sitting in a dry ice bath with acetone (-70ºC), was vigorously stirred under argon while 60 ml of dry tetrahydrofuran was slowly syringed in. On addition of the first couple of drops into the flask, under constant argon pressure a thick white fume was observed. The mixture was brought slowly to room temperature, with constant stirring. Near room temperature the color changed from a brownish color to a greenish color, which is the color of the precipitate. To this mixture was added 10 g (23.81 mmol) of KL, and the mixture was heated to 45ºC and stirred for about 12 hours. By filtration the greenish precipitate was separated from the dark red supernatant. The precipitate was washed three times with 50ml of acetonitrile and dried in vacuo. The crude product was dissolved in 1L of boiling dichloromethane and filtered to remove potassium chloride and evaporated to dryness. Finally the green product was washed with 250 ml of acetonitrile. 7.98 g are recovered and confirmed by mass spec and TLC plate which showed no impurities. (a).(Tp*)MoO(OMe)2 prepared by Pablo from (Tp*)MoOCl2 by new more efficient method (Pablos) in MeOH with NaOMe. This is similar to the reported method I had employed previously specifically using Toluene and NaOMe instead. (b) (Tp*)MoSCl2 prepared from (Tp*)MoOCl2 from reported procedure: A suspension of (Tp*)MoOCl2 ) (1.5g, 3.1mmol) and B2S3 (0.9g, 7.6mmol) in dry/deoygenated DCM (80ml) was stirred under Ar for 24hr. The reaction mixture was filtered anaerobically,and the filtrate collected was evaporated to dryness in vacuo. The resulting residue was resolvated with 50ml of DCM and subsequently filtered at RT (this step is equivalent to reducing the volume in vacuo and subsequent filtration of the concentrated mixture). The addition of MeOH (200mL) to this solution was employed to ppt out the complex; and upon standing for 30 min , the brown solid was filtered off and washed with MeOH. Recrystallization from DCM/MeOH yielded orange-brown crystals. (EI-MS; parent ion m/z 497 vs 481 for oxo analog) 2). MoO(SPh)4]- from MoOCl3THF2 b.Tp*MECO2 from Tp*M(CO)3 from MCO6 1).Tp*MoNOI2 2). Tp*WOI2 c.Mo2O2Cl2/Br2 from 1).Tp*MoO2(Cl) 2). Tp*MoO2(Br) d.Cp2MCl2 (Commercial; from Cp2MH2)

14

(Tp*)MoO(bdt) (1)/(Tp*)MoO(tdt) (2) synthesis/isolation/purification/general characterization/ specific characterization The preparation and characterization of the related (Tp*)MoO(S2) compounds, compounds (Tp*)MoVO(bdt) (1),262,273 and (Tp*)MoVO(tdt) (2),295 were prepared from highly purified (Tp*)MoOCl2 following previously reported procedures, where the proligands (H2bdt and H2tdt) in the presence of base (TEA) afforded ligand exchange in a stirring dry/deoxygenated toluene solution under Ar at 70°C over a periode of 18-24hrs .18,29,30 All reactions and manipulations were carried out under an inert atmosphere of pure dry argon by using Schlenk techniques. Purification of organic solvents and reagents employed in the synthesis followed standard procedures. All solvents (OmniSolv and DriSolv; EM Science) were dried by distillation under nitrogen, and thoroughly deoxygenated prior to use via a combination of repeated freeze pump thaw cycling and argon saturation; solid reagents/reactants were dried in vacuo prior to use. Structural, spectroscopic and electrochemical samples were prepared under conditions (including all reagents/solvents) designed for the rigorous exclusion of oxygen and water in a glove bag under a positive pressure of argon to maintain and to ensure sample integrity. Upon conversion, the reaction mixture was filtered, and evap to dryness in vacuo. Collumn chromatography using tol(or benz) as eluant afforded relatively pure compounds. However, due to fact that precursor elutes somewhat in front of bdt complex and elutes right on the tail of tdt complex if present that results in trace amts of this lime green compound in the targets, and as we require very pure samples for subsequent spectroscopic and electrochemical characterization that are quiet sensitive to trace amts of the precursor, a 2nd collumn was employed in benzene where small fractions were collected and monitored for trace precursos by IR (Mo=O; 961 vs 932/926 cm-1) and subsequently combined and dried, following extracting the dry sample with toluene/filtering/conc/and layering with pentane/collecting and washing the filtered ppt/ resolvating with DCM –filtered ,dried in vacuo/stored . The following study was initiated prior to joining JHE group, but has provided the catalyst for additional studies to further address the results and postulates presented here. Also this is where the synthesis of (Tp*)MoO(qdt) was first published. Spectroscopic Evidence for a Unique Bonding Interaction in Oxo-Molybdenum Dithiolate Complexes: Implications for Electron Transfer Pathways in the Pyranopterin Dithiolate Centers of Enzymes Inscore, F. E.; McNaughton, R.; Westcott, B. L.; Helton, M. E.; Jones, R.; Dhawan, I. K.; Enemark, J. H.; Kirk, M. L. Solution and solid state electronic absorption (EA), magnetic circular dichroism (MCD) and resonance Raman (rR) spectroscopies have been used to probe in detail the excited state electronic structure of LMoO(bdt) and LMoO(tdt) (L=hydrotris(3,5-dimethyl-1-pyrazolyl)borate; bdt=1,2-benzenedithiolate; tdt = 3,4-toluenedithiolate). The observed energies, intensities, and MCD band patterns are found to be characteristic of the low-symmetry paramagnetic d1 LMoVO(S-S) dithiolate compounds, where (S-S) is a 1,2-dithiolene or 1,2-dithiolate ligand forming a five-membered chelate ring with the Mo(V) ion. Group theoretical arguments, in conjunction with available spectroscopic data show that the low energy S→Mo charge transfer transitions which dominate the spectral region below 28,000 cm-1 result from one-electron promotions originating from an isolated set of four filled dithiolate orbitals that are primarily sulfur in character. Resonance Raman intensity enhancement profiles constructed for observed vibrational modes below 1,000 cm-1 with laser excitation between ~930 – 400 nm have allowed for the definitive assignment of the ene-1,2-dithiolate Sin-plane→Mo dxy charge transfer transition at ~19,000 cm-1. This is a bonding to antibonding transition and its intensity directly probes sulfur covalency contributions to the redox active orbital (Mo dxy ). Raman spectroscopy has identified three totally symmetric vibrational modes at 362 cm-1

15

(S-Mo-S bend), 393 cm-1 (S-Mo-S stretch), and 932 cm-1 (Mo≡ O stretch), in contrast to the large number of low frequency vibrational modes observed in the resonance Raman spectra of Rhodobacter sphaeroides DMSO reductase (DR). The results acquired from the electronic structure studies on the LMoVO(S-S) complexes are interpreted in the context of the mechanism of sulfite oxidase (SO), the modulation of reduction potentials by a coordinated ene-1,2-dithiolate, the origin of the intense low energy absorption charge transfer (CT) feature in R. sphaeroides and R. capsulatus (DR), and the nature of the orbital pathway for electron transfer (ET) regeneration of pyranopterin ene-1,2-dithiolate Mo enzyme active sites. (Tp*)MoO(bdtCl2) (3); new model synthesis/isolation/purification/general characterization/ specific characterization Remote Ligand Substituent Effects on the Properties of Oxo-Mo(V) Centers with a Single Ene-1,2-Dithiolate Ligand Frank E. Inscore, Hemant K. Joshi, Anne E. McElhaney, and John H. Enemark* The synthesis of (Tp*)MoO(bdtCl2) was achieved by a ligand exchange reaction between the precursor complex (Tp*)MoOCl2 and free ligand H2bdtCl2 in the presence of a strong base (Et3N), as with other related compounds.16,18,20,21,27,28 The identity of the reaction product was confirmed by its high resolution mass spectrum, which shows an [M + H]+ peak that gives m/z = 619.0063 (calculated, 619.0059) and corresponds to the formula [12C21H25N6

11B32S235Cl2O97Mo] (97or 98Mo?). The product is soluble in

dichloromethane, dichloroethane, toluene and benzene. This compound appeared to be relatively stable in air; however, to ensure structural integrity and sample purity, the product was stored under argon prior to use. All reactions, synthetic operations and manipulations followed strict anaerobic procedures and were performed under a dry blanket of pre-purified argon gas using standard Schlenk techniques, a high-vacuum/gas double line manifold, and an inert atmospheric glove bag. Synthetic operations were also carried out in an inert atmosphere glove box filled with pure dinitrogen gas. The argon was predried by passing the high-purity-grade inert gas through a series of drying towers. Dinitrogen was obtained directly from a pressurized liquid nitrogen cryogenic transfer/storage dewar. All glassware was oven dried at 150°C and Schlenk ware was further purged by repeated evacuation and inert gas flushes prior to use. Tetrahydrofuran (THF) and toluene were distilled from Na/benzophenone; triethylamine was distilled from Na/K amalgam.25 The prepurified solvents were subsequently transferred and stored under N2 over fresh drying agents. These solvents were freshly distilled under nitrogen prior to use, thoroughly degassed by repeated freeze-thaw-pump cycles, and transferred to reaction vessels via steel cannulae techniques under a positive pressure of inert gas. Dichloromethane, 1,2-dichloroethane, cyclohexene, toluene (EM Science, Omnisolv), n-hexane and n-pentane (Burdick and Jackson) were used as received and deoxygenated by argon saturation prior to use. Solvents employed in the spectroscopic characterization studies were degassed by freeze-thaw pump cycling before use. The 1,2-dichloroethane used in the electrochemical studies was of anhydrous grade (EM Science; Drisolv) and required no further purification. Reagents were generally used as received. Molybdenum pentachloride (MoCl5, Aldrich) was dried in vacuo and stored under dinitrogen prior to use. Potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate (KTp*) and the precursor complex, (Tp*)MoVOCl2, were prepared according to literature procedures.18 The ligands H2bdt (1,2-benzenedithiol) and H2bdtCl2 (3,6-dichloro-1,2-benzenedithiol) employed in the syntheses of the (Tp*)MoVO(S-S) compounds (1, 3) were used as received from Aldrich. The preparation of (Tp*)MoO(bdt) (1) followed from published procedures.20,21 The synthesis, isolation, purification and characterization of (Tp*)MoO(bdtCl2) (3) is described below. Highly purified (Tp*)MoOCl2 (500 mg, ) was added to an evacuated Schlenk flask and dissolved in 50 ml of dry degassed toluene. The mixture was deoxygenated thoroughly with argon saturation while being stirred at ~80°C. Solid H2bdtCl2 (220 mg, 1.1 equiv) was added in slight excess to the suspension under a

16

positive pressure of argon. The resulting solution was purged with argon for 20 minutes. Dry degassed Et3N (0.40 ml, 2.2 equiv) was added slowly dropwise via gas tight syringe to this rigorously stirring solution. The mildly refluxing reaction solution was observed to change gradually from an emerald green to a dark red-brown color after 4 hours of stirring. The reaction progress, and hence optimal yield, was monitored by TLC analysis (silica gel 60 F254 plastic sheets, EM Science). The reaction was stopped upon observing the near disappearance of the green (Tp*)MoOCl2 precursor concomitant with the maximal formation of the red-brown product. Upon completion of the reaction, the blue-green precipitate, primarily Et3N⋅HCl resulting from the hydrogen abstraction and ligand exchange processes, was filtered off the hot solution under dry argon. The filtrate was cooled to room temperature and evaporated to dryness with a rotorary evaporator. The solid red-brown residue was re-dissolved in toluene, concentrated under vacuum, and layered with n-pentane. The red-brown powder precipitate was collected by filtration and washed with n-pentane until the eluant was clear. The powder was then dissolved in dichloromethane, filtered to remove any insoluble materials, and evaporated to dryness in vacuo. The solid was pumped on for several hours to ensure dryness and the complete removal of excess triethylamine (Et3N). The solid material was re-dissolved in dichloromethane, concentrated, and loaded on a silica gel chromatographic column (70-230 mesh, pore diameter 60 Å, Aldrich) under a positive pressure of argon. A red-brown fraction (band #2) eluted off the column using dichloromethane: cyclohexene (1:3) as the eluant. The purity of (Tp*)MoO(bdtCl2) was confirmed by TLC analysis. The red-brown powder was evaporated to dryness in vacuo. The compound was re-dissolved in dichloromethane, and layered with n-pentane to yield a dark red-brown crystalline material. The crystalline material was filtered, washed and then dried in vacuum. The product was characterized by IR, UV/VIS, EPR and mass spectroscopy. Suitable crystals (burgandy plate) for X-ray diffraction studies were obtained by a slow diffusion of n-pentane (or n-hexane) into a concentrated dichloromethane solution of purified 3. Mass spectra were recorded on a JEOL HX110 high-resolution sector instrument utilizing fast atom bombardment (FAB) ionization in a matrix of 3-nitrobenzyl alcohol (NBA). Infrared (IR) vibrational spectroscopic data were collected on a Nicolet Avatar ESP 360 FT-IR spectrophotometer. The IR spectra (4000-400 cm-1) were measured in KBr disks or as dichloromethane solutions (between NaCl plates) at room temperature. Electronic absorption spectra of samples solvated in 1,2-dichloroethane solutions were recorded with a 1-cm pathlength Helma quartz cell equipped with a teflon stopper, on a modified Cary 14 (with OLIS interface, 250-2600 nm) spectrophotometer. Quantitative absorption spectra were acquired at 2.0 nm resolution using a dual-beam Hitachi U-3501 UV-vis NIR spectrophotometer calibrated with known mercury lines and a 6% neodymium doped laser glass standard (Schott Glass). Absorption spectra were analyzed using Hitachi supplied Grams software. Electron paramagnetic resonance (EPR) spectra at X-band frequency (~9.1 GHz) of solution (298 K) and frozen glasses (77 K) were obtained on a Bruker ESP 300 spectrometer. The EPR samples were prepared as 1.0 or 2.0 mM solutions in dry degassed toluene. Cyclic voltammetric (CV) data were collected on a Bioanalytical Systems (BAS) CV-50W system. BAS supplied software provided scan acquisition control and data analysis/graphics capabilities. The electrochemical cell employed was based on a normal three-electrode configuration. This cell consists of a platinum disk working electrode (1.6 mm diameter, BAS), a platinum wire counter electrode (BAS) and a NaCl saturated Ag/AgCl reference electrode (BAS). Prior to each experiment, the electrode was polished using 0.05 µm alumina (Buehler) and electrochemically cleaned in dilute sulfuric acid. Cyclic voltammetric measurements of (Tp*)MoO(bdtCl2) and related (Tp*)MoO(S-S) complexes were performed in dry degassed 1,2-dichloroethane solutions (10 ml, ~1mM, 25°C) over a potential window of ± 1.5 V vs. Ag/AgCl with 0.1 – 0.2 M dried tetra-n-butylammonium tetrafluoroborate [n-Bu4N][BF4] (Aldrich) as the supporting electrolyte. The background scans of dry/deoxygenated DCE with the [n-Bu4N][BF4] supporting electrolyte exhibited no electroactive impurities or solvent decomposition within the potential window employed. Ferrocene was utilized as an internal standard, and all potentials were referenced relative to the Fc/Fc+ couple. He I gas-phase photoelectron spectra (PES) were collected on a spectrometer with a 36-cm radius hemispherical analyzer (8 cm gap, McPherson), sample cells, excitation sources, and detection and control electronics using methods that have been previously described in detail.22 The absolute ionization energy scale for the He I experiments was calibrated by using the 2E1/2 ionization of methyl iodide (9.538 eV), with the argon 2P3/2 ionization (15.759 eV) used as an internal calibration lock during the experiment. During data collection the instrument resolution (measured using the FWHM of the argon 2P3/2 ionization peak) was 0.020 – 0.023 eV. All data were intensity corrected with an experimentally determined instrument analyzer sensitivity function. The He I spectra were corrected for the presence of

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ionizations from other lines (He Iβ line, 1.9 eV higher in energy and 3% the intensity of the He Iα line). All samples sublimed cleanly with no detectable evidence of decomposition products in the gas phase or as a solid residue. The sublimation temperatures were monitored using a “K” type thermocouple passed through a vacuum feed and attached directly to the aluminum ionization sample cell. The sublimation temperatures (in °C, 10-4 Torr) were as follows: (Tp*)MoO(bdtCl2), 198°; and (Tp*)MoO(bdt), 183°. (Tp*)MoO(qdt) (4);synthesis/isolation/purification/general characterization/ specific characterization A new purification procedure allowed this previously reported complex to be isolated with ultra purity and suitable crystals obtained for XRD char. Previously, considerable effort to do this over 2 years had failed for original authors. Not untill a procedure was developed producing ultra pure sample was this finally possible. The same solvent choice det here for XRD crystals applied to sample prepared by previous methods did not result in crystal formation. Molecular Structure and Vibrational Studies of an Oxomolybdenum Complex with a Charge Deficient Dithiolate [Hydrotris(3,5-Dimethyl-1-Pyrazolyl)-Borato](Quinoxaline-2,3-Dithiolato)-Oxomolybdenum(V): Remote Ligand Effects on Geometric and Electronic Structure of Oxo-Mo Ene-1,2-Dithiolates. Frank . E. Inscore†, Nick. D. Rubie‡, Hemant. K. Joshi†, Martin. L. Kirk‡* and John. H. Enemark†* General. Unless otherwise stated, all reactions and manipulations were carried out under an inert atmosphere of pure dry argon by using Schlenk techniques. Structural, spectroscopic and electrochemical samples were prepared under conditions (including all reagents/solvents) designed for the rigorous exclusion of oxygen and water in a glove bag under a positive pressure of argon to maintain and to ensure sample integrity. Purification of organic solvents followed standard procedures. All solvents (OmniSolv and DriSolv; EM Science) were dried by distillation under nitrogen, and thoroughly deoxygenated prior to use via a combination of repeated freeze pump thaw cycling and argon saturation. The preparation and characterization of the quinoxaline-2,3-dithiol (H2qdt) ligand followed previous reported methods.41-4428 (Tp*)MoVO(qdt) (4) was prepared by published methods.16,17 The compound (Tp)*MoO(qdt) dissolved in a minimum amount of toluene was chromatographed on silica gel (70-230 mesh) and eluted in a binary mixture of toluene: 1,2-dichloroethane (1:1) as a red band. The red fraction was collected and evaporated to dryness in vacuo. The solid residue was resolvated in a minimal amount of dichloromethane, and the addition of hexane, layered on the concentrated solution (1:1), induced a deep red-brown powder to form, which was subsequently washed and dried upon collection. The (Tp*)MoVO(qdt) (4)18,19,36 and related (Tp*)MoO(S2) compounds compounds (Tp*)MoVO(bdt) (1),262,273 (Tp*)MoVO(tdt) (2),295 (Tp*)MoVO(bdtCl2) (3),306 and (Tp*)MoVO(SPhMe)2 (5) 295 were prepared from (Tp*)MoOCl2 following previously reported procedures.18,29,30 (Tp)*MoO(qdt) was further purified under argon by a combination of multiple extraction (toluene/pentane; dichloromethane/hexane) and flash chromatographic steps (silica gel 230-400 mesh, Aldrich; eluted in binary mixtures of toluene: 1,2-dichloroethane (1:1) and dichloromethane: cyclohexane (1:2) as a red band). The final red fraction was collected and evaporated to dryness in vacuo. The solid residue was resolvated in a minimal amount of dichloromethane, and the addition of hexane, layered on the concentrated solution (1:1), induced a deep red-brown powder to form, which was subsequently washed and dried upon collection. Highly purified samples of 4 submitted for physical characterization were obtained by a slow diffusion of n-pentane into a saturated dichloromethane solution. The (Tp*)MoO(qdt) complex and other compounds investigated were identified by their characteristic UV/VIS and IR spectroscopic features.16,22,25-27 Reaction progress and purity of isolated compounds were monitored by thin-layer chromatography (silica gel 60 F254 plastic sheets; EM Science) and mass spectrometry. High resolution mass spectrometry showed (Tp*)MoO(qdt) (4) to have an [M+H]+ experimental mass of 604.0889 with respect to the most abundant 98Mo isotope (calculated: 604.0902). The reduction potential (relative to the Fc/Fc

+ couple in 1,2-dichloroethane) of (Tp*)MoO(qdt) (-461 mV) is consistent with that previously reported19,36 for 4 and follows trends in the quasi-reversible Mo(V)/Mo(IV) couples observed for 4-1 in 1,2-dichloroethane.30,33 The (Tp*)MoO(qdt) complex and other compounds investigated in this study were further identified by their characteristic IR, EPR and UV/VIS spectroscopic

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features.18,19,26,27,29,30,36 The identity of the (Tp*)MoO(qdt) complex (4) was confirmed by an X-ray crystal structure analysis. Suitable crystals of the The (Tp*)MoO(qdt) (4) complex (4)were obtained as listed in Table 1 was structurally characterized by X-ray crystallography. Suitable crystals (dark-red blocks ) were obtained by slow vapor diffusion of pentane into a dichloromethane solution at room temperature. Physical Measurements. 1H- NMR spectra of the H2qdt ligand (in DMSO-d6) were obtained with a Bruker AM 500 spectrometer. Mass spectra were recorded on a JEOL HX110 high-resolution sector instrument utilizing fast atom bombardment (FAB) in 3-nitrobenzyl alcohol solutions. Cyclic voltammetric (CV) data were collected on a Bioanalytical Systems (BAS) CV-50W system with an electrochemical cell consisting of a platinum disk working electrode (1.6 mm diameter, BAS), a platinum wire counter electrode (BAS) and a NaCl saturated Ag/AgCl reference electrode (BAS). Cyclic voltammetric measurements were performed in 1,2-dichloroethane solutions (10 ml, ~1mM, 25°C) with 0.1 – 0.2 M dried tetra-n-butylammonium tetrafluoroborate [n-Bu4N][BF4] (Aldrich) as the supporting electrolyte. Ferrocene was utilized as an internal standard, and all potentials were referenced relative to the Fc/Fc+ couple. IR spectra were measured on solid (KBr disks) and solution (dichloromethane between NaCl plates) samples on a Nicolet Avatar ESP 360 FT-IR spectrophotometer. .Electron paramagnetic resonance (EPR) spectra at X-band frequency (~9.1 GHz) of solution (298 K) and frozen toluene glasses (77 K) were obtained on a Bruker ESP 300 spectrometer. Electronic absorption spectra of samples solvated in 1,2-dichloroethane solutions were recorded on a Cary 300 (250-900 nm) or a modified Cary 14 (with OLIS interface, 250-2600 nm) spectrophotometer. Details of the electrochemical and spectroscopic he IR and UV-visible measurements for these complexes have been described previously.186,19,262,295,30-,3627 (Tp*)MoO(edt) (5) new model synthesis/isolation/purification/general characterization/ specific characterization/DFT calc Paper in Progress: Note: This is the final complex synthesized in my research here. The success of this syntheses lies in the extreme dry/anaerobic setup and rigorous conditions employed in all aspects of the reaction, and I do mean extreme for every step as I will discuss and why(complete control) . I have included Pablo and Hemant as collaborators. Pablo provided the Na2edt ligand from a previously reported procedure. This ligand required deprotection and purification prior to addition to reaction flask, this ligand was pablos primary contribution to the 1st synthesis/purification/characterization, but still a very important component and this clearly warrants his name on this paper, and as he has been coupled into what is going on in this synthesis and has and will continue to provide assistance w/r to this preparation, for him also to write the synthesis of Tp*MoOedt up in his thesis. Unfortunately, he had to depart to Japan that afternoon (the next day) and so was not present in the isolation/purification/char steps that followed for the next several weeks. Also I have had him working on a new precursor to try and make the the target of this study by a different route. I have also coupled Hemant as usual for some characterization. Specifically, after isolation,purification and recrystallization steps I generally supply suitable crystals for XRD to facility and hemant does the structure refinement. In this particular case I have had hemant under my direct supervision prepare samples anaerobically, for possible crystals using a variety of solvents (recently purchased by me for this purpose), chosen based on my previous solubility profiles. This XRD if obtainable, puts Hemant on the paper. After obtaining pure samples, they are characterized by MS,IR,EPR,EA,CV, and then afterwards some are submitted to PES facility(usally to Hemant). This and some additional characterization that I cannot finish or that needing repeated will now in this case be some of Hemants responsibility, and will subsequently include this characterization in his dissertation. However, it is one thing to be giving pure sample, preped and ready for characterization. In this case, sample prep requires careful exclusion of air and water untill we obtain purityand know the stability, and all of this will now have to be done by Hemant, and there are

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no shortcuts. Furthermore, additional compound will be needed, and if they follow my methodology and suggestions it should be no problem. The Synthesis and Characterization of (Tp*)MoO(cis-ethene-1,2-dithiolate): A New Minimal Structural Model and Effective Spectroscopic Benchmark for Probing Contributions to Geometric Distortions Observed in Folding of the Dithiolate Chelate Ring and Effect on Electronic Structure The synthesis of (Tp*)MoO(edt) was achieved under an inert atm of Ar by a ligand exchange (substitution) reaction between the highly purified precursor complex (Tp*)MoOCl2 and sodium salt of the dithiolate ligand Na2edt employing rigorously dry oxygen free conditions in a nonpolar solvent(Tol) at elevated temp. This is in contrast to the synthetic route reported for other related (Tp*)MoO(dithiolene) compounds availlable in this isostructural series, which employed similar reaction conditions, but utilized instead the dithiol proligand (H2(S-S), S-S = tdt,bdt bdtCl2,qdt) in the presence of a strong base(TEA). This is the 1st dithiolene in this series prepared/reported in such a manner, showing that this is a viable route to other (Tp*)MoO(dithiolene) complexes. However, the (Tp*)MoO(EDT) complex possessing a saturated 5-membered chelate ring (SC-CS) coord to Mo (as was several other related dithiolate complexes)r was previously prepared from both the Na and K salt of the dithiolate ligand.r The identity of the reaction product was confirmed by its high resolution mass spectrum, which shows an [M + H]+ peak that gives m/z = (calculated, ) and corresponds to the formula [12C17H25N611B32S2O98Mo]. The product is soluble in dichloromethane, 1,2-dichlorethane, toluene and benzene. This compound appeared to be relatively stable in air for a short time, however, to ensure structural integrity and sample purity, the product (dried and purged in vacuo) was stored in a schlenk flask under Ar and transferred to an inert atm glove box untill needed. Subsequent manipulations and sample preparations were performed under a dry Ar atm with solvents employed being relatively dry and thoroughly deoxygenated. Preparation of Compounds General: Materials and Methods Preparation of Ligands 1. KTp* was prepared and purified by following well established procedures as reported and further developed in this lab. 2. Na2edt was prepared and purified by a multistep procedure, similar to a synthetic route reported previously in the literature. Note:Any char? Can we try to submit a sample of it (and its protected precursor) prepared prior to reaction, say for H1NMR/13C-NMR and compare to reported, and ensure purity of it? Note:What happens to it in reaction solvent and subsequent exposure to air etc, so can use as control for monitoring presence or similar decomp products in reaction product. Can we remove excess or decomp products based on its behavior from reaction prod mixture? Note:Can we protonate edt dithiolate, if not why etc? 3. other ligands that may be used? H2(S-S), Na2(S-S); where S-S = bdt (others tdt,bdtcl2,qdt,mnt; EDT) Preparation of precursors 1.(Tp*)MoOCl2 prepared as reported by adding KTp* to a solution containing MoOCl3THF2 generated in situ from MoCL5 and THF. Purification followed procedures well established in this lab. 2.(Tp*)MoO(OMe)2 prepared from halide precursor by new methods in MeOH with NaOMe, but similar to that reported using Toluene and NaOMe. Note: make sure char(MS/IR/EA/CV/EPR) and TLC to ensure purity of both precursors prior to reaction, and to provide controls for determining reaction progress and their presence in isolated products. Any side products of these should we be aware of? Based on properties and behavior can we remove excess or side products from reaction mixture containing target dithiolene complexes?

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Note: Consider properties of all the reactants/reagents and expected products (target/other prod/excess reactants/side prods etc for how to remove. Preparation of Model Complexes See reaction route scheme for making (Tp*)MoO(S-S) complexes, as 4 potential precursors, 4 general routes; and each can generally be subdivided into 2 sub routes depending if using dithiol (a) or salt of dithiolate ligand (b). We only consider 2 of these 4 general routes here. Primary focus is on edt complex (Method 1 from halide precursor), however bdt system is also to be looked at for new route employed here for 1st time using (Tp*)MoO(OMe)2 precursor (Method 2), and also to provide a reactivity comparison with the edt complex and especially if can employ identical reaction conditions. Note:The syntheses and char. of the secondary dithiolene complexes (bdtcl2,tdt,qdt) and dithiolate complex (EDT) to be compared to are all ready reported. All of these complexes I have synthesized for additional comparison if needed in addition to what has been already published. The chemical, geometric,electronic properties and electrochemical behavior of the target are to be compared primarily w/r to those in the bdt system (a much simpler and less bulky dithiolene system that is a true ene-1,2-dithiolate vs. aromatic dithiolate with conjugated ring) and EDT system (a 5-membered chelate ring with SC=CS vs relatively isostructural SC-CS ring system as function of saturation effects/ less restricted rotation of S orbitals in EDT). Big Q is how much does these properties change, and what effects on the fold angle does the less sterically hindered edt ligand have vs the bdt system?// how does the electronic structure change for edt vs EDT? 1.Preparation of (Tp*)MoO(edt) Method1. Method 1a. was not tried due to the difficulties in protonation of edt dianion and its subsequent instability. Method1b.The highly air sensitive Disodium ethylene dithiolate (0.29g, 2.13 mmol) ligand was prepared and purified as previously described from its protected precursor immediately prior to the reaction and subsequently dried under vacuum to avoid decomposition products. The observed sensitivity of this ligand to air is evident following deprotection and isolation, where exposure to air results in decomposition of the white powder, initially turning yellow-brown and then into a dark brown viscous semi-liquid within a matter of minutes. The purified, dry ligand was weighed, suspended in 12 ml tol and transfered slowly in a glove bag(pos press of dry Ar -flowed through drierite packed entry tube) to a green suspension (pre-purged) of highly purified dry (invacuo)Tp*MoOCl2 (0.90g, 1.87 mmol) in 25 ml of dry(distilled under Ar over Na/benzophenone/collected and transferred anaerobically from still to prepurged/evac receiving schlenk flask connected directly to vac/inert gas manifold), deoxygenated(via Ar sat/FTP) toluene and subsequently transferred to reaction flask anaerobically via steel cannula under Ar pres,s in bag, flask of stirring mixture subsequently purged by Ar sat and vacuum, heated slowly to 50º C,under Ar blanket in oil bath(mineral) at which time the color of the solution changed slightly from green to brown. The reaction mixture was let stir for another 18 hours at 70 C under an inert atmosphere of dry Argon gas Reaction mixture filtered anaerobically(hot), cooled to rt and conc to red solution, the filtrate char by MS FAB and ESI/MeCN both showed the presence of target in react.mixture(see analysis; also see presence of trace precursor). Evap to dryness invacuo/ resolv/extracted with tol under Ar, conc (tlc profile in tol) and ran down silica gel collumn anaerobically tol/tol eluant. (next time more anaerobic) note still have brown mat in flask, caked on sides etc pretty good, see some loose green evidence at bottom (residue from extraction, indicating other stuff not as sol in tol. 3 bands pulled off for identity(still dk brn bands behind and on top 1st green in schlenk flask, 2nd brown-red schlenk, 3rd left on bottom was purple; 1,2 submitted for esi ms; green showed to be target, slight halide precursor trace evident, neither in band 2 from ms. Tlc of left over green ms sample after submitted and identified as targ (or the subsequent dried green fract)., only 1 spot in tol ,consistent with previous behavior of TLC profile prior to collumn separation as anticipated. Tlc control of cl2 prec vs green in tol or tol/dcm show they both elute the same , cl2 slightly tailing, thus this and fact very minute amts of cl2 implies difficulties in sep excess cl2 from target.How to ensure very pure? Green fract conc/ and dried in vac anaerobically to remove tol Resolv in dcm ,and transfer to smallerflask (vial) for storage, dry evap under Ar stream(septum sealed vial with pos press and needle in septa,, seal vial, store in glove box.

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Halide less sol in tol than edt, not sol in pentane, edt in tol/pent 1st 2 layers then becomes mixed over time; can we recrystal? Suggest: make sure cl2 is consumed completely, what is best temp and time for this, run ms sample to det if need to continue.(tlc not useful) Inc yield by ensuring all ops done anaerobically including collumn (evac gel for ox etc) Anaerobic Filtration of Reaction Mixture

External Anaerobic Solvent Remover (slows breakdown of Apeizon-N grease on schlenk manifold) Designed and installed on my schlenk line by Pablo.

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Taken out of glove box and transferred to glove bag under Ar, for preparing samples for growing crystals and initial EA. Sat sample with DCM/ transfer small aliquots of sat dcm sample to 4 vials. Recrystall: Vap diff of new pentane into 1dcm sample in sealed jar; liq diff of pentane,heptane, and hexane layered separately onto 3 DCM samples sealed. (kept in bag with pos press/ note by accident ar turned off over night. Q. is samples still ok? Also 1 dilute dcm sample preped in anaerobic quartz cell matched with cell with DCM only. Abs ran, and sample put back in bag. Q is it still ok over course of exp and after night with ar off over time? After making samples original dried again by septum and needle, also left out overnight, is it still ok? All put in glove bag this next day under Ar. Is it still on? This was not good, loss of controls-introduced new variables; poor technique and planning, now need to det if sensitive to air!!!!! However, the glove bag was not maintained as promised, thus potential for decomposition and loss of valuable product may have occurred. Q. also,did the original sample from tol change with dcm/method before storage , did dried sample change in box during storage? Need to TLC and MS to ensure. Q. also, redo ms Note: from EA, definite that the green fract is not just halide, as band at 16750 says it has something else. Could run 2nd band ea to see how it looks( does it look more like bdt complex than does green, then maybe something got messed up. Q. thus from above, the stability of target in solution and solid should be addressed. Does ab sample change over time and/or with exposure to air? With change in solvent dcm vs tol ; any possible way to knock of edt and replace with solvent or cl? Note: always control the exp, no extra variables introduced. Thus char each step, and maintain some orig materials as a control to test each step and diff conditions. Exps to do:

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1.The synthesis with halide precursor should be repeated, as this appears to be viable route to target based on fact that MS of crude product (and isolated fraction)says we made it for initial reaction(are we for sure about MS identification? Need detailed analysis) Based on presence of halide precursor in crude filtered product by MS(FAB and ESI) and subsequent isolated component assumed to be target (green fraction, band 1) based on MS(ESI) of band 1 and band 2, appears incomplete conversion of precursor is suggesting need to react for longer time (monitor dissappearance of halide by MS and IR) or higher temp to force consumption, or presence may be due to not enough ligand (or base) for some reason (dec by side react or not enough added to start with relative to halide, or too much halide added to start with thus can make sure weight of precursor known and use slight excess of ligand and base w/r to this halide combined with longer react time /higher temp and monitoring of progress to ensure complete conversion before proceeding/terminating reaction. The results/ char etc of initial reaction will be important for optimizing the 2nd reaction. Remember, retain control and don’t introduce new variables. 1. check MS (ESI in MeCN) of Green fract a. the redried septum sealed sample (solvent blown off by Ar via 2 needles in septa for several hours and these subsequently removed, thus sample at least from this point on should be ok here even though not stored in box after taking off Ar line) in vial after solvating (in bag Ar pos press) with new drisolv dcm for 2nd time for the EA and recrystall exps prepped in bag; as this is best we have left of original isolated component. -see if still observe target and halide/ compare to original this also sees if sensitive to DCM etc vs tol/ also is the green component the correct one for target identified by MS or was there a mixup between band 1 green and 2 brown? If appears mixup, still have brown component which can be tested, also have original crude tol prod in flask available that can be extracted and ran down small tol collumn. To get new green/brown fracts. If this green fract ok, then we can further test stability by opening to air for time, if not then have to backtrack. Objective 1. Evaluate the reaction route and synthetic methods for preparing (Tp*)MoOV(edt)and viabil alternatives. Showing that the reaction route produced the desired target compound , identifying the target in the isolated components during purification, and determining the purity of the target is the initial experimental objective of this study. The next objective is can we and by what means obtain pure compound for further characterization and studies? Then we can direct our focus to the primary issues and goals of specific interest regarding the study of this complex(which is ? and by what means?). Thus; I.Q. How do we know that this reaction was successful? II.Q.Considering the initial separation/isolation/purification process following the reaction, how do we monitor this and identify the target in a specific component? III.Q. How do we determine/monitor the purity/purification of the isolated target component upon being identified? NOTE: -MS combined with TLC are our primary/initial tools for monitoring the reaction progress, the nature and number of components in the reaction mixture –reactant/product, and in particular for MS, identifying the presence or not of the target compound in the crude/final product. TLC profiling is useful for determining initial conditions and methodologies to employ in isolation/purification steps,and for tracking results and

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monitoring progress/behavior w/r to product formation//purification//purity and stability of product isolated/identified. -Additional spectroscopic techniques that can be employed similarly for monitoring reaction progress/purification/ product purity,identity, and behavior include IR and NMR spectroscopy. EA, EPR spectroscopy and CV can also provide some insight into the nature and purity of isolated product. Once highly purified product isolated can be submitted for elemental analysis for insight into molecular formulation, and if obtain suitable crystals for XRD can get solid state geometric structure of molecule. -The combined results of these techniques ensure that we know the purity/stability of product isolated, its identity, electronic nature, and ultimately geometry/structure. The compound can now be used in further characterization and specific studies. MS analysis General: The identity of the target complex in the crude product reaction mixture was confirmed by MS; FAB and ESI, which show the parent ion peak associated with a peak cluster characteristic of isotopic distribution pattern of Mo, and corresponding to the mwt, in addition to identifying char peak fragments associated with the observed Mwt. The analysis of observed peak patterns is consistent with that observed for other related well characterized complexes. The identity of the isolated target during the initial separation/isolation/purification was determined and monitored by MS(ESI) following these general standard procedures. Specifically, upon filtration/ removing solvents/-volatils by evaporation to dryness in vacuo /extraction and further drying// determining solubilty properties combined with subsequent TLC analysis for monitoring /determining the isolation/purification conditions for separating out the components by extraction/recrystallization and intial collumn chromatography resulted in these isolated fractions being probed by MS, which determined the 1st band (green) isolated from collumn chromatography containing the target. The MS results of the crude product show that the reaction was not complete and that of the initial isolated target component is not entirely pure as traces of the halide precursor is present. Modifications to the reaction procedure to ensure complete conversion and higher yield is suggested (e.g. longer reaction time/ higher temp/solvent choice), or further purification becomes necessary as will be the case here for this initial synthesis. A.Q. Consider anticipated ideal structure/formulation and e- configuration of target complex: Can we identify the target with absolute certainty? If not, can we do so at least to some degree of certainty? To what extent and at what point? Analysis of certain peak fragmentation patterns and expected isotope distribution patterns could be associated with Tp*MoO ion, etc that corresponded to diffs with respect to the [M+] and its Mwt for the target complex, and the presence of a Mo containing compound. q. Is the analysis of observed peak patterns/isotopic distributions consistent with that observed for other related well characterized complexes of this system? Are we certain about this and the identity of target? B.Q. Consider reaction; reactants and products,: 1. Can we determine the extent/progress of this route? Can we identify specific reactants/ products/ side reaction and decomposition products?Any stability issues? Similar analysis of mass spectrum and comparison to previous MS data of anticipated/potential characterized complexes, as above reveals in addition the presence of: - precursor (Tp*)MoOCl2. (what is specific evidence, How much is present relative to target?) q. What does this suggest? Reaction incomplete, the complete conversion of precursor to target requires its consumption during ligand exchange with dithiolate ligand. Assuming ideal conditions and stoichiometric conversion, the presence of

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excess precursor in reaction mixture upon terminatiing the reaction indicates reaction time should be extended (and maybe at higher temperature). However, as this is limiting reagent, a loss of other reactants due to other potential side reactions (etc) may require a slight excess of these be employed to ensure complete convesion (the excess of these in mixture would not present a significant problem in removing versus the more difficult task of removing this halide precursor here. This is due to the difficulties in separating out the precursor from target w/r to same TLC behavior, thus collumn chromatography was not able to resolve (at least with solvents explored here) as they elute almost same(halide slightly elutes behind target inTol or Tol/dcm as indicated by TLC with halide control,which results in collumn isolated component having target and halide, as observed in MS. Thus may consider using other precursor such as methoxy which is prepared from and isolated from halide as reported and is also shown by TLC and collumn behavior with silica gel , eluting far behind in appropriate solvent , and hence should be well resolved from target efficiently using collumn separation methods ( providing motivation for trying, but whether this potential route is viable remains to be shown, but it appears this would work regardless of excess OMe precursor remaining). 2. How does this help w/r to further analysis, and identifying, isolating, purifying, and characterizing the target? How and what can we monitor and by what means? Need to either find a way on collumn which not promising,, or consider solubilty properties of each, and use diffs to extract or recrystalize from each other with appropriate solvents/conditions. Or redo reaction and make sure goes to completion by monitoring consumption of halideprecursor via TLC and MS during the reaction, and in addition to inc reaction time may also modify by inc temp or choice of solvent. Optional would be to use a diff precursor such as OMe for easier separation using collumn chrom techniques. In any case, MS provides the primary and most efficient means w/r to direct identification of the reaction mixture species or purity of the isolated components (e.g. isolated bands resolved during collumn chromatography). Additional means which are readily available, uncomplicated and very sensitive to monitor halide presence is IR( intense VM=O at 961, target anticipated to occur around ~943-926 in range reported for the other availlable dithiolenes in this system ), which is sensitive to trace amts. EPR is sensitive w/r to S vs halide donors and precursor trace should be manifested in spectra, similarly CV redox potentials being well sep for the halide and dithiolene complexes is an additional probe of purity. Hence, one needs to have the pure precursor well char by these techniques, as a control, in order to compare and evaluate its presence in the component containing the target. Additional insight w/r to its solubility/ other physical properties and TLC behavior is valuable for optimizing potential purification routes. Unfortunately in this case tracking by TLC does not appear to differentiate between these two component in the presence of each other. It is however invaluable for determining the purity and conditions for resolving the target w/r to other species. Observed sol properties: The product is soluble in toluene (and hence benzene) from initial reaction conditions-collumn sep and and DCM(and hence DCE) from final solvation/transfer of isolated green dried fract. Also from recry/abs green sol in dcm. Is green etc sol in MeCN since used in esi ms. From attempts to extract tol sample not initially sol in pentane layered, but does eventually mix. From recryst of dcm samples, pent, hept, hexane layered and next day was still sep green and clear somewhat. This compound appeared to be relatively stable in air for a short time, however, to ensure structural integrity and sample purity, the product (dried and purged in vacuo) was stored in a schlenk flask under Ar and transferred to an inert atm glove box untill needed. Subsequent manipulations and sample preparations were performed under a dry Ar atm with solvents employed being relatively dry and thoroughly deoxygenated.

26

(Tp*)MoSCl2 prepared from (Tp*)MoOCl2 from reported procedure: A suspension of (Tp*)MoOCl2 ) (1.5g, 3.1mmol) and B2S3 (0.9g, 7.6mmol) in dry/deoygenated DCM (80ml) was stirred under Ar for 24hr. The reaction mixture was filtered anaerobically,and the filtrate collected was evaporated to dryness in vacuo. The resulting residue was resolvated with 50ml of DCM and subsequently filtered at RT (this step is equivalent to reducing the volume in vacuo and subsequent filtration of the concentrated mixture). The addition of MeOH (200mL) to this solution was employed to ppt out the complex; and upon standing for 30 min , the brown solid was filtered off and washed with MeOH. Recrystallization from DCM/MeOH yielded orange-brown crystals. (EI-MS; parent ion m/z 497 vs 481 for oxo analog) The (Tp*)MoS(bdt) and (Tp*)MoS(tdt) compounds were prepared from this precursor following unpublished procedures by Young and coworkers (Jason P. Hill, private communication), with slight modifications, employing similar methodologies as developed for ligand exchange reactions in their oxo-Mo analogs. However, these sulfido complexes were extremely sensitive to air, and required more rigorous exclusion of oxygen/water. This extreme sensitivity, especially in solution, made characterization (CV Anne) very difficult and subsequently was not further pursued due to their propensity to decompose even under the best of conditions. (This was also observed by FEI and BW in dissertations). I was given the partial structure of bdt complex by J Hill of Dr. Youngs group, and EPR data. The following is taken from previous unpublished work under Dr. Kirk in collaboration with Dr. Young that would have included the synthesis of these sulfido-Mo complexes above. The spectroscopic protocols developed above from studies of the oxo-Mo analogs (EA, MCD, rR) have been extended to LMoVS(bdt) and LMoVS(tdt) terminal sulfido complexes. These studies were directed towards deriving insight into the relative electrophilicity of terminal oxo and sulfido ligands in LMoE(S-S), where E = O,S. This has extremely important implications with respect to the mechanism of xanthine oxidase. The spectroscopic studies have shown that although the electrostatic contribution to Mo≡E bonding is greater for the oxo donor (greater dxy-dxz,yz splitting), the Mo≡S interaction is more covalent, and

27

the sulfido ligand donates more charge to the metal. This effect results in the terminal sulfido being more electrophilic. In conjunction with the lower energy of the Mo≡S π* acceptor orbital, this should result in preferential attack on the terminal sulfido by nucleophiles such as PPh3 when both sulfido and oxo donors are directly coordinated to Mo. Hence, in the oxidized [MoOS]2+ site of xanthine oxidase, a reaction mechanism favoring C-H bond cleavage and hydride (H-) attack on the terminal sulfido is preferred over protonation of this sulfur ligand in the hydroxylation of xanthine to uric acid. The combined results of the LMoE(bdt) studies clearly illuminate the effects of the axial ligand on the Mo ligand field, which defines the energy of the metal based acceptor orbitals in LMCT transitions. These spectra clearly show that changes in the axial ligand field produce marked changes in the MCD spectra, supporting the interpretation of a terminal oxo cis to the pyranopterin dithiolate in the “very rapid” intermediate of xanthine oxidase. The MCD spectra of the “very rapid” XO intermediate exhibited a nearly perfect 1:1 spectral correspondence with those features in LMoO(bdt) below 28,000cm-1. This work and the above parallel studies of the oxo-Mo analog are related to the following study published. Freeze-Quench Magnetic Circular Dichroism Spectroscopic Study of the "Very Rapid" Intermediate in Xanthine Oxidase Jones, R. M.; Inscore, F. E.; Hille, R.; Kirk, M. L. (Tp*)WVO(bdt) was studied by XRD, crystals from (slow vapor diffusion of THF into ) in glove box and char further by HeI PES,epr (Tol) and DFT calcs using structure derived; and (Tp*)WVO(tdt) was char by CV(DCE),epr(Tol) and PES HeI/II in Enemark group; in addition to properties previously char and reported in FEI dissertation/ACS abstracts (FEI; Kirk/Young ); that was also presented at GRC(XRD-PES and some previous data -FEI with previous permission to make these and study further by C.Young, and permission to present previous related work by Kirk/Young)//MIBC England (CV-ET rates Anne) by Enemark group. Note: it took several solvent mixes over a periode of several months to finally get crystals in glove box. Hemant refined the XRD and took the PES HeI of bdt. Also I will do the calcs under Hemants direction. We need to get more of these complexes for closeup of S/M region to help resolve the bands. No tiime for me so suggest see if Dr. Young can supply more, and even if not we should include him in this paper and maybe include his syntheses of these complexes. Confer with MLK. The LWO(bdt) and LWO(tdt) complexes employed in this structural/spectroscopic study were prepared from the precursor complex(Tp*)WVOI2 16, 28 following unpublished synthetic, isolation, and purification procedures developed by Young and co-workers.16, 28 With the permission of Dr.Young these compounds were synthesized for the purpose of aquiring structural insight by XRD,and characterizing these complexes further w/r to their electronic structure via gas-phase PES ,CV(in DCE obtained under identical conditions as employed for oxo-Mo series of dithiolenes (and sulfido-Mo and NO-Mo analogs as well) in order to create a consistent data base for comparison and evaluating trends in redox behavior; as opposed to that measured initially in MeCN for the 2 WO dithiolenes) and DFT calcs and directly compare to the monooxo-Mo-monoene-1,2-dithiolate analogs under identical conditions aquired by us to further probe metal substitution effects (4d1 vs 5d1) in a controlled geo-coordination environment with ligand parity ((Tp*)O=M(S-S)). These previous spectroscopy studies has been published in my dissertation 2000,presented at the 1999 ACS Anaheim meeting by myself for MLK. The initial studies obtained in JHE group w/r to structure and PES was presented at the GRC 2001 by myself: Abstract GRC 2001 Ventura Electronic Structure Contributions to Reduction Potentials and Oxygen Atom Transfer Reactivity in Oxo-Mo and Oxo-W Dithiolates: Insight into Tungsten and Molybdenum Pyranopterin Enzymatic Reactivity Differences. F. E. Inscore*^, J. P. Hill^^, C. G. Young^^, J. H. Enemark^, M. L. Kirk*.

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A combination of electronic absorption, magnetic circular dichroism, and resonance Raman spectroscopies have been used to probe the excited state electronic structure of LWO(bdt) and LWO(tdt) (where L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate, bdt = benzene-1,2-dithiolate, tdt = toluene-3,4-dithiolate). These formally d1 oxo-W(V) ene-1,2-dithiolate complexes possess low-energy charge transfer transitions that have been assigned by comparison to their oxomolybdenum counterparts, LMoO(bdt) and LMoO(tdt). These S→M CT transitions serve as an important spectroscopic probe for determining the contribution of the metal to the electronic structure of these molecules. Specifically, metal ion dependent shifts in S→M dxy transitions probe the inherent valence ionization energy differences between oxo-W and oxo-Mo dithiolates. The results of gas-phase PES studies support the spectroscopic assignments and correlate well with observed differences in solution reduction potentials. We have also used charge transfer spectroscopy to estimate metal ion dependent activation energy differences for enzymatic oxygen atom transfer (OAT) process. Our studies strongly indicate differences in the rate of nucleophilic attack on the M≡O * orbital by strong oxo acceptors is not solely a function of the metal ion reduction potential, and OAT processes are modified by the degree of metal induced destabilization of the metal oxo π* orbital. We provide evidence that this effect is as important as reduction potential differences between Mo and W in affecting the rate of simple oxygen atom transfer. The following is taken directly from the unpublished paper that is however presented in my dissertation which is public, but should not be included directly in the present study as a matter of courtesy. The following syntheses and characterization is given below in order to give absolute credit to Dr. Young for his contributions to this wonderful chemistry developed by him and his research group, without which none of the present studies would have been possible. On this, if we do publish this paper (PES/XRD/DFT) it would be right to place him on the authorship as I could not have made these compounds without this guidance and insight. E.g. My initial attempts to make these dithiolenes was first attempted by using the above Tp*WOCl2 precursor with the dithiols/base and salts of the dithiolates with very little success. Note: the echem/ET rate of the tdt complex performed by Anne and published in ICA with due credit given w/r to references is a result of my synthesis following Dr. Youngs methods in general with slight modifications. The syntheses of these oxo-W dithiolates and associated precursors are described in a manuscript under preparation.46 However, in the absence of a published synthetic procedure for the {LWO}2+ species, the initial preparation46 and physical characterization46 (elemental analysis, electrochemical, mass spectroscopy, and EPR results) of these compounds to be published at a future date are therefore reported for further insight. Unless noted, all reactions and manipulations were performed under an atmosphere of dinitrogen using Schlenk or glove–box techniques. All solvents were dried, distilled and deoxygenated prior to use. The spectroscopic grade solvents (OmniSolv, EM Science) used in the solution spectroscopic studies (DCM/DCE/Benzene/Toluene) were distilled under a dry dinitrogen atmosphere and degassed by repeated freeze–thaw–pump cycling prior to use. The poly(dimethylsiloxane) mulling agent (PDMSO: Aldrich) used in the solid–state optical studies (EA/MCD) was degassed by consecutive freeze–thaw–pump cycles. Infrared grade KBr (Fischer) was used in the IR and Raman vibrational studies. The solid–state Raman experiments employed anhydrous NaCl, Na2SO4, and NaNO3 (Baker, A.C.S. reagent grade). The anhydrous salts and internal standards used in the solid–state infrared and resonance Raman studies were dried in vacuo at ~130C for 1.5 hours prior to sample preparation. Electrochemical experiments were performed using a Cypress Electrochemical System II with a 3 mm glassy carbon working electrode and platinum auxiliary and reference electrodes.46 Solutions of the complexes (1–2 mM) in 0.1 M NBu BF4 /acetonitrile were employed and potentials were referenced to internal ferrocene (E1/2= +0.390 V vs SCE). Potentials are reported relative to the Saturated Calomel Electrode (SCE). Chromatography was performed on 50 cm x 2 cm diameter columns using Merck Art. 7734 Keiselgel 60.46 Mass spectra were recorded on a Vacuum Generators VG ZAB 2HF mass spectrometer.46 Microanalyses were performed by Atlantic Microlabs, Norcross, GA.46 Syntheses.46, 49-53

An extensive range of oxo–Mo(V) compounds containing the hydrotris(3,5–dimethylpyrazolyl)borate ligand has been generated by metathetical reactions of LmoOCl2. The analogous oxo–W(V) complex is generally much less susceptible to ligand exchange reactions. However, the iodo complex, LWOI2 , is more amenable to derivitization albeit under forcing conditions. Its synthesis follows

29

a multi–step sequence beginning with NEt4 [LW(CO)3 ], which is prepared by the reaction of W(CO)6 with KL. Oxidation with iodine results in the generation of LWI(CO)3 which is thermally decarbonylated to reactive LWI(CO)2. Reaction of this complex with dioxygen results in the formation of the oxo(carbonyl)–W(IV) complex, LWOI(CO). Further oxidation with elemental iodine results in the generation of LWOI2 in modest overall yields. The reaction sequence can be performed in one pot from isolated LWI(CO)3. The complex may also be prepared, in ca. 80% yield, from the reaction of dioxygen with LWI2(CO); however, the current low yield synthesis of LWI2(CO) negates any overall synthetic advantage. Red LWOI2 reacts with sodium salts such as Na2bdt, Na2tdt, NaOPh, Na(o–OC6H4SEt) (etp) and NaSPh to produce derivatives of the type LWOX2 (X = OPh, etp, SPh; X2 = bdt, tdt). The reactions are perfomed at 60–70 °C in tetrahydrofuran or toluene. In the latter solvent, small amounts of 18–crown–6 must be added to assist the dissolution of the metal salt. The reactions are conveniently monitored by solution EPR spectroscopy or thin layer chromatography. Attempts to react free thiols or alcohols with LWOI2 in the presence of NEt3 produced no observable reaction. Our attention will focus only on the bidentate ligand complexes, LWO(bdt) and LWO(tdt). These complexes are air–stable in the solid-state, and are readily soluble in chlorinated solvents and tetrahydrofuran but only sparingly soluble in methanol and hydrocarbons. In all cases, an [M+] peak cluster was observed by mass spectrometry and satisfactory microanalyses were obtained.46 LWOI2. A solution of LWI(CO)3 (3.0 g, 4.4 mmol) was refluxed in tetrahydrofuran (50 mL) for 2 h to produce a solution of LWI(CO)2. The solution was then cooled and subjected with a slow flow of dioxygen gas. The generation of LWOI(CO) was conveniently monitored by solution IR spectroscopy. When a maximal concentration of LWOI(CO) was attained, the atmosphere within the flask was replaced with dinitrogen, iodine (0.6 g, mmol) was added, and the mixture was refluxed for 3 h. The solvent was then removed by rotary evaporation and the residue was column chromatographed on silica using 1:1 CH2Cl2/petroleum ether (60–80°). The red band was collected and recrystallized from CH2Cl2/MeOH. Yield 0.75 g (22%). Anal. Calc. C15H22BI2N6OW: C, 23.99; H, 2.95; N, 11.20. Found: C, 24.05; H, 3.03; N, 11.08. IR (KBr): 2962w, 2927w, 2561w, 1544s, 1445s, 1414s, 1383w, 1354s, 1202s, 1070s, 1039w, (W=O) 971s,

856w, 811w, 797w, 688w, 646w, 475w cm–1. UV–visible spectrum (CH2Cl2): max 464 (sh, 3520),

354 nm (sh, 5920 M–1 cm–1). Electrochemistry: E1/2 –0.98 V, Ipc/Ipa 1.00, Epp 53 mV (reversible reduction); E1/2 0.76 V, Ipc/Ipa 1.43, Epp 60 mV (quasi–reversible oxidation). LWO(bdt). A suspension of Na2bdt in toluene (15 mL) was prepared by the addition of sodium (32 mg, 1.34 mmol) to a solution of benzene–1,2–dithiol (95 mg, 0.67 mmol), followed by heating to reflux for 15 min. To the cooled suspension was added a solution of LWOI2 (0.50 g, 0.67 mmol) in tetrahydrofuran (15 mL). The reaction was heated at 60–70 °C for 1.5 h. The solvent was reduced to dryness under vacuum, the residue was dissolved in a minimum volume of dichloromethane, then column chromatographed on silica using dichloromethane/hexane (3/2) as eluent. The major bright green band was collected and the compound was recrystallized from dichloromethane/methanol. Yield 120 mg. Anal. Calc. C21H26BN6OS2W: C, 39.58; H, 4.11; N, 13.19; S, 10.06. Found: C, 39.31; H, 4.13; N, 13.03; S, 10.04. IR (KBr): 2560m, 1542s, 1443s, 1415s, 1381m, 1357s, 1272w, 1220m, 1196s, 1096w, 1075s, 1040m, 987w, (W=O) 949s, 873w, 857m, 810m, 788m, 749m, 690m, 645m, 471m cm–1. UV–visible spectrum (CH2Cl2): max 554 ( 1800), 435 nm (sh, 2660 M–1 cm–1). EPR (25 °C, CH2Cl2): <g> 1.8907. EPR (77 K, CH2Cl2/toluene, 1/1): g1 1.9593, g2 1.8949, g3 1.8169. Electrochemistry: E1/2 –0.96 V, Ipc/Ipa 1.02, Epp 72 mV (reversible reduction); Epa 0.49 V (irreversible oxidation). LWO(tdt). A mixture of LWOI2 (350 mg, 0.46 mmol) and toluene–1,2–dithiol (72 mg, 0.46 mmol) in tetrahydrofuran (15 mL) was heated to 50 °C, then ammonia gas was passed slowly through the solution for 10 mins. The reaction was allowed to stir for a further 15 mins and the solvent was removed by rotary evaporation. The residue was dissolved in a minimum volume of dichloromethane, then column chromatographed on silica using dichloromethane/hexane (3/2) as eluent. The main bright green band was isolated and the compound was recrystallized from dichloromethane/methanol. Yield 180 mg.

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Anal. Calc. C22H28BN6OS2W: C, 40.57; H, 4.33; N, 12.90; S, 9.84. Found: C, 40.37; H, 4.24; N, 12.79; S, 9.70. IR (KBr): 2553m, 1544s, 1451s, 1415s, 1384m, 1360s, 1262m, 1202s, 1071s, 1041m, (W=O)

941s, 858m, 806m, 690s, 650m, 472m cm–1. EPR: <g> 1.889 UV–visible spectrum (CH2Cl2): max 505 (sh, 4410), 475 (sh, 4950), 310 nm

( 9200 M–1 cm–1). EPR (25 °C, CH2Cl2): <g> 1.8889. EPR (77 K, CH2Cl2/toluene, 1/1): g1 1.9627, g2 1.8942, g3 1.8115. Electrochemistry: E1/2 –0.93 V, Ipc/Ipa 1.02, Epp 70 mV (reversible reduction); Epa 0.43 V (irreversible oxidation).

Room temperature infrared (IR) vibrational spectra between 300 – 3,000 cm–1 were recorded at both 1.0 and 4.0 cm–1 resolution as pressed KBr disks on a BOMEM MB–100 FT–IR spectrometer equipped with a N2 purged sample chamber. The vibrational bands (2850, 1603, and 906 cm–1) of a standard polystyrene thin film were used as a frequency calibrant. The IR spectra are useful for detecting trace quanities of the LMoOCl2 and LWOI2 precursors, which respectively may be present in the LMoO(S-S) and LWO(S-S)

samples as a residual contaminant.46

The IR spectra were thus utilized to monitor the purity of the Mo and W dithiolate compounds, as indicated by the absence of the 961 cm–1 Mo≡O and 971 cm–1 W≡O vibrational stretching modes associated with the respective LMoOCl2 2 and LWOI2 precursor complexes. The following is from the complimentary study to the oxo-Mo analogs presented above under Dr.Kirk in collaboration with Dr. Young where the syntheses would have appeared for these oxo-W complexes. EA, MCD and rR spectroscopies have also been used to probe the electronic structure of LWO(bdt) and LWO(tdt). This work is important for determining the contribution of the metal (Mo vs. W) on the electronic structure of these systems. These results have been related to the inherent reactivity differences between pyranopterin Mo and W enzymes, as well as small molecule oxygen atom transfer catalysts. These studies have shown that inherent metal dependent differences in the rate of nucleophilic attack on M≡O by strong oxo acceptors are not solely a function of the reduction potential, but are modified by the degree of metal induced destabilization of the M≡O π* acceptor orbital. This effect is as dominant as the reduction potential differences between Mo and W in affecting the rate. (Tp*)MoNO(bdt) (1)/(Tp*)MoNO(tdt) (2) / (Tp*)MoNO(bdtCl2) (3); synthesis/isolation/purification/general characterization/ specific characterization, XRD of all 3 complexes; 1 and 3 new models; 2 previously reported by J. McCleverty, 2 and 1 were synthesized and purified by modified procedures to that previously reported for these in IKD dissertation (bdt new complex), as was the new compound 3 (1st time here by JS). The syntheses of the precursors Tp*MoNO(CO)2 and Tp*MoNOI2 were carried out by J. Schirilin who did an outstanding job as an undergraduate, the modified syntheses and new purification procedures for these type of dithiolene complexes were developed by both JS and FEI. JS synthesized complex 3 and characterized (IR,MSNMR), FEI dev purification procedure using a combination of TLC profiling,extraction, multiple collums, and recrystallization for obtaining suitable crystals for XRD for 3 and ultra pure compounds for detailed spectroscopic/electrochemical studies (rR,EA,CV, and 1e- reduction by cobaltocene to generate EPR species and to try and crash out this species as a salt), HKJ refined crystal structures of new bdtCl2 complex and resolved the bdt compound originally synthesized and solved by IKD (IKD also did the tdt structure (tdt first synth by McCleverty, Note: this is the only tdt structure known for any of the Tp*ME(S-S) system types). Also note that BW did HeI/II/NeI on Tp*MoNO(tdt) and compared to the oxo-Mo and sulfido-Mo tdt analogs. JS did HeI/HeII on the Tp*MoNObdtCl2 complex, which was later redone by HKJ? including closeups?. I later supplied Tonya Bill the highly purified bdt complex for HeI PES. The combined efforts by JS/FEI in purification are important, as the previous methods reported did not produce ultra pure samples necessary for further optical and spectroscopic studies extremely sensitive to trace contaminants (e.g. rR ,EA) that had not been reported for these compounds. While suitable single crystals could be isolated from previous methods, the impurities in these complexes prepared in this manner, which were not exhibited by TLC under these conditions were evident in the PESand CV characterization. Depending on the nature of the impurities

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NMR and IR were also useful probes (for identifying traces of initial precursors). However, additional species/decomposition products do interfere in other char techniques such as abs/raman complicating the spectra. Initiating a more rigorous TLC profilewith various combination and types of different solvents/ and multiple separation techniques provided the conditions needed to remove these impurities to obtain pure samples for further study. The previous methods were inadequate as evident by the first raman/ CV studies which showed these impurities. All reactions were carried under argon atmosphere by using standard Schlenk techniques and standard glovebox techniques. THF and hexane were distilled from NaK/benzophenone; triethylamine was distilled from NaK, toluene was distilled from Na. All solvents were thoroughly degassed by freeze, pump, and thaw cycling three times. H2tdt (Aldrich) were used as received. IR were taken as KBr discs using a Nicolet Avatar 360 FTIR spectrometer. Procedure: Diiodonitrosyl{tris(3,5-dimethylpyrazolyl)hydroborato}molybdenum(III), the starting molecule for all of our reactions was synthesized according to McCleverty's preparation of molybdenum (III) compounds1. The precursor of the diiodo complex, Mo[HB{C3H(CH3)2N2}3](CO)2NO (1) dicarbonylnitrolsyl{tris(3,5-dimethylpyrazolyl)borato}molybdenum(III) was synthesized as follows: In a glove box, under nitrogen, were mixed in a 300 ml round bottomed flask K[HB{C3H(C3H(CH3)2N2}3 (10 g) (23.81 mmol) and molybdenum hexacarbonyl (Mo(CO)6) (6.30 g) (23.87 mmol) in about 120 ml of freshly distilled THF. The mixture was then moved out of the glovebox and put onto a Schlenk line where it was refluxed and stirred under constant argon flow overnight. The yellow suspension was left to cool down. Once the mixture had reached room temperature, glacial acetic acid (4.5 ml) was added and stirred for 1.5 hours. While this mixture was stirred, a solution of N-methyl-N-nitroso-p-toluene sulfonamide (6.67 g) dissolved in freshly dried THF (30 ml) was prepared. This was the source of the nitric oxide. This solution was then added to the 300 ml round bottomed flask reaction mixture and stirred at room temperature overnight, under a constant argon flow. Since the final product, Mo[HB{C3H(CH3)2N2}3](CO)2NO, is not air sensitive, the extraction of the orange solution was performed in the air. First, the THF solution was evaporated to dryness using a rotary evaporator, leaving at the bottom of the flask an orange solid. The solid was then dissolved in about 200 ml of chloroform. To remove most of the undissolved toluene sulfonamide, the suspension was filtered over a 4-cm diameter frit funnel topped with about 4 cm of celite. The celite layer was renewed for every 25 ml of solution that went through. All the chloroform was removed using a rotary evaporator. The crude orange solid was then washed three times with ethanol (3 x 75 ml ) and dried to give 9.15-10.05 g of bright orange solids. (79-87 % yield). FTIR (KBr): υNO 1653 cm-1, υCO

1902 cm-1, 2007 cm-1 υBH 2545 cm-1. H1 NMR 200MHz in CDCl3: Pyrazole protons: δTMS=5.83 (2), 5.73 (1), methyl protons: δTMS=2.46 (6), 2.35 (6), 2.34 (3), 2.32 (3). Mo[HB{C3H(CH3)2N2}3]I2NO. (LMo(NO)I2) (2). Iodine (2.60 g) (10.24 mmol) was added to a 50 ml round-bottomed flask containing Mo[HB{C3H(CH3)2N2}3](CO)2NO (5.0 g) (10.44 mmol) in 100 ml of dry cyclohexane. The solution was refluxed for approximately 72 hours. The resulting black solution was then left to cool to room temperature. The product was isolated by filtration and recrystallized from hot dry toluene; 4.21g-5.41 of fine black crystalline material were recovered (59-80% yield). IR spectrum on KBr disc: υNO 1701 cm-1, υBH 2553 cm-1. H1 NMR 200MHz in CDCl3: Pyrazole protons: δTMS=6.10 (1), 5.86 (2), phenyl protons: δTMS=7.13, 7.25 (5), methyl protons: δTMS=2.78 (3), 2.58 (3), 2.29 (6), 2.20 (6). Mo[HB{C3H(CH3)2N2}3](NO)S2C6H4. (LMo(bdt)(NO))(3). In a 50 ml round bottomed flask, were mixed LMo(NO)I2, (0.5 g)( 0.73 mmol), 1,2 benzenedithiol (0.2 ml) (1.74 mmol) and freshly distilled dry triethylamine (0.3 ml; to deprotonate the dithiol). The reaction was refluxed in dry toluene (15ml) overnight under argon gas flow. Important observation: right after the addition of triethylamine the color of the solution changed to a deep blue. Once the solvent was evaporated the remaining solid had a really dark color really closed to black. The compound was purified by column chromatography on silica gel using 2/1 Cyclohexane/methylene-chloride as the eluent. 0.38 g of LMo(bdt)(NO) was recovered (91% yield). Theoretical true mass: 565.0792 m/z, observed true mass: 565.0798m/z. IR spectrum on KBr disc: υNO 1670 cm-1, υBH 2552 cm-1.

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H1 NMR 200MHz in CDCl3: Pyrazole protons: δTMS=6.02 (2), 5.65 (1), phenyl protons: δTMS= dd 8.11, dd 7.29 (2), methyl protons: δTMS=2.53 (6), 2.46 (3), 2.44 (3), 2.31 (6). Mo[HB{C3H(CH3)2N2}3](NO)(S2C6H4Cl2) (LMo(bdtCl2)(NO)) (4). In a 50 ml round bottomed flask, 1 g (0.369 mmol) of LMo(NO)I2, 0.340 g (1.61 mmol) of 3,6-dichloro-1,2-benzendithiol and about 0.5 ml of freshly dried triethylamine were refluxed in about 50 ml of dry toluene overnight under argon gas flow. Important remark: right after the addition of triethylamine the solution changes to a greenish color, later becoming deep blue. The triethylamine salt was removed by filtration and the solution was evaporated to dryness in presence of silica with a rotary evaporator. The compound was purified by chromatgraphy on silica gel using 2/1 cyclohexane/methylene-chloride as the eluent. 0.75-.80g of LMo(bdtCl2)(NO) are recovered as a dark purple solid, or a deep blue solution. Theoretical true mass: 633.0002 m/z, observed true mass: 633.0035 m/z. IR spectrum on KBr disc: υNO 1674 cm-1, υBH 2548 cm-1. H1 NMR 200MHz in CDCl3: Pyrazole protons: δTMS=6.04 (2), 5.66 (1), phenyl protons: δTMS= 7.40 (2), methyl protons: δTMS=2.51 (6), 2.43 (3), 2.33 (6), 2.18 (3). Mo[HB{C3H(CH3)2N2}3](NO)(S2C4N2H2C4H4). (LMo(qdt)(NO))(5) This synthesis was done following the same main step used for the LMo(bdt)(NO) compound. In a 50 ml round bottomed flask with 15 ml of toluene, 0.5 g (0.739 mmol) of LMo(NO)I2, 200 mg (1.031 mmol) of qdt dithiol and about 0.3 ml of triethylamine to deprotonate the thiol that were refluxed in dry toluene overnight. This was done under argon gas flow. The solution turned to a dark blue. A small amount of the solid left inside look reddish brown with some yellow green color on the side of the flask. The solid was kept under argon atmosphere. Once it was run through a column the product shown by mass spec was lost. The column might have to be run in the future under constant argon pressure with degassed solvent. From a TLC plate a good solvent pair seems to be hexane/methylene-chloride 4/1. Mass spec is the only characterization that we have, ran on impure solution. This reaction was ran 2 more times, and each time the product was lost. Might consider the solubility of the qdt product, are we losing it with ppting/filtering prior to adding to collumn? Or are we losing on collumn using silica gel as it may protonate a N on the qdt ring, which makes it insoluble in the organic solvents employed before it can be eluted off, thus may consider that protonation in qdt complexes is reversible and maybe might try base (TEA) to keep the eluting solvent basic for chromatography. I have seen the use of TEA on a collumn, but this has yet to be applied in our case. Mo[HB{C3H(CH3)2N2}3](NO)(S2C6H4CH3) (LMo(tdt)(NO)). In a 50 ml round bottomed flask, 0.250 g (0.369 mmol) of LMo(NO)I2, 0.055 g (0.554 mmol) of toluenedithiol and about 0.5 ml of freshly dried triethylamine were refluxed in about 50 ml of dry toluene overnight under argon gas flow. As in all of the reaction, right after the addition of triethylamine, the solution changes color, to a greenish color, later becoming deep blue. The triethylamine salt was removed by filtration and the solution (purple/black) was evaporated. The solid recovered was purple. In solution the (LMo(tdt)(NO)) decomposed in the air more readilly than the bdt and bdtCl2 complexes as observed by it turning black in a short time. Also, if these compounds are not purified properly, they appear to decompose more readily evident by discoloration and clear salts forming with solvation. Using a uv lamp, components not previously visible are revealed, and these must be removed, as the following method does, otherwise the previous decomposition behavior will occur. The purification of the tdt complex was obtained by the following method in Note: Note: After the initial purification, a combined set of collumns 1:1 and 1:3 DCM/cyclohexane under Ar with TLC profiling and pooling the pure fractions collected in test tubes provided the ultra pure complexes (evident by TLC/NMR/IR/MS) as needed immediately prior to a study; these I supplied to Anne for her more detailed CV studies w/r to ET rates reported in a later paper and in her dissertation. This method provided a means to remove decomposition products/and precursors and ensure the purity of the sample. NMR and IR are important for identifying any trace amts of initial Tp*MoNO(CO)2 and Tp*MoNO(I)2 precursors present (the iodo precursor is easily removed from target by these collums; thus need to make sure halide complex pure before reaction via TLC/IR/NMR/MS). EPR of isolated targets revealed no signal, thus no paramagnetic contaminants/decomposition products/ or 1e- ox/red species of target; that supports the expected e- formulation of the mononuclear complex and it being diamagnetic (consistent with ability to generate NMR spectrum, and subsequent identification of target and absence of any other diamagnetic species). Note: CV and rR are sensitive to the presence of other {Tp*MoNO} species. EA of

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the targets and precursors are distinctly different. Can we identify decomposition products/fragments that may occur in presence of water/oxygen? How does EA look like with such exposure? Mo[HB{C3H(CH3)2N2}3](NO)(O2C2H4) (LMo(ethanediol)(NO)). In a 50 ml round bottomed flask, 0.250 g (0.369 mmol) of LMo(NO)I2, 0.033 g (0.554 mmol) of H2EDO and about 0.5 ml of freshly dried triethylamine were refluxed in about 50 ml of dry toluene overnight under argon gas flow. As in all of the previous reactions, right after the addition of triethylamine, the solution changes to deep red. The triethylamine salt was removed by filtration and the solution was evaporated under Ar. MS (ESI) identified target from crude product/ red-pink-orange solid. Samples in glove bag were tested for extraction/ppt out components by extracting two separate samples of the dry residue with Tol and DCM, each solution filtered through a pasteur pipette containing a plug of glass wool, conc, followed by layering n-pentane on top of both filtrates. Also I found by TLC that Tol:DCM 1:1 would effect efficient separation of components (~7) that could each be pulled separately off collumn and identified by MS. This was not pursued further, but sample is still availlable for isolating target. The syntheses and characterization of these 3 complexes were first presented at the ACS 2001 meeting and subsequently reported in the following paper. These synthetic procedures are primarily taken from the experimental results of JS/FEI/IKD on the study of various {Tp*MoNO}2+ complexes, in addition to those methods reported for general/optimized Ops in the Tp*MoO(bdtCl2) paper described above, and thus are shown as is. Note: HKJ provided assistance with the qdt complex syntheses in addition to refining crystallographic data for the bdtCl2 complex, as well as re-refining the structure of bdt complex, which was initially synthesized ,collected and solved by IKD(who also solved tdt structure, both bdt(new synth) and tdt structures reported in IKD dissertation; synth of both in IKD diss. followed a modification of tdt synth first reported by McCleverty). The synth, isolation and purification of these 3 complexes in ACS abstract and later publication below (bdtcl2/bdt/tdt) derive from modifications developed experimentally by FEI/JS w/r to the Mcleverty paper (tdt) and subsequent modifications to this initial tdt synth made by IKD in his dissertation(bdt/tdt). ACS 2001 SanDiego, INOR 505 The Molecular Structure, and Properties of Molybdenum Nitrosyls with Ene-1,2-Dithiolate Ligands. Julien T. Schirlin, Frank E. Inscore, Hemant K. Joshi, Ish K. Dhawan, and John H. Enemark. The complexes LMoNO(bdt) and LMoNO(qdt)have been synthesized and physically characterized (where L=hydrotris(3,5-dimethyl-1-pyrazolyl)borate,bdt=benzene-1,2-dithiolate, qdt=quinoxaline-2,3-dithiolate). These diamagnetic compounds with a vacant dxy orbital show significant perturbation of the Mo-S bonding relative to their structurally defined oxo-Mo counterparts, LMoO(bdt) and LMoO(qdt). For example, the crystal structures of LMoO(bdt) and LMoNO(bdt) show that the fold angle between the S-C=C-S and S-Mo-S planes is ~20 ° greater for LMoNO(bdt). The reduction potentials for these nitrosyl complexes indicate that it should be possible to isolate the one-electron reduced paramagnetic [LMoNO(ene-1,2-dithiolate)]- species. These reduced complexes are formally d5 and contain a single electron in the dxy orbital, analogous to the well-known d1 species, LMoO(ene-1,2-dithiolate), that have been extensively characterized by electronic absorption, magnetic circular dichroism, and resonance Raman spectroscopies. Note: It was at the ACS that the XRD/syntheses/MS,NMR(H,C),IR/CV/Abs/rR/HeI/IIPES of the bdtCl2 was 1st presented (synth by JS,;purified and crystals grown by FEI). The XRD was refined by Hemant, who also re-refined the bdt structure of IKD, the tdt structure of IKD was also presented (see IKD diss). HeI/II PES by JS was compared to tdt complex (HeI/II/NeI PES of Tp*MoNOtdt reported previously by BW/JHE). Initial DFT calcs by JS were applied to simplified NH3/edt species to probe folding as function of energy and optimal angle. It was here that we were setting up the origin of the fold angle, and how the electronic structure differences in oxo vs NO systems were being addressed w/r to observed angle differences and their relation to dithiolate buffering effect(see DBE in BW Pes paper). Also, the data I aquired w/r to the CV,EA,rR on the bdt ,tdt and bdtCl2 complexes were also compared here for the 1st time. Preliminary/specific metric data from my oxo-bdtcl2 study (in prep) and that reported for oxo-bdt by IKD/JHE were used for comparison purposes to point out the effect that the axial group (oxo vs NO) and hence e- occupation has on these

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parameters and relation to electronic structure. The most significant change was in the E-M-S and fold angle w/r to axial group. Note: My interest in the fold angle observed in these NO complexes and their oxo –Mo analogs w/r to diffs-effects-relationships on M-S bonding/electronic structure and contributions to reactivity in enzmes, began initially in my dissertation , and was pursued further upon my joining JHE group as evident by the NIH proposal I wrote shown below. Julien, who was making precursors of MoNO, was doing this initially for diamagnetic host for oxo-Mo analogs in single crystal epr studies. However, we immediately changed direction regarding these sytems as evident, and this project under my guidance served as the focus of his UG Honors theses. A lot of insight and postulates came out of these early studies that has catalyzed subsequent studies. Hemant , who was initially working on other projects, served as the groups XRD data collector, and thus refined all of our crystal structures obtained. After JS left, Hemant was later coupled into these NO-Mo/O=Mo studies, providing him a research project and materials for his dissertation. He has become active in obtaining PES data and DFT calcs. The combined efforts of all here is starting to payoff. Hemant, who has been my protégé, and under my direction and many discussions is now very capable and knowledgeable w/r to these studies, will be pushing this effort forward now as I am about to leave, and will be responsible for these ongoing studies in progress. I hand the torch to him as he has earned it, we were a very effective and productive team. ICA paper 2002 Six-Coordinate Molybdenum Nitrosyls with a Single Ene-1,2-Dithiolate Ligand Hemant K. Joshi, Frank E. Inscore, Julien T. Schirlin, Ish K. Dhawan, Michael D. Carducci, Tonya G. Bill and John H. Enemark* All reactions and manipulations were carried out under an inert environment of argon gas using standard Schlenk techniques, a high-vacuum/gas double line setup, and an inert atmosphere glove bag. The argon was predried by passing the high-purity-grade gas through a series of drying towers. All glassware was dried in an oven at 150°C and Schlenk ware was further purged by repeated evacuation and inert gas flushes prior to use. Tetrahydrofuran (THF) and toluene were distilled from Na/benzophenone; triethylamine was distilled from Na/K amalgam [38]. The prepurified solvents were subsequently transferred and stored under N2 over fresh drying agents. These solvents were freshly distilled under nitrogen prior to use, thoroughly degassed by repeated freeze-thaw-pump cycles, and transferred to reaction vessels via steel cannulae under a positive pressure of inert gas. Dichloromethane, 1,2-dichloroethane (DCE), cyclohexane, toluene (EM Science, Omnisolv), n-hexane and n-pentane (Burdick and Jackson) were used as received and deoxygenated by bubbling with argon. Molybdenum hexacarbonyl (Mo(CO)6, Aldrich) was dried in vacuum prior to use. Potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate (KTp*), the precursor complexes (Tp*)MoV(NO)(CO)2 and (Tp*)MoV(NO)I2.C6H5CH3 and the ligands H2bdt (1,2-benzenedithiol) were prepared according to literature procedures [39-41]. The ligand H2tdt (4-methyl-1,2-benzenedithiol) and H2bdtCl2 (3,6-dichloro-1,2-benzenedithiol) employed in the syntheses of the (Tp*)MoV(NO)(S-S) compounds (2, 3) were used as received from Aldrich. TLC analysis was carried out on silica gel 60 F254 plastic sheets (EM Science) and column chromatography was carried out in glass columns with silica gel (Merck, grade 9385, 230-400 mesh, pore diameter 60 Å) as the stationary phase. Mass spectra were recorded on a JEOL HX110 high-resolution sector instrument utilizing fast atom bombardment (FAB) ionization in a matrix of 3-nitrobenzyl alcohol (NBA). IR spectra (4000-400 cm-1) were collected on a Nicolet Avatar ESP 360 FT-IR spectrophotometer in KBr disks or as dichloromethane solutions (between NaCl plates) at room temperature. Electronic absorption spectra of samples dissolved in 1,2-dichloroethane solutions were recorded with a 1-cm pathlength Helma quartz cell equipped with a teflon stopper, on a Cary 300 (250-900nm) spectrophotometer. Solvent background corrections were made in all cases. 1H-NMR (CDCl3) spectra were acquired on a Bruker DRX-500 spectrometer operating at a 1H frequency of 500.13 MHz using a 5 mm Nalorac triple-resonance 3-axis gradient probe. Chemical shifts were referenced to residual CHCl3 at 7.24 ppm.

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Synthesis of (Tp*)Mo(NO)(bdt) (1)The synthesis of (Tp*)Mo(NO)(bdt) (1) reported here, has been modified from that previously published [4], and provides an optimized method to obtain very pure samples. In a 100 ml round bottom evacuated Schlenk flask, highly purified (Tp*)Mo(NO)I2·C6H5CH3 (0.38 g, 0.5 mmol) was added to H2bdt (0.1 g, 0.7 mmol) in 50 ml of dry, degassed toluene in a 100 ml round bottom Schlenk flask for synthesis of 1. The mixture was deoxygenated thoroughly with argon saturation while being stirred at ~80°C. Dry, degassed Et3N (0.4 ml, 2.2 mmol) was added slowly dropwise via a gas tight syringe to this rigorously stirring solution. The solution changed color to greenish and later to deep blue. The reaction mixture was refluxed for 16 hours, and the reaction progress was monitored by IR spectroscopy (shift of <(NO) stretching frequency) and TLC analysis (disappearance of (Tp*)MoV(NO)I2 precursor). Upon completion of the reaction, the blue-green precipitate, primarily Et3N×HI resulting from the proton abstraction and ligand exchange processes, was removed by filtration from the hot solution under dry argon. The filtrate was cooled to room temperature and evaporated to dryness with a rotorary evaporator. The solid dark-purple residue was re-dissolved in toluene, concentrated under vacuum, and layered with n-pentane. The dark-purple powder precipitate was collected by filtration and washed with n-pentane until the filtrate was clear. The powder was then dissolved in dichloromethane, filtered to remove any insoluble materials, and evaporated to dryness in vacuum. The solid was pumped on for several hours to assure dryness and the complete removal of excess triethylamine. The solid material was re-dissolved in dichloromethane, concentrated, and loaded on a silica gel chromatographic column under a positive pressure of argon. A dark-purple fraction (band #1) eluted off the column using dichloromethane: cyclohexane (1:3) as the eluant. Band #1 was further purified by a second silica gel column using dichloromethane: cyclohexane (1:1) as the eluant. The purity of compound was confirmed by TLC analysis. The dark-purple solution, which was deemed pure by TLC was evaporated to dryness in vacuum, re-dissolved in dichloromethane, and layered with n-pentane to yield a dark -purple crystalline material. This material was filtered, washed with pentane and then dried in vacuum. The product was characterized by IR, UV/VIS and mass spectroscopy. Slow vapor diffusion of n-pentane into a saturated dichloromethane solution of 1 afforded diffraction quality crystals. Characterization: HRMS [M + H]+ peak gives m/z = 565.0798 (calculated, 565.0792) and corresponds to the formula [12C21H27N711B32S235O98Mo], IR data (KBr) n(B-H) = 2551 cm-1, <(NO) 1670 cm-1, UV-vis data (in DCE) 8(nm)(,(M-1cm-1)): 732(1576), 579(4527), 370(3154), 326(3645), 292(5898), 1H-NMR (500MHz, CD2Cl2, 298 K): *(ppm) 8.057, 7.274 (2H, dd, 3JHH = 4.5Hz, 3.0 Hz; 2H, dd, 3JHH = 4.5Hz, 3.0 Hz), 5.992, 5.623 (2H, s; 1H, s), 2.485, 2.404, 2.308 (7H, s; 4H, s; 7H, s). The preparation of (Tp*)MoNO(tdt) (2) followed from published procedures [19]. A mixture of (Tp*)Mo(NO)I2·C6H5CH3 (0.9 g, 1.2 mmol) and H2tdt (0.33 g, 2.1 mmol) were refluxed for 16 hours instead of 24 hours as given in the literature [19]. Slight modifications were also made in the work up procedures to obtain the pure compound suitable for growing X-ray diffraction quality crystals. In our work-up procedure the reaction mixture was evaporated to dryness under reduced pressure and the solid obtained was dissolved in a 1:3 CH2Cl2:cyclohexane mixture and subjected to column chromatography. The product is contained in a deep blue band that is well separated from other side products, which do not separate well when eluted with CH2Cl2 as in the original preparation [19]. Further purification was achieved by a second column chromatography step using 1:1 CH2Cl2 : cyclohexane as the eluant. Slow diffusion of heptane into a CH2Cl2 solution of 2 yielded X-ray diffraction quality crystals. Highly purified samples of compound 2 employed in the spectroscopic and electrochemical characterization were obtained by methodology discussed above for compound 1. Compound 2 reveals similar spectroscopic features to those reported in the literature [19]. Synthesis of (Tp*)Mo(NO)(bdtCl2) (3) All the synthetic steps were similar to those described for 1, except for the stoichiometric ratio of the reagents. Highly purified (Tp*)Mo(NO)I2·C6H5CH3 (677 mg, 1.00 mmol) was added to a solution of H2bdtCl2 (220 mg, 1.1 mmol) in 50 ml of dry, degassed toluene in a 100 ml round-bottom Schlenk flask. Characterization: HRMS [M + H]+ peak that gives m/z = 633.0035 (calculated, 633.0002) and corresponds to the formula [12C21H25N711B32S235Cl2O98Mo] for 3, IR (KBr) n(B-H) = n(B-H) = 2548 cm-1; <(NO) 1674 cm-1, UV-vis data (in DCE) 8(nm)(,(M-1cm-1)): 739(1583), 573(6476), 372(3734), 330(5186), 294(8477). 1H-NMR (500MHz, CD2Cl2, 298 K): *(ppm) 7.369 (1H, s), 6.017, 5.629 (2H, s; 1H, s), 2.502, 2.415, 2.287 (7H, s; 4H, s; 7H, s).

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Note: I have rR(solid/solution) (in JHE group at Kirk facility) and EA(DCE/epsilons) of these 3 NO complexes. I am also and have been in the process of trying to generate 1e- reduced species using [Cp2Co] as chemical red agent (which is possible as it has more neg reduction potential than the MoNO complexes; where neutral cobaltocene is oxidized to cobaltocennium cation, which is concommitant with 1e- reduction of neutral M(II) to Mo(I) monoanion and therefore this cation may then serve as the counterion for potential crashing out of this reduced MoNO anion as a salt ) and subsequently char by EPR and also crash out as a cobaltcenium salt for char (structure/electronic) as the e- now resides in dxy orbital as in analogous Mo(V) complexes. Another system to probe S-Modxy CT is thus provided. See NIH Propsal I wrote in past with JHE detailing this below. Also note that this was the starting point and initial point of interest in JHE group for probing contributions to and effects of dithiolene folding ( along S---S axis ) on electronic structure and reactivity and implication to enzyme active site structure/reactivity during catalysis. It was first observed and commented on in the XRD for both the Tp*Mo(V)Obdt (pub/diss by IKD )and Tp*Mo(II)NObdt (diss IKD) where it was initially not thought to be important as it was ascribed to being the result of steric interactions. However, in FEI diss, based on observed folding and detailed studies of E=M-S bonding and electronic structure, the importance of this distortion and overlap considerations w/r to M-S covalency and impact on defining electronic structure was first proposed and discussed (see FEI diss) and thus provided the motivation to study such an effect in this type of system and how this might play a role in pyranopterin Mo/W enzymes. Note: the initial CV potentials of these 3 NO complexes in DCE were first obtained by myself under the direction of Anne Mc. These were later resynthesized by me and remeasured by anne for an additional paper, but still consistent with those published in this subsequent paper below where Anne focused on Het. ET rates. Exerpt from FEI Dissertation published on dithiolate folding: May 2000 In summary, the O-Mo-S angular distortions with respect to cis geometry, the stereochemical restrictions imposed by the ene-1,2-dithiolate chelate, the degree of saturation in the dithiolate chelate ligand skeleton, and the effect of the S---S fold angle are important structural factors to consider as they are postulated from these studies to exert considerable influence upon the nature and the extent of specific ligand-metal bonding interactions, and hence on the electronic properties of S→Mo CT. These factors are proposed to play an important role in determining how the pyranopterin dithiolene chelate is capable of interacting with the redox active orbital (dxy )on the Mo(V) center. Specifically, these factors influence the orientation of the sulfur 3p AO’s localized on the dithiolate chelate relative to the Mo d-orbitals. Therefore, this study is directed towards developing insight into those key factors which affect Mo (dxy ) – dithiolate (S p) orbital overlap and covalency. Of particular significance is the presence of a single terminal oxo ligand, which forms a very strong Mo≡O bond as evident by the short bond length (1.67-1.69 Å, relatively invariant within oxo-Mo-dithiolates), that severely destabilizes certain Mo d-orbitals such that the dxy orbital is lowest in energy and oriented orthogonal to the Mo=O bond vector. Thus, the O-Mo-S angle can affect the degree of specific Mo-S interactions, which are monitored by the corresponding CT energies and intensities. Electronic absorption spectroscopy can also be used to probe the intensity of CT bands as a function of the effects of the S-C=C-S unit on Mo-dithiolene bonding which are present to varying degrees in the complexes listed in Tables 1 - 3. The effects of conjugated (C=C) versus non-conjugated (C-C) bonding within the chelate ring on S – Mo bonding are to a first order modeled respectively by the dithiolene complexes LMoO(bdt), LMoO(tdt) and LMoO(qdt) with unsaturated 5-membered chelate rings, and by the dithiolate compounds LMoO(edt), LMoO(pdt) and LMoO(budt) with saturated 5,6, &7- membered chelate rings (Tables 1-2). The rotation of the two S 3p orbitals, which form two sets orthogonal to the C-S bond are not as restricted in the dithiolates as they are in the ene-1,2-dithiolate and as a result may possess different types of Mo-S orbital overlaps. These effects are important as it is not

37

known if the degree of saturation in the dithiolene linkage changes during the course of catalysis. The oxidation state (s) of the pyranopterin cannot be determined by X-ray diffraction, since at the resolution of the enzyme crystal structures, determination of C-C single versus double bonds in the dithiolate and/or pterin unit is not possible. The considerable ability of the Mo dithiolate chelate ring on constraining the orientation of the S 3p orbitals is examined by comparing to LMoO(SPhMe)2 which possesses monodentate thiolate coordination and less hindered rotation of the two S p orbitals orthogonal to the C-S bond. The angle about the S---S fold between the S-Mo-S plane and the dithiolene S-C=C-S plane is anticipated to play an important role in modulating the Mo (dxy ) – dithiolate (S p) orbital overlap. The situation where the dithiolate ligand and MoS2 planes are coplanar, good orbital overlap between specific Mo (4d) and dithiolate (S 3p) orbitals may not be as attainable as when the ligand folds relative to the S-Mo-S plane. Thus by folding about the S---S axis, the dithiolene ligand could possibly achieve more stabilizing interactions with the Mo d-orbitals. Therefore, changes in the orbital overlap between the redox active acceptor orbital (Mo dxy) and the dithiolate sulfur donor ligand orbitals resulting from changes in bonding and coordination geometry can affect the relative orbital energies and the extent of covalent interactions between these orbitals. Hence, these critical factors may play a potentially significant role in modulating reduction potentials and promoting ET regeneration in the enzyme active sites. Excerpt from FEI NIH proposal in collaboration with JHE; Electronic Effect of the S---S Fold Angle on Mo-S Bonding : submitted Aug 2000 A significant perturbation to Mo-S bonding involving the ene-1,2-dithiolate chelate was observed during the course of X-ray diffraction structural studies of (L-N3)MoIINO(bdt), the isostructural analogue employed as the diamagnetic host in the single crystal EPR studies of (L-N3)MoVO(bdt).58 The structures of (L-N3)MoVO(bdt) and (L-N3)MoIINO(bdt) depicted in Figure 2b, both show that the benzenedithiolate ligand is non-coplanar with the Mo atom. However, the crystal structural results clearly show that the angle formed between the ene-1,2-dithiolate S-C=C-S plane and the S-Mo-S plane along the line of intersection containing the S---S atoms is very different between the two complexes.32,58 This S---S fold angle (δ) is depicted in Figure 3a. The deviation from planarity is greater for (L-N3)MoIINO(bdt) (δ = 137.6°) than for (L-N3)MoVO(bdt) (δ = 158.7°). The S---S fold results in the ene-1,2-dithiolate plane (S-C=C-S plane) being distorted toward the terminal axial ligand (E = O, NO) in both structures. From an electronic structure point of view, this large difference in the S---S fold angle would be anticipated to have a significant effect on the in-plane Mo dxy – Spπ bonding scheme previously described from spectroscopic studies carried out on (L-N3)MoVO(bdt).22 Therefore, the magnitude of this angle would certainly dictate to an extent the degree of in-plane overlap between the Mo dxy and Spπ orbitals. The implications regarding this fold angle are highly suggestive that it may play a significant role during enzyme catalysis by defining a regulatory function for the pyranopterin-dithiolate. Hence, we hypothesize that changes in this fold angle that may occur during enzyme turnover, may play a regulatory role in fine-tuning reduction potentials and acting as a switch in gating electron transfer by controlling the extent of the in-plane Mo dxy – Spπ orbital overlap. The crystal structure of SO indicates, that the S-C=C-S and MoS2 planes are approximately coplanar; there are as yet no structural results for reduced SO. At the present there are no structurally defined mono-oxo Mo(VI/V) or Mo(V/IV) mono-ene-1,2-dithiolate models of the active sites available that exist with these oxidation state couples. Such models are necessary to probe the electronic effects of the S---S fold angle which influence Mo dxy – Spπ bonding as the oxidation state of the Mo center changes. However, we will initiate detailed electronic structure studies of the possible effect this fold angle has on reactivity with the structurally defined (L-N3)MoIINO(bdt) complex as a starting point. The axial ligand in the diamagnetic d4 (L-N3)MoIINO(ene-1,2-dithiolate) complexes, has been changed from a strong π-donor (oxo) to a strong π-acceptor (nitrosyl). This axial substitution and the role of the ene-1,2-dithiolate as an electronic buffer to harsh changes in the electron-donating properties of the axial ligand that can occur during catalysis has been reported.51 This axial NO group reverses the energy ordering of the dxy and dxz,yz orbitals observed in the d1 (L-N3)MoVO(bdt) complex such that the dxz,yz orbitals now lie lower in energy than the dxy orbital (π stabilization of dxz,yz) in (L-N3)MoIINO(bdt). This nitrosyl complex is low spin d4, and hence the dxz,yz orbitals are filled as shown in Figure 3b. This is important, as the dxy orbital is now vacant and hence, allows for direct probing of the in-plane Spπ→Mo dxy LMCT transition depicted in Figure 3c. Thus, we have another system for probing Mo dxy – Spπ orbital interactions. The energy and intensity of this CT transition in (L-N3)MoIINO(bdt) will directly probe

38

anticipated differences in Mo dxy – Spπ bonding compared to (L-N3)MoVO(bdt). Resonance Raman spectroscopy has been successfully used to probe the electronic structure of (L-N3)MoIINO(1,2-dithiolate) complexes.64 We will use rR to track the enhancement patterns of the Mo-nitrosyl and Mo-S stretching modes in order to assign the CT bands. The reduction potentials derived from electrochemical studies on (L-N3)MoIINO(tdt)61 indicate that it may be possible to generate and isolate the one-electron reduced [(L-N3)MoINO(bdt)]- species using cobaltocene as a one-electron reducing agent. Our goal is to isolate and structurally characterize this reduced d5 species which contains a single unpaired electron in the dxy redox orbital. Spectroscopic studies using electronic absorption, MCD, and rR will be employed. These studies on the one-electron reduced species will be directed towards understanding the key electronic factors which affect Mo dxy-Spπ orbital overlap, as monitored by the Spπ→Mo dxy LMCT transition energy and intensity. The intensity of this transition has been shown to be an extremely sensitive probe of specific orbital contributions to Mo-S covalency.22,23 These excited state spectroscopic probes of the Mo dxy – Spπ orbital overlap provide a complimentary approach to understanding covalent contributions to the g-tensor anisotropy and the magnitude and anisotropy of the Mo hyperfine coupling tensor. It is with great anticipation that the structure of the one-electron reduced species can be resolved so that the d4/ d5 Mo-nitrosyl ene-1,2-dithiolate complexes proposed here will also serve as first generation electronic models of the d0 Mo(VI) oxidized and d1 Mo(V) reduced active sites by virtue of the number of electrons occupying the dxy redox orbital. Finally, these studies should provide an entry to investigation of the possible role of the S---S fold angle on reactivity. We will also initiate similar studies on the (L-N3)MoIINO(qdt) and the one-electron reduced [(L-N3)MoINO(qdt)]- complex when this system is isolated and structurally

characterized.

a). The S---S fold angle (δ) described before is shown for clarity. b). The splitting diagram for the metal t2g orbitals as a function of axial group substitution is shown and illustrates their relative energy ordering (not absolute energies). c). The three-center pseudo-σ bonding interaction described for (L-N3) MoVO(bdt) that gives rise to the in-plane Spπ→Mo dxy CT transition to be probed.

Note: Clearly, the initial structural and subsequent electronic studies have motivated myself and others to further probe this effect as has been done in several subsequent papers (see Tp*MoObdtCl2 paper where 1st discussed and implied to be further explained in subsequent papers: APES/DFT paper on MoObis(S-S) anions provided evidence that folding was electronic in origin at least for these systems; and the neccesity of considering this distortion in dft calcs to map out MO levels consistent with PES results suggested observed distortion in solid state XRD persisted in the gas phase. Tp*MoOqdt was written a while back that discussed this but was not published untill later. the Tp*MoNO(S-S) paper combined the implications of these oxo-Mo papers and structural results of the MoNO (S-S)complexes and those of the oxo/NO Mo(SPh)2 complexes/ with MO calcs (in particular w/r to these bisthiolates reported, the electronic effect of axial pi acceptor/d4 e- occupation on bonding and resulting electronic structure in the NO systems due to

Mo

E

S

S C

C ψxya'

ψipa'

ϕxya'

ϕipa'

S-Moxy3-center

pseudo-σ antibonding

S-Moxy3-center

pseudo-σ bonding

δ

xz,yz

xz,yz

xyxy

t2g

[MoO]3+ [MoNO]3+

E = O, NO

a)

b) c)

39

M-S interaction/overlap considerations with filled HOMO/empty LUMO, and how this axial LF and resulting electronic structure/e- config correllated to M(NO)-S bonding and subsequent geometric distortions as a function of e- occupation of the HOMO/LUMO; i.e. S orbitals rotate(dihedral optimized) to minimize filled-filled interactions with dxzyz4 was now similarily applied w/r t to dithiolates with restricted rotation) i.e. folding is the way , only way (combined with E-M-S distortions) that dithiolates obtain similar stabilizing/destabilizing interactions with M that influence the nature of those resulting orbitals involved in the redox processes; previously King and also Mcleverty had recognized that restricted rotation of S orbs in dithiolenes prevented such bonding/overlap considerations w/r to e- occupation, but neglected folding for dithiolenes (no XRD yet?)as an alternative way to achieve the same results as free rotation ability in bis thiolates allows; this minimizing principle w/r to interactions with filled vs unfilled M orbitals 1st suggested in the bis thiolate studies was simmilarly applied to dithiolenes by considering folding effects. Folding was further probed by initiating similar studies on Cp-M-(S-S) systems using the dithiolate ligands studied in the Tp* systems. Note that this effect has been observed and described in other systems such as tris(S-S)M and Cp TM(S-S) type systems previously. However, it had not been correllated w/r to electronic structure and reactivity in enzyme active site. My purpose and direction after my dissertation was to probe the geometric properties 1st in a series of new and well characterized Tp*ME(S-S) dithiolates as a function of S-S donor properties and type, metal effects and axial substitution; and correllate these (in particular w/r to folding distortions) to the electronic structure/electrochemical properties of these systems using a variety of spectroscopic techniques including EA/MCD/EPR/RR and PES combined with DFT calcs which could be done in the JHE group (the latter 2 techniques as a probe being a primary reason for joining JHE as well as being able to still collaborate with MLK and his equipment tofurther understand such effects of this distortion and its relation to enzyme structure/function relationships). These implications were to be developed and rigorously probed in subsequent papers using these diff systems. However, a PNAS paper was put forth instead rather suddenly, using this data with previous postulates and ideas developed, prior to the more detailed papers as was envisioned initially to be put forth sequentially and systematically in order to followup previous papers reported and thus define rigorously this distortion and contributions to enzyme in greater detail. Hopefully, this does not detract from the original purpose and numerous papers in progress that were to be submitted eventually after considerable work and effort. Below are some important points reported w/r to the dithiolate fold angle in our systems. Exerpt from Tp*MoO(bdtCl2) paper: In summary, the crystallographic structures for three different (Tp*)MoO(S-S) systems, (1, 3, 4) show that peripheral substituents on the ene-1,2-dithiolate chelate induce no significant structural changes of the inner coordination sphere of the molybdenum center. These results are consistent with other studies of Mo-ene-1,2-dithiolates obtained by X-ray and EXAFS that show little differences in Mo-S distance with changes of the substituents on the ene-1,2-dithiolate.45 However, the substantial difference in the fold angle (θ) of the ene-dithiolate chelate ring between (Tp*)MoO(bdtCl2) and (Tp*)MoO(bdt), warrants further investigation. The structures of 1 and 3 suggest that this geometric feature may be related to subtle differences in the overall electronic structure of the (Tp*)MoO(S-S) systems. It is possible that this fold angle may play an important regulatory role in the reactivity of pyranopterin Mo enzymes during catalytic turnover. DFT calculations are in progress to determine the effects of this fold angle on electronic structure in these well characterized (Tp*)MoO(S-S) compounds.44 Variations in θ may modulate the electronic structure of these systems and could play an important regulatory role in the pyranopterin Mo enzymes during catalysis. The solution redox potentials and the gas-phase ionization energies clearly demonstrate the sensitivity of the (Tp*)MoO(S-S) system to remote ligand effects. However, IR, EPR, and electronic absorption spectroscopies suggest that the electronic structure of 1 and 3 remain relatively unperturbed by peripheral ligation to the ene-1,2-dithiolate. Solvation effects, reorganizational energy changes, and covalent reduction of the effective nuclear charge of the Mo ion due to charge transfer differences involving higher energy acceptor orbitals are currently being investigated as possible contributions to redox potential differences. The crystal structures now available for compounds 1, 3, and 4 provide a framework for high-level DFT calculations to be initiated and evaluated within the context of existing spectroscopic and electrochemical data.44 Such calculations should provide detailed insight into the geometric and electronic structures of these oxo-Mo monoene-1,2-dithiolate centers and help to define structure/function correlations for the active sites of the pyranopterin Mo enzymes.

40

Exerpts from Tp*MoO(qdt) paper: The first coordination sphere bond lengths and angles in 4 are very similar to the corresponding structural parameters for (Tp*)MoO(bdt) (1) (bdt is 1,2-benzenedithiolate). The relatively small inner-sphere structural variations observed between 1 and 4 strongly suggest that geometric effects are not a major contributor to the significant electronic structural differences reported for these two oxo-Mo(V) mono-ene-1,2-dithiolates. This is consistent with the large differences observed in the reduction potential and first ionization energy between the two molecules, which appear to derive primarily from differences in the effective nuclear charges of their respective sulfur donors. However, a subtle perturbation to Mo-S bonding is implied by the non-planarity of the ene-1,2-dithiolate chelate ring, which is defined by the fold angle (θ). This angular distortion (θ = 29.5° in 4; 21.3° in 1) observed between the MoS2 and S-C=C-S planes may contribute to the electronic structure of these oxo-Mo ene-1,2-dithiolate systems by controlling the extent of Sp – Mo d orbital overlap. In enzymes, θ may be dynamically modulated by the pyranopterin, thereby functioning as a transducer of vibrational energy associated with protein conformational changes directly to the active site via changes in the fold angle. This process could effectively mediate charge redistribution at the active site during the course of atom and electron-transfer processes. The key feature obtained from comparing the molecular parameters of (Tp*)MoO(qdt) (4) and (Tp*)MoO(bdt) (1) is that the coordinate geometries are very similar, suggesting that remote effects resulting from ancillary variations to the ene-1,2-dithiolate chelate do not induce significant structural changes involving the inner coordination about the molybdenum atom. These results are consistent with structures of oxo-Mo-ene-1,2-dithiolates obtained by X-ray and EXAFS that show no appreciable differences in the Mo-S bond distance.38,49-51,64,65 However, as these remote effects involve EXAFS indiscernible changes, their contributions to the overall geometric structure in the protein active sites during catalytic turnover can only be elucidated directly by high-resolution X-ray crystallography as it becomes available. This is important, as the molecular structures of 4, 3 and 1 have revealed that remote ligand effects do induce substantial changes in the second coordination sphere, which is evident by perturbations to the fold (θ) and Mo-S-C angles of the ene-1,2-dithiolate chelate. These outer-sphere structural variations may play an important role in fine tuning the electronic properties of oxomolybdenum dithiolates. Therefore, it remains to be determined whether the electronic structure differences observed between these complexes are due exclusively to the electron donating capabilities of the dithiolate ligand S donor atoms, as suggested by the relatively invariant inner coordination sphere metric parameters, or are also a consequence of second coordination sphere effects resulting in structural variations which affect the orientation of those orbitals involved in Mo-S interactions. The most significant structural perturbation observed within the (Tp*)MoO(S-S) system is the fold angle (θ, Figure 5), which exhibits considerable variation among the (Tp*)ME(S-S) complexes that have been investigated (where M = Mo, W; E = O, NO, S; S-S = tdt, bdt, bdtCl2, and qdt).26,30,87,88 For the (Tp*)MoO(S-S) compounds the fold angle varies between 6.9 – 29.5°. The fold angle of 3 (6.9°) is substantially smaller than that of 1 (21.3°) and 4 (29.5°). We are currently investigating crystal packing and electronic contributions to the fold angle in 1, 3, and 4 to assess the role that the fold angle may play in controlling the electronic structure and reactivity of Mo ene-1,2-dithiolate systems.37,89 Previous electronic studies and available crystal structures on various Mo(V)/ Mo(IV) dithiolene complexes such as [Cp2Mo(S-S)]+,90-93 [MoO(S-S)2]- 49-51 and [Mo(S-S)3]- 94 revealed that the fold angle generally decreased upon reduction of the Mo center. This distortion appears to be electronic in origin. In a recent anionic photoelectron spectroscopic and computational study of [MoO(bdt)2]- and related compounds we proposed that the fold angle was electronic and appears to persist in the gas phase.95 We believe that the observed variances in fold angle as a function of the metal, axial substitution, and electron donor properties of the dithiolate ligand in (Tp*)MoO(dithiolate) compounds are also electronic in origin. However, the fold angle observed in 1, 3, and 4 does not appear to follow the trends in the electron donor properties of the dithiolate ligand implied by the measured solution reduction potentials. We have proposed that this structural distortion may fine tune the electronic structure and properties of the oxo-Mo(V) dithiolate systems, and also may play a regulatory role in the pyranopterin Mo and W enzymes during catalysis.30,46 The postulated role of this fold angle30 in conjunction with the obtuse O-M-S angles (oxo-gate hypothesis, orbital overlap model)18 would be to control the orientation (overlap) of the ene-1,2-dithiolate S p(π) donor orbitals with the Mo 4dxy redox orbital and concomitantly with the unoccupied metal acceptor orbitals (dxz,yz, dx

2- y2, and dz2). Although it is not clear at the present exactly how this angular distortion affects the

41

electronic structure and contributes to the observed spectroscopic differences, this folding could possibly play a role in modulating redox potentials by controlling the extent of covalent reduction of the Mo effective nuclear charge via Sσ and Sπ charge donation into the unfilled Mo acceptor d-orbitals. We also would predict that as the Mo site is reduced, a decrease in the fold angle should occur consistent with minimizing interactions of Spπ orbitals with the filled dxy redox orbital. We are currently in the process of evaluating these predictions in a combined spectroscopic and computational study of a variety of structurally defined Mo mono-ene-1,2-dithiolates.37,89

This study shows that the significant differences in electronic structure between (Tp*)MoO(qdt) and (Tp*)MoO(bdt) are not due to changes in the coordination geometry at the molybdenum atom, but rather remote effects mediated by the dithiolate ligands. This result is consistent with a recent EXAFS (XAS) study of several related oxo-Mo-bis(dithiolates) that showed that all of the compounds possessed very similar inner coordination sphere properties.64,65 Finally, we emphasize that the fold angle (θ) between the MoS2 and S2C2 planes may provide a means of controlling the electronic structure by defining the orientation of the Sp orbitals with respect to the Mo d-acceptor orbitals. Changes in the orientation of the dithiolate sulfur orbitals during enzymatic catalysis would certainly be expected to affect ET regeneration of the active site and to modulate the metal redox potential. Dynamic variation of θ by pyranopterin movements during catalysis would provide a molecular transducer for converting vibrational energy associated with protein conformational changes directly into changes in the electronic structure of the molybdenum active site. This process could effectively mediate charge redistribution at the active site during the course of atom and electron-transfer processes. Additional spectroscopic and computational studies are in progress in order to evaluate the functional role of the fold angle and its contribution to the electronic structure and bonding within these and related systems.37 Exerpts from APES JACS paper on MoO(bdt)2]- and related complexes: The X-ray crystal structure of (PPh4)[MoO(bdt)2] shows that the anion in this crystal is also distorted from idealized C2v symmetry, as evident by the non-planarity of one of the chelate rings.70 The same effect, where one of the chelate rings is essentially planar and the other ring is folded along the S---S vector forming a dihedral angle of 144° with the MoS2 plane is observed in the crystal structure of (NEt4)[MoO(ethylene-1,2-dithiolate)2].42 The similar structures of these two different [MoO(ene-1,2-dithiolate)2]- anions in the PPh4

+ salt70 and NEt4+ salt42 suggest that the common distortion of these anions

may be electronic in origin. We also performed DFT calculations, employing the crystal coordinates of [MoO(bdt)2]- (Table S3), to provide further insight into the PES features of 5. The HOMO of [MoO(bdt)2]- (Figure 7), obtained from calculations using the crystal structure coordinates, reveals the effect of the distortion from idealized C2v symmetry induced by the non-planarity (folding) of one of the chelate rings. The results show a considerable amount of S 3p(π) character mixed into the 4dx2-

y2 orbital, suggesting that indeed this folding is electronic in origin. Exerpt from Tp*MoNO(S-S) paper: We believe that the fold angle in compounds 1-3 has an electronic origin that may be attributed to the interaction of sulfur lone pairs (Spz orbitals) with the metal d-orbitals. The folding of the ene-1,2-dithiolate minimizes the interaction of the filled Spz orbitals with the filled metal dxz and dyz orbitals and favors the bonding interaction between the Spz orbitals and the empty metal dxy orbital (Figure 2B). It has been observed that the electronic occupation of dxy orbital has significant effect on the fold angle. The complexes with (dxy)0 electronic configuration have the most folded ene-1,2-dithiolate (1-3: = 41.1 to 44.4) in related group VI complexes. We postulate that the fold angle should significantly decrease as the complexes 1-3 are reduced to (dxy)1 and the ene-dithiolate should become close to planar ( 0) on further reduction to (dxy)2. The metallocene-dithiolene complexes show a fold angle () close to 0 in the 18 electron d2 complexes; upon oxidation this angle increases to = 45-50 in the 16 electron d0 complexes [24,25,62,65,66]. The electronic origin of the fold angles in compounds 1-3 and their oxo-analogues is a current active research area in our laboratory [29,37].

42

Abstracts for ACS (New Orleans) 2002 Dithiolate fold angle variations in trispyrazolylborate molybdenum compounds containing axial oxo or nitrosyl ligands John H. Enemark, Hemant K. Joshi, Frank E. Inscore, Julien T. Schirlin, Michael D. Carducci, Anne E. McElhaney, Ish K. Dhawan, Tonja G. Bill, Nadine E Gruhn, and Dennis L. Lichtenberger The EPR parameters of (Tp*)MoVO(dithiolate) compounds are virtually identical for benzenedithiolate (bdt), toluenedithiolate (tdt), 3,6-dichloro-1,2-benezenedithiolate (bdtCl2) and quinoxaline-2,3-dithiolate (qdt). However, the formal Mo(VI/V) and Mo(V/IV) reduction potentials and gas-phase ionization energies are sensitive to the remote substituents on the aromatic ring. Crystal structures show that the fold angle between the MoS2 plane and the S2C2 plane (Figure 1) ranges from 6.9° (bdtCl2) to 29.5° (qdt) for these formally d1 metal centers. In contrast, the fold angles for (Tp*)Mo(NO)(dithiolate) compounds are larger (41.1-44.4°) and show a much smaller range. The larger fold angles for the (Tp*)Mo(NO)(dithiolate) compounds are ascribed to interaction of the filled symmetric π-orbital of the coordinated sulfur atoms with the in-plane metal orbital that is empty in these {MoNO}4 systems. The analogy between dithiolate folding and linear and bent nitrosyl ligands will be discussed. Metallacycle Folding in Metal-Dithiolate Compounds: Implications for Molybdenum and Tungsten Enzymes Hemant K. Joshi, J. Jon A. Cooney, Frank E. Inscore, Nadine E. Gruhn, Dennis L. Lichtenberger, and John H. Enemark, Gas-phase photoelectron spectroscopy and density functional theory have been utilized to investigate the interactions between the sulfur -orbitals of arene dithiolates and high-valent transition metals as minimum molecular models of the active site features of pyranopterin Mo/W enzymes. The compounds (Tp*)MoO(S-S), Cp2M(S-S) (M=Mo and Ti) (where Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate, (S-S) is 1,2-benzenedithiolate (bdt) or 3,6-dichlorobenzene-1,2-dithiolate and Cp is 5-cyclopentadienyl) provide access to formally d1, d2 and d0 electronic configurations of the metal. Figure 1 shows the metal and sulfur based ionizations in photoelectron spectra of Cp2Mo(bdt). A "dithiolate-folding-effect" involving an interaction of the metal in-plane and sulfur- orbitals is proposed to account for the buffering of electron density at the metal center by dithiolates, and to be a factor in the electron transfer reactions that regenerate the active sites of molybdenum and tungsten enzymes. Some of the work presented in this abstract incorporating data (w/r to Tp*Mo and Cp2Mo and ideas/analysis) was originally obtained for a purpose, specifically 2 papers envisioned, that Hemant and I together were developing and had been working on for over a year, was also submitted previously to PNAS, Joshi, Cooney, Inscore,Gruhn, Lichtenberger, and Enemark. Specifically, I had synthesized Tp*MoO(bdt) to get PES and compare to bdtCl2 in ICA, where we had not shown Gaussian resolved spectra or implications as we were to do this in a 2nd paper with DFT calcs on all related complexes. Also, I wanted to use the bdt PES and calcs to compare to W analog in a paper. The Cp2Mobdt was to be a benchmark in a new paper, and this was reason we had synth with great difficulty, to get new XRD, and neverbefore reported DFT calcs, PES to understand and compare as function of S-S and metal (W). A second batch of Cp2Mobdt synthesized to obtain HeII was used to get closeups of HeI/II and included in this paper. The analysis and understanding of these sytems were already in the advanced stages and consistent with the literature, and although initially were not believed, others soon came around and heralded these ideas. I hope these 2 papers will still be pursued, as it is exciting research. Note: The previous Tp*MoO(bdtCl2) paper tabulated the known XRD/IR/EPR/EA/PES/redox properties of the dithiolene compounds of this system type (oxo-Mo(V) monodithiolenes) collected in the group(FEI/HKJ/AM)/ with the exception of the qdt complex w/r to CV reduction potential (that was ref kirk), but in the recent qdt structure/raman paper we reported our on redox potentials of qdt aquired under identical exp conditions in DCE as the rest of our dithiolene complexes were measured. It should be noted that it was here in the bdtCl2 paper that CV in DCE was first to report rev oxidation pots for such dithiolenes in this system (none observed in MeCN). oxo Mo/W showed this, with the exception of Moqdt where no ox pot here in DCE or in MeCN. Of course the ox pot for NO system are irrev. For all of these systems the reduction pot is rev and attributed to metal based orbital. In M(V) systems both ox and

43

reduction occur in Homo, in Mo(II)NO Ox in HOMO/reduction in LUMO. The CV database of Tp*ME(S-S) complexes under identical conditions allowing for direct comparison and evaluation of trends was further completed in the following paper with M=Mo, E=O, S-S = tdt,bdt,bdtCl2; W; E=O, S-S = tdt; M=Mo, E=NO; S-S=tdt, bdt, bdtCl2which was primarily focused on heterogenous ET rates that did not change for these dithiolenes. It was here that the syntheses of the neverbefore reported Tp*WOtdt and Tp*MoNO(bdt/bdtcl2) complexes were first ref/credited to the appropriate authors, but not explicitly described. The new complex Tp*MoO(edt) remains to be similarly characterized and compared to other available related dithiolenes as was done in the Tp*MoO(bdtCl2/qdt) papers above. Electron Transfer Studies of Dithiolate Complexes: Effects of Ligand Variation and Metal Substitution Anne E. McElhaney, Frank E. Inscore, Julien T. Schirlin, and John H. Enemark* Reactions and operations required for preparing the compounds were performed under strict anaerobic conditions obtained by blanketing synthetic manipulations with pre-purified argon gas and by utilizing standard Schlenk techniques, a high-vacuum/gas double line manifold, and an inert atmospheric glove bag. Glassware was oven-dried at 150C and repeatedly flushed with inert gas prior to use. The employed organic solvents were purified following standard procedures, distilled under nitrogen gas, degassed by freeze-thaw-pump cycles, and transferred to reaction vessels under inert gas via steel cannulae techniques. Reagents used in synthetic procedures were generally used as received. The following reagents (Aldrich) were dried and/or distilled in vacuo and stored under nitrogen gas prior to use: H2bdt (1,2-benzenedithiol), H2tdt (3,4-toluenedithiol), and H2bdtCl2 (3,6-dichloro-1,2-benzenedithiol). Potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate (KTp*)26 and the precursor complexes (Tp*)MoVOCl2,26 (Tp*)MoII(NO)I2,27 and (Tp*)WVOI2

16, 28 were prepared according to the literature. The compounds (Tp*)MoVO(bdt),29, 30 (Tp*)MoVO(tdt),26 and (Tp*)MoVO(bdtCl2)15 were synthesized as previously described. A modified procedure was employed for the preparation of (Tp*)MoII(NO)(tdt)31 and, subsequently, (Tp*)MoII(NO)(bdt) and (Tp*)MoII(NO)(bdtCl2).32, 33 The synthesis, isolation, purification, and characterization of (Tp*)WVO(tdt) involved procedures developed by Young and co-workers.16, 28 Reaction progress was monitored and product purity was confirmed by thin-layer chromatography (silica gel 60 F254 plastic sheets, EM Science). All of the dithiolate compounds were purified under argon by column chromatography (silica gel, 230-400 mesh) prior to spectroscopic and electrochemical characterization as previously discussed in the literature.15, 16, 26, 28, 33 Multiple physical methods were utilized in the characterization of the compounds. Electronic absorption spectra of samples solvated in 1,2-dichloroethane were collected on a modified Cary 14 (with OLIS interface, 250-2600 nm) spectrophotometer. Infrared (IR) spectra (4000-400 cm-1) were acquired in KBr disks or as dichloromethane solutions (between NaCl plates) on a Nicolet Avatar ESP 360 FT-IR spectrophotometer. Mass spectra were recorded on a JEOL HX110 high-resolution sector instrument utilizing fast atom bombardment (FAB) ionization in a matrix of 3-nitrobenzyl alcohol (NBA). Electronic paramagnetic resonance (EPR) spectra of fluid solutions (298 K) or of frozen glasses (77 K) in dry degassed toluene were acquired at X-band frequency (~9.1 GHz) with a Bruker ESP 300 spectrometer for those complexes containing a [(Tp*)MVO]2+ (formally d1) center. 1H-NMR spectra of the diamagnetic [(Tp*)MoII(NO)]2+ (formally d4) complexes were measured on a Bruker DRX-500 spectrometer. The results of these spectroscopic studies were consistent with previous data and confirmed the purity of the samples submitted for electrochemical characterization.14-16, 33 Electrochemical procedures Cyclic voltammetry (CV) and chronocoulometry (CC) were conducted at room temperature with a Bioanalytical Systems (BAS) CV-50W potentiostat. BAS supplied software provided scan acquisition control and data analysis capabilities. The 1,2-dichloroethane (DCE) employed for electrochemistry was of anhydrous grade (EM Science, DriSolv) and required no further purification. Electrochemical measurements were performed on degassed DCE sample solutions (0.5-1.0 mM) over the potential range ±1.5 V (vs. Ag/AgCl reference electrode, BAS) at a platinum-disk electrode (1.6 mm diameter, BAS). The platinum-disk electrodes were polished with 0.05 µm alumina (Buehler) and electrochemically cleaned in

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dilute sulfuric acid prior to use. Solutions contained 0.1-0.2 M dried tetra-n-butylammonium tetrafluroborate ([Bu4N][BF4], Aldrich) as the supporting electrolyte, and a platinum-wire auxiliary electrode (BAS) was used. CV scans of electrolyte solutions showed no indication of impurities within the utilized potential range. Ferrocene (Aldrich) was added to each solution upon completion of the experiments, and potentials are reported with respect to the ferrocene/ferrocenium (Fc/Fc+) redox couple. Each experiment was conducted at least twice for reproducibility purposes. Electrochemical experiments were also repeated using a homemade platinum-disk microelectrode (~200 µm diameter) on acetonitrile sample solutions (0.5-1.0 mM) with an EG&G potentiostat (Model 283, Princeton Applied Research). The acetonitrile (Aldrich) was freshly distilled and passed through a column of alumina immediately prior to use. CV was used to determine electrochemical potentials for the reduction (and, in some cases, the oxidation) of each neutral compound. With the initial and final experimental potentials set ±0.3 V of the redox potential, CC was performed over a range of pulse widths from 250 ms to 950 ms (in intervals of 100 ms). The slopes of the resulting Anson plots (charge versus square root of time) were averaged and used to calculate diffusion coefficients upon application of the Cottrell equation.34 The value for the electrode area employed in these calculations (0.022 cm2) was determined using CC data for ferrocene and the known diffusion coefficient of ferrocene in 1,2-DCE.35 For each electron transfer reaction of interest, data from a series of CVs were recorded at scan rates ranging from 0.1 to 2 V/s (in intervals of 0.1 V/s). Using the Nicholson method, the resulting peak-to-peak separations (Ep) at each scan rate were converted to a kinetic parameter () and heterogeneous electron transfer rate constants were calculated.36, 37 The diffusion coefficients described above were included in these rate constant calculations. Syntheses, isolation, purification and characterization of mononuclear monooxo-Mo(V) monoanionic species with 4Cl- or 4S- donor atoms (4SR- thiolate or 2S-S2- dithiolate ligands) that are isolated /stabilized as salts of large bulky monocationic counter-ions ((PPh4)+ ,(AsPh4)+ ,(NEt4)+ ), which minimizes the well known propensity of {MoVO}2+ systems to dimerize in the presence of trace water (there being 2 well known approaches to prevent such dimerization; bulky counterions as employed here or sterically restricted ligands coordinated to metal such as Tp* used in above 6-coord systems; a 3rd method for stabilizing M-S complexes is by using sterically bulky thiolate (dithiolate?) ligands). These include [MoO(CL)4]-;[ MoO(SPh)4]- , [MoO(SPhCl)4]- ; [MoO(EDT)2]-; MoO(bdt)2]- and the new complex [MoO(bdtCl2)2]- isolated as tetraphenylphosphonium salts that were characterized (MS-ESI(MeCN),IR,EA,EPR) and studied by solution(MeCN) anionic PES,and those complexes with XRD reported structures further evaluated by DFT calcs (geo optimized vs crystal coordinates fixed). The unstable species, “[MoO(SPh)2(bdtCl2)]-“ was also isolated and identified (by MS-ESI)from the main reaction route after 2 hrs to the target complex [MoO(bdtCl2)2]-. However, this intermediate was not further pursued as Dick Holm has already reported similar mixed species using a different method directed (successfully) towards preparing Mo(VI) dioxo and Mo(V) monooxo monodithiolene models of sulfite oxidase. The presence of this intermediate after similar reaction time/ at RT w/r to the bdt and EDT complexes suggest incomplete conversion for this particular target, and thus must consider reacting for longer time and/or at a higher temperature for full consumption of H2(bdtCl2) ligand and complete ligand exchange (conversion) to target. This complex exhibits similar properties with the bdt analog, both possessing 2 dithiolene ligands relevant to DMSO reductase family of Mo enzymes that are believed to be retained throughout the catalytic cycle (Mo cycles during turnover through +6/5/4 oxidation states following formal OAT, which exp shown as proper OAT here and results in reduction of substrate DMSO to DMS concommitant with desoxo-Mo(IV) resting state being ox by 2 e- to Mo(VI) in a single step; followed by ET regeneration of the resting state via 2 sequential 1e- transfer processes to the Mo(VI) and resulting Mo(V) sites respectively; i.e. formally 1e- oxidation involving the metal .) Probing the Electronic Structure of [MoOS4]- Centers Using Anionic Photoelectron Spectroscopy Xue-Bin Wang†, Frank E. Inscore‡, Xin Yang†, J. Jon A. Cooney‡, John H. Enemark‡*,Lai-Sheng Wang†* (AsPh4)[MoO(CL)4,(PPh4)[MoO(CL)4] from MoCl5/(PPh4)[MoO(Cl)4H2O] from (PPh4)[MoO(CL)4]+H2O;

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Following reported procedures; and also suggested quick route of Dr.Carduccii and his reported procedures (e.g. Dr. Carduccii route: (PPh4)[MoO(CL)4] from: MoCl5 +DCM(wet)/ heat-stir till turns green then add in 1equivalent/excess of PPh4Cl, then filter and purify according to reported procedure.) MoO(SPh)4]- , MoO(SPhCl)4]- from MoOCl3(THF)2 from MoCl5; Followed standard reported procedures (see above) or with slight modifications. Mod proc. 10 g MoCl5 (dried in vacuo and /or sublimed) was suspended in 50-100ml of degassed CCl4, stirred for 15-20 min to make sure no solid clumps on bottom of flask, and then cooled in dry ice/acetone bath (~-20degC) under Ar, then 50-100ml of THF (dried over Na/benzophenone,freshly distilled under N2) degassed and transferred via steel cannulae to reaction flask (slowly w/r to exothermic reaction). If cooled down enough, and sufficiently solvated, should be able to add all THF without target ppting out. Let warm to RT/initiate exothermic reaction at which the dk brown-black solution upon becoming warm (hot quickly as exothermic) is quickly and anaerobically filtered, and allowed to crystallize from the green solution formed upon filtration , filtered, solid washed with CCl4, and dried in vacuo (~15g of MoOCl3THF2 solid). Can recrystallize at~-20degC. 5g MoOCl3THF2 (0.0138mol) under Ar dissolved in 50 mlMeCN (from P2O5 or drisolv),. In a dropping funnel the HSPh proligand (6.519 ml) and 7.669 ml TEA combined in 50 ml MeCN, which was added dropwise to reaction solution stirring, and filterd after suitable time. Then solution conc where 7.23g of PPh4Br in MeOH (100ml) was added dropwise slowly. The blue crystals formed were filtered and washed with MeOH. MoO(bdt)2]-, MoO(EDT)2]- syntheses have both been reported but with very little detail by direct ligand exchange of the appropriate dithiol (≥2;~2.2 equivalents) with MoO(SPh)4]- in DCM (at RT/rt=?) with subsequent XRD suitable crystals obtained by diffusion of diethylether into solution. Similarily but with more detail provided by Dr. Jon McMaster in England (aquired previously with Enemark group) in private communication with me with slight modifications that added solvents/reagents to the top of a schlenk filter tube under sufficient pos Ar pressure (connected to the reaction flask) that resulted in the solution being maintained ontop of the frit, allowing it to be deoxygenated by the bubbling Ar stream prior to introducing to the reaction flask/mixture; and upon completion of reaction resolvated dried residue of filtered filtrate with fresh DCM under Ar, transferred to a schlenk storage tube and layered with diethyl ether in a 1:4 ratio under Ar to ppt out and obtain relatively pure crystalline material. In addition, a modification of these methods were also developed with consultation with Dr. Nick Rubie (of Kirk research group at UNM where we had previously prepared successfully the bdt complex and precursor) and applied to the preparation of both of these complexes and the new complex as described below and reported in the following study. NOTE: As the bdt complex is somewhat characterized and more stable than the EDT complex (one of the most difficult to isolate and prevent decomposition from green/black to mixture with brown even in schlenk flask as powder), and the bdtCl2 compound represents a new synthesis, we have used the bdt complex as a control to optimize the best method for obtaing these models (3 different reactions tried to test and reproduce the methodologies which are to be used to prepare the EDT and bdtCl2 compounds; the 1st reaction for making the bdt complex followed the reported procedure with modifications employed by Mcmaster, the 2nd employed the new methodolgy tested here and 3rd was to evaluate and reproduce and optimize reaction 2 for further applications). NOTE: The SPh precursor complex is also extremely unstable and difficult to purify (especially in solution) and very sensitive to air, more so than the bdt complex. This is evident by the more rapid decomposition of SPh precursor (deep blue/violet) in solution vs bdt product (green/black) as directly observed by the very fast distinct color change in a capped vial sat with Ar on the bench. The acquisition of EA data for these compounds (especially the precursor) required use of anaerobic cells, and still over time the initial starting solution of SPh precursor would decompose in these cells upon transfering. However, employing rigorous exclusion of oxygen/water conditions and minimal exposure times EA is valuable for monitoring the reaction progress (the general electronic features being well known for both of these 2 species) as the distinct low energy CT band in SPh compound dissappears upon forming the bdt species which exhibits a much lower energy CT band well separated and distinct from this precursor. The absence of this precursor CT band implies conversion is relatively complete. MS(ESI) and EA were the primary tools I employed to follow and identify reaction progress/ purityand identity of products. EPR

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(and IR) has also been employed to monitor reaction progress/product purity /nature and behavior and was also used here. Note that MS(ESI) was used to identify the target in the crude reaction mixture and subsequent isolated/purified product, as well as monitoring the absence/presence of SPh precursor and/or mixed SPh/(S-S) intermediate species in final product was also checked by MS. Each of the primary targets reported and characterized in this PES study were 1st identified by MS(ESI in MeCN). MoO(bdtCl2)2]-, “MoO(SPh)2(bdtCl2)]-“ The new target model synthesized and reported in study below was also synthesized by employing the modified method as presented in the JACS paper. NOTE: The highly purified dried/ oxygen free SPh precursor was checked again for decomposition, dried in vacuo in predried/purged/evacuated reaction flask upon being weighed and transferred in glove bag under Ar to flask, which is also under positive Ar flow being connected to vacuum/inert gas manifold, and sealed with septum. Extremely pure solvent (DCM; Drisolv-EM Science) deoxygenated by Ar bubbling, dried under inert atm by distilling over molecular sieves following running through collumn of molecular sieves under Ar, was saturated with Ar, degassed via several FTP cycles and transferred anaerobically by steel cannula to reaction flask(initially under Ar press with peircing of septum, then evac under vac to provide reduced press for initiating solvent transfer to it) where resulting suspension/solution stirring was purged /evac in vacuo/ sat with Ar for 20 min at RT. ~30 mL DCM per 1g of precursor. The dithiol proligands employed in this study were obtained and purified as follows; The highly purified H2bdt ligand was synthesized from HSPh (freshly distilled under vacuum) and purified by vacuum distillation using the most efficient/highest yield and purity producing procedure reported (nearly clear/white crystalline material obtained under Ar below RT in vac, which was stored in air tight schlenk flask in fridge prior to use (as MP is ~23deg C lowering the temp maintains it in less volatil form the solid being less sensitive to air (oxygen) than as a liquid, decomposition appears to correlate with change in color to a brown more liquidy substance). This synthesized bdt dithiol and commercially obtained EDT dithiol (purged/Ar sat) were purified prior to each reaction, where using a specialized custom distillation set up these ligands were distilled anaerobically in vacuo/collected/transfered under Ar to ensure purity(no water/oxygen/disulfides) before introducing (slowly)by steel cannula (or gas tight syringe) to reaction flask(predried in oven/purged and evacuated with Ar/vacuum; and similarly treated reagents/solvents) employing pos Ar pressure/purging and evacuation in vacuo cycles to maintain rigorous exclusion of air(oxygen/water) prior to,during and following transfer). The bdtCl2 dithiol (a solid off white, at RT) dried in vacuo and purge cycles was obtained commercially (containing ~5% bdt dithiol contaminant). 0.479g (.5g, 0.562 mmol; 889.08 g/mol) (PPh4)[ MoO(SPh)4] in 15mlDCM + Ar sat0.162ml (0.20g, 1.905mmol, 142.24g/mol,1.236g/ml) H2(bdt) in slight excess ~2.2equivalents reacted for 2.5hrs to dkgreen/black 0.496 g (.5g, 0.562 mmol; 889.08 g/mol) (PPh4)[ MoO(SPh)4] in 20ml(15ml)DCM + ~0.11ml Ar sat (0.1038ml, 0.562mmol, 94.20g/mol,1.123g/ml) distilled H2(EDT) in slight excess ~2.2equivalents reacted for 2hrs to dkgreen/black 0.785 g (1.0g, 1.125 mmol; 889.08 g/mol) (PPh4)[ MoO(SPh)4] in 30mlDCM + Ar sat 0.4127g (0.5224g, 0.2474mmol, 211.13g/mol) H2(bdtCl2) in slight excess ~2.2equivalents reacted for 4.5hrs to dkgreen/black The stirring reaction mixture, upon dithiol ligand (liquid dried/purified by vacuum distillation,sat with Ar and purged several times; or solid dried in vacuo with slight heat and purged several cycles by Ar sat/vacuum) being transferred anaerobically to the reaction flask (precursor/precursor-solvent suspension/solution) was purged quickly by several cycles of flushing with Ar and evacuation, then allowed to stir/react at RT under a Ar blanket, maintained at a pos press for 2hr/(5)with H2bdt/(H2bdtCl2). Under Ar, schlenk flask connected to frit tube was connected to reaction flask under Ar, the bottom vaced , and react flask turned upright to filter solution/ salt collected. Filtrate in flask connected to schlenk flask

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containing 75ml Et2O with frit tube both under Ar, sideways, then vac on filtrate flask turned upright put filtrate on top of frit with Ar bubbling through, and ether vapor pulled through solution as shown in figure. The stream of Ar eventually caused these targets to crash out. A vac was pulled on bottom to remove solvent. Then washed with cold Et2O, and then cold MeOH was used to wash the powder (remove excess ligand), followed by drying in vacuo.

Compound Amount needed mmol FW mp (C) bp (C) density (g/ml) (PPh)4[MoO(SPh)4] 0.5 g 0.562 889.08 ethane dithiol (H2EDT) 0.1 ml 0.562 92.40 144-146 1.123 dichloromethane 20ml diethyl ether All solvents were anhydrous (Drisolv) and degassed by freeze-thaw-pump method and ethane dithiol (Aldrich; 90%) was purified by vacuum distillation /under Ar prior to use, and the collected material in a schlenk flask was purged several cycles by a combination of Ar saturation and subsequent slight vacuum. In a prepurged glove bag, under a positive pressure of dry Ar (pure Ar passed through a collumn of activated drierite prior to entry into bag), (PPh4)[MoO(SPh4)] (0.5g, 0.562mmol) was weighed and placed in a 100ml schlenk flask along with a stirbar, then capped with a septum and purged several cycles, the dried under vacuum for several hours. After purging several times with argon and vacuum, 20 ml of previously degassed (via FPT) dichloromethane was transferred anaerobically to the solid by steel cannula and the mixture was stirred for 2 hours at room temperature. During this time, the color of the solution slowly changed from dark green to virtually black. The solution was filtered anaerobically, that resulted in a (gold-yellow or light blue?) salt collected on the frit. Purification: The first attempt to purify the product was done by slow vapor diffusion: Under a positive pressure of Ar gas, the schlenk flask containing the filtered product was attached to a coarse-frit filter stick and then connected to another 100 ml schlenk flask containing approximately 75ml of cold diethyl ether. A significant flow of Argon (~20 psi) was run through the schlenk flask containing diethyl ether while a slight vacuum was pulled on the side containing (PPh4)[MoO(edt)2]. Next, the apparatus was turned upright allowing diethyl ether vapors to diffuse through the solution of (PPh4)[MoO(edt)2] which should stayed above the schlenk frit. See Below: Unfortunatly this method was not very effective as (PPh4)[MoO(edt)2] crashed out as an oil on the frit. Several attempts using this

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method were tried by resolvating oil with DCM on frit, but still did not crash out as a powder similar to above reactions, which were succesful with the bdt type ligands. The second attempt to purify the product was done using mixed solvents: The (PPh4)[MoO(edt)2] oil was again solvated in sat DCM solution which was added to cold, dry, degassed diethyl ether (1:4) and the product crashed out immediately, and then again appeared to form an oil.

NOTE:It was at this time that I took Pablo under my guidance and introduced him to Schlenk techniques and proper methodologies employed in reactions requiring total exclusion of air(oxygen/water). This was his first experience with these complicated but necessary procedures. His initial understanding of inorganic reactions such as these (very limited but motivated), where success begins by knowing how to control the initial 3 exp components (the precursor, proligand, and reagents/solvents) based on their behavior under a given set of conditions, was introduced to him here and reiterated, as I proceeded through this set of exps already in progress. This introduction/tutoring w/r to choice of very complicated synthetic procedures is significant as it provided him with confidence and the ability/tools to approach and solve various synthetic problems (in particular future independent research) employing a solid foundation of aquired techniques and exposure to proper synthetic methods applicable to very complicated systems as well as those much simpler. Such insight is gained either by long term trial and error and may still be limited or by the guidance of one who is considerably experienced in such matters. This way quickly and properly couples one into a more active and participating role w/r to the research program, its goals and success/contributions. Regarding these applications and components, I first had Pablo set up the purification by anaerobic distillation under vacuum of the already prepurified/synthesized bdt dithiol ligand for practice followed by the more difficult commercially obtained EDT dithiol necessary for the success of this synthesis. Although not involved in the initial preparation/purification of precursors (MoOCl3THF2/[MoO(SPh)4]-) solvents and other reagents; experience was obtained with exposure to how reactions are setup and thought through in all aspects, solvent and reactant prep, and methods/manipulations and techniques for rigorous exclusion of air(oxygen/water) from reaction and maintaining such conditions during isolation and purification steps. I.e. this involvement showed him how all aspects of a synthesis can be controlled/tested/maintained with the proper knowledge of certain methodologies and technique applications. His understanding of schlenk techniques aquired initially by observations from the last bdt complex synthesis and tested by his more direct involvement permitted and encouraged w/r to the EDT complex preparation has provided him with the tools that he now employs successfully in present research (semi-independently). This is evident by his clear grasp of the mechanical aspects of the reaction procedures and subsequent understanding/contributions for optimizing methodologies. His assistance provided in the synthesis of the EDT complex (as he observed initially

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from the bdt prep) was encouraged as an introduction and his eagerness and ability to learn and apply these techniques warrants this reaction system to be included in his theses; a great learning experience for him. Synthesis. All reactions and synthetic operations, unless noted otherwise, were performed under a dry inert atmosphere of pre-purified argon using Schlenk techniques, a double line high-vacuum/gas manifold, and a polyethylene glove bag. All glassware and accessories were heated, purged with argon, and when possible evacuated prior to use. THF was dried and purified by distillation over Na/benzophenone. All other solvents (CCl4, CH3CN, CH2Cl2, MeOH, Et2O) were used as received (Drisolv; EM Science). These solvents were thoroughly degassed by repeated freeze-pump-thaw cycles, and transferred to reaction vessels via steel cannulae techniques under a positive pressure of dry argon. The reagents (Aldrich), MoCl5, tetraphenyl phosphonium and tetraphenyl arsonium chloride salts, were dried in vacuo prior to use. The ligands (Aldrich), HSPh (thiophenol), HSPhCl (4-chloro-thiophenol), H2EDT (1,2-ethanedithiol), and H2bdtCl2 (3,6-dichloro-1,2-benzenedithiol), were distilled and/or dried in vacuo prior to use. H2bdt (1,2-benzenedithiol) was synthesized according to literature precedent,65 and purified by vacuum distillation. The [PPh4]+ salts of [MoOCl4]- (1), [MoO(SPh)4]- (2), and [MoO(SPhCl)4]- (3) were prepared according to published methods.66-68 The syntheses of the [PPh4]+ salts of [MoO(EDT)2]- (4) and [MoO(bdt)2]- (5) have been previously described.69,70 A modification to this procedure was used here to synthesize and purify the [PPh4]+ salt of theseand the new complex, [MoO(bdtCl2)2]- (6). To an evacuated flask containing a mixture of precursor 2 suspended in CH2Cl2 (23°C) was added two equivalents of the H2bdtCl2 proligand, which was stirred under argon for 4.5 hours, then filtered anaerobically. The resulting solution was then transferred onto a coarse glass frit (filter tube) connected to a flask containing Et2O. A positive pressure of argon through the solvent flask provided a slow diffusion of Et2O vapor into the solution maintained on top of the frit (via slight vacuum pulled through top flask to maintain press differential and subsequent constant Ar flow). The slow stream of Et2O forced through this saturated solution eventually effected a dark black/green material to precipitate out, which was subsequently collected by filtration, washed with Et2O, followed by cold MeOH to remove any unreacted dithiol. The powder collected was dissolved in a minimum amount of CH2Cl2 and layered with Et2O in a 1:4 ratio. Green-black crystals of 6 were filtered and washed with Et2O. The oxo-Mo(V) complexes were characterized by HR-ESI(±) in CH3CN. The (PPh4)[MoOS4] compounds investigated in this study are air sensitive, especially in solution. Hence, the preparation and manipulation of these samples required the rigorous exclusion of both oxygen and water. Samples were stored in a dry inert atmospheric glove-box until needed. Photodetachment photoelectron spectroscopy. Details of the ESI-PES apparatus were published elsewhere.58 Only a brief description of the experimental procedure is given here. To produce the desired anions, we used 10-3 M solutions of the [PPh4]+ salts of 1-6, respectively, in a pure and oxygen-free CH3CN solvent. The solutions were sprayed through a 0.01 mm diameter syringe needle biased at –2.2 kV in a nitrogen atmosphere. Negatively charged ions emerging from a desolvation capillary were guided by a radio frequency-only quadrupole ion-guide into an ion trap, where the ions were accumulated for 0.1 second before being pushed into the extraction zone of a time-of-flight mass spectrometer. The main anion signals corresponded to the anionic species of each compound. The anions of interest were mass-selected and decelerated before being intercepted by a laser beam in the detachment zone of the magnetic-bottle PES analyzer. For the current study, 266 nm (4.661 eV) photons from a Q-switched Nd:YAG laser, and 193 nm (6.424 eV) and 157 nm (7.866 eV) photons from an excimer laser were used for photodetachment. Photoelectrons were collected at nearly 100% efficiency by the magnetic-bottle and analyzed in a 4 meter long time-of-flight tube. Photoelectron time-of-flight spectra were collected and then converted to kinetic energy spectra, calibrated by the known spectra of I- and O-. The binding energy spectra were obtained by subtracting the kinetic energy spectra from the corresponding photon energies. The energy resolution was about 10 meV (FWHM) for ~0.5 eV electrons, as measured from the spectrum of I- at 355 nm.

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Tp*MoO2SPh prepared as reported (XRD reported in DCM/MeOH) Tp*MoO2Br (0.5 g, mwt = 505.034g/mol 9.9003 x10-4 mol; ~1mmol) was placed in a 100 ml round bottom schlenk flask w/ stir bar, and dried in vacuo. 30 mL of anhydrous/degassed DCE (Drisolv) was transferred to the reaction container by steel cannula, and the yellow suspension was stirred under an atmosphere of Argon for 20 min/ and purged a couple of times. A mixture of HSPh (0.22 ml), Et3N (0.55ml, mmol) and toluene (2ml, dry, degassed) was added and the reaction was stirred for 2 hours at room temperature. After about 10 minutes the solution turned from bright yellow to dark brown. The resulting solution was filtered, concentrated down and chromatographed on silicagel using DCE as eluent, collecting the first dk brown band. See my rR(benz/solid) and EA(DCE) data obtained. I want to redo both exps as I think the sample still had contaminants as I was in a hurry to get to NM the next morning. Need to send Nick some fresh very pure sample as soon as Pablo has some. Tp*MoO2SCH2Ph; I used a method similar to above as suggested by McMaster when he visited our lab but prepurifying the precursor before the reaction, and using 2 collumns to purify the target. Prepurified/dried Tp*MoO2Br (250mg, 0.495 mmol) was placed in a 50 ml round bottom schlenk flask w/ stir bar, and dried in vacuo and purged several times. 10 mL of dry/degassed DCM (Drisolv) was transferred to the reaction container by steel cannula, and the yellow suspension was stirred under an atmosphere of Argon for 10 min/ and purged a couple of times. A prepurged mixture of HSCH2Ph (1.1 eq) and Et3 N(1.2 eq) in toluene (5ml, dried and distilled over Na/ Benzophenone/degassed ) was added anaerobically, and the reaction after purging a couple of times was stirred for 2 hours at room temperature. The resulting solution (under strict anaerobic and dry conditions) was filtered, concentrated down, refiltered and immediately chromatographed (flash chromatography under Ar) on silicagel (200-430 mesh, prepared in schlenk flask, stationary phase dried by heating in oven then placing frit on flask and evacuating in antechamber of glove box for 1hr, then in glove box sealed with septa, then transferred to glovebag under Ar where dry/degassed DCM was transferred to it and stirred with Ar sat) using dry degassed DCM as eluent in a short collumn. The orange brown fraction was collected in a schlenk flask where it was purged several times. A 2nd short collumn and several extractions/washings/ppting out and filtrations was also ran on this fraction. The

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sample of the final dried in vacuo orange material was then submitted for recrystallization. Pablo has the rest of my original material. Some of the sample I had sent down to Nick Rubie for rR studies at UNM. XRD(liquid diffusion of dry/degassed MeOH in sat DCM solution), Note the more dry (degassed) solvents better as when it sets in this mixture for more than 2 days see white material ppt out indicating decomposition. It took me several attempts to get suitable crystals for XRD. They were very small and I almost gave up, finally succeeded, Mike Carduccii says this compound has some of the most difficult crystals he had ever worked with. I believe Hemant did the final refinement on this crystal. RR(Nick Rubie, solid and benz) and EA(DCE on Olis) data obtained. Goal to compare to that for SPh analog w/r to understanding torsional angle effects/ SR bonding and rR probes related to SO +6 active site. NOTE: This system is now being continued by Pablo as a project for his UG Honors Theses. He has now synthesized ~9 complexes in this system, as well as resynthesizing the 2 above, and including I believe a couple of new complexes. John, Just a brief summary of the Cp2M(S-S) project, where we started ,where it stands today, and why it should continue. As you remember, we started this study as a Chem 412 project that was initially thought to be easy for the students to make. This was not the case, as seen in the inability for Jon’s students to make the V analogs, the difficulty of my student, and the fact that it took all summer 2002 to make the Mo and W series shown below. This was our initial Goals and reasons for study: To synthesize, purify and characterize an isostructural series of heteroleptic high-valent transition metal complexes possessing both cyclopentadienyl and dithiolene ligands. The two classes we are interested in are of the following general formula: 1). Cp2M(dithiolene)0, where in this neutral complex Cp is the prototypical C5H5

- ligand, M is a group 6 metal (Mo, W) in the +4 oxidation state, i.e. d2 M(IV), and dithiolene is the dianion bdt (benzene 1,2-dithiolate i.e.-S-(C6H4)-S - ). These systems can be characterized by UV/Vis, IR, NMR (since diamagnetic), HR-MS, and of particular interest and promise: gas-phase PES, being applicable as these are neutral species and significant as this technique has not previously been used to probe the electronic structure of this system. GP-PES has been applied previously to structurally/electrochemically/ and spectroscopically well characterized Mo/W d1 Tp*MV O(dithiolene) complexes to further probe M-S covalency and geometric/electronic relationships as a function of the e-donating capabilities of the dithiolate (remote ligand effects), the metal (and axial substitution effects with d1 Mo(V)S; d4 Mo(II)NO analogs). However,the Tp* ionizations overlap with the majority of S based ionizations and this precludes much insight into M-S interactions, and is further complicated by the extremely covalent bonding observed within this particular system, and leads to the question as to what is the true nature of the tentative assigned 2 Sop bands (not well resolved) and the M based band (HOMO?) at lowest BE that overlaps to an extent with these at higher energy, and also the origin of energetic shifts with changing S donor properties. Cp ionizations are known to occur at much higher binding energy, and thus for this system, GP-PES may

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provide additional insight regarding M-S bonding here due to a potentially greater energetic region free from other interfering ligand ionizations of little interest. This system provides another series of Mo(IV/V)-monodithiolene complexes relevant as possessing the minimal/common structural feature in pyranopterin Mo enzymes, in particular SO (note there are no other reported Mo(IV)(monodithiolene) complexes except those of this system type, and if we can generate the d1 Mo(V) cation analog, this will allow a very significant comparison w/r to changes upon e- occupation between isostructural analogs that has yet to be achieved in the more relevant oxo containing monodithiolene systems). 2). CpM(dithiolene)2

-1,0, where now we have one Cp ligand and 2 dithiolenes (ie bis-dithiolene) coordinated to the Mo and W cations. However, this system unlike the above 18e- neutral system, is initially isolated as a 16e- monoanion, but with the the metal still as formally d2 M(IV). One interesting feature of this system is that we can now oxidize the monoanion d2 M(IV) to a neutral paramagnetic 15e- d1 M(V) system. The different oxidation states require different spectroscopic techniques to characterize them. e.g. these d1 paramagnetic complexes are amenable to EPR and MCD spectroscopy and in addition by being neutral can be probed by gas-phase PES (a first for applying these techniques to such a system; there is some EPR data on related systems). Furthermore, the monoanionic parent species can be probed by a new technique known as anionic PES. The gas-phase results of these neutral Mo(V) bisdithiolates can then be compared to the monoanionic oxo-Mo(V) bisdithiolate analogs previously probed by APES. How does the electronic structure change upon removing the terminal oxo? This is important as the DMSOR Mo(IV/V) bis(dithiolene) active sites are desoxo (O-M) not terminal oxo (O=M), and although there are reasonable M(IV) desoxo models available, none exist for Mo(V) oxidation state, and little is known about the electronic structure of such desoxo systems, and therefor the effects of e- occupation between isostructural M(IV)/M(V) analogs as related to ET regeneration of the M center in enzyme active site. d1 Mo(V) systems being paramagnetic are amenable to study by additional techniques such as EPR and MCD, which has also been primarily the only spectroscopic techniques employed for the majority of the enzymes due to other interfering prosthetic groups; but as these 2 methods are sensitive to paramagnetic centers only (the prosthetic groups being diamagnetic, and even with heterogenous samples containing diamagnetic +6/+4 species) these are powerful (w/r to info content)/ highly –sensitive (only minute quantities) and selective (paramagnetic specific) tools. Considering these facts, the formally d2 CpMo IV(S-S)2]- / d1 CpMo V(S-S)2] isostructural analogs are at least at this point, a reasonable system to probe the electronic structures of Mo(IV/V) bis(dithiolenes) in the absence of a terminal oxo. More importantly the application of GP-PES to the Mo(V) neutral complex provides additional insight, that when combined with XRD,CV,rR,EA and DFT calcs will be extremely effective. A direct comparison of these results to the similarly characterized oxo-Mo(IV/V) bis(dithiolene) system with dithiolate ligand parity, will also be helpful in understanding the desoxo-Mo active sites. Scheme 1. shows the general synthetic route that is required to prepare these complexes. We are very interested in obtaining pure samples of these in order to study M-S bonding interactions via various spectroscopic techniques. The neutral complexes above will be useful for understanding the gas-phase photoelectron spectra of more complicated systems. In addition to d2 Mo(IV) and W(IV), we can also make d1 V(IV) and d0 Ti(IV) analogs. These complexes are of further interest because X-ray crystallography has shown that the folding of the dithiolene along the S-S axis changes dramatically as a function of electron configuration (~0-9 deg for d2, 30-40 deg d1, 40-50 deg for d2). A comparison to isostructural G4/5 metal dithiolene analogs of the same oxidation state but that differ by e- occupation will be helpful in making band assignments in GP-PES as we have previously done for APES studies reported

M

CpM(CO)3Cl

Cl

ClM

S

SNa2bdt+ 2NaCl

2 bdt 2-M

S

S

S

S+Cl- + 3CO

-

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(Mo(V) d1 vs V(V) d0 isostructural analogs allowed definitive assignment of metal based ionization in MoO(bdt)2]-). A particular issue is whether the observed trends/or absence of w/r to electronic/geometric properties observed in the Tp*MO(monodithiolene) system as a function of the e- donor ability of the dithiolate is also observed for the bis-CpMo/W monodithiolene system with analogous ligands, and with those trends reported for the different bis-Cp Ti/Mo/W (IV) monodithiolenes of the DMIT (S rich) type. Fourmigue, M; Coordination Chemistry Reviews, 178-180 (1998) 823-864. Please refer to ref’s 75, 78 ( and 13,19,33,36,38,39,72-74, 83-85) within. This is the study I had originally put together as influenced from the initial data and what was known in the literature acquired prior to,during and immediately after the 412 project. (NOTE: The initial failures/limited availlability and time deadline of the 412 student forced me to come in and try some different methods/ and more rigorous conditions which worked and finally provided Cp2Mo(bdt), the results of which I presented to the student for poster session the next day; still she learned some basic techniques). The point being that this was not an easy synthesis as first thought it would be. These difficulties resulted in myself and Hemant doing a massive/ thorough search of the literature to address certain reactivity difficulties encountered in the initial syntheses. This was very useful as it resulted in the formulation of specific issues and testable hypotheses, making this system far more interesting than previously considered. A significant amount of insight was achieved in summer (2002) by direct and systematic experimentation. Preliminary Study 1. Goal: to elucidate the electronic structure of Cp2Mo(S-S), using bdt as the benchmark compound. Derive an MO scheme that can explain experimental observations. e.g. Folding/ geometric evolution of folding as function of oxidation state/ e- occupation/nature of S-S and its donor properties? Does trend in e- donor properties of S-S follow Fourmigues prediction w/r to folding, or as we observed in Tp*ME(S-S) series? Based on trends/observations reported in literature with DMIT type ligands (and asymmetric quinoxaline types) and from our initial synthetic/characterization results, what do we expect from our system of dithiolene complexes chosen for study: Changes in metrics(M-S,C=C/C-S) as function of oxy state/S-S donor properties? Redox behavior, reversible reduction dependent upon metal(Mo vs W?); 2 rev oxidations, dependent upon nature of S-S?, independent of metal?; ligand based or metal based HOMO/LUMO? EPR showing g values of paramagnetic Mo species but hyperfine(95/97Mo in Gauss) small vs Cl precursor? Reactivity differences, d2 vs. d1/d0? NOTE: See this in Ti vs Mo ligand exchange reactions, the stability/reactivity differences has been attributed to the electronic structure as a function of e- occupation; and further this may be due to electronic effects that may reflect or be due to folding differences as function of e- occupation. What is reason for Cp displacement in our

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system , and does it appear to depend upon nature of dithiolate, the amt of dithiolate proligand, or the conditions employed for ligand exchange? Why is direct synthesis of Cp2Mo(S-S) difficult via H2(S-S)/ Et3N or by Na2(S-S) in organic solvents vs that in G4 (Ti) analogs? -Utilize PES HeI/II (NeI?) as primary exp method to study bonding (Sop-M). Powerful method when combined with DFT calculations and XRD defined structures. No one has used PES to study such systems. -What is the origin of the S-S folding; extent of folding as a function of oxidation state (e- occupation), the metal, and the nature of the ene-dithiolate? I. Syntheses, Physical Characterization and Theoretical Studies of Cp2M(Y,Y) Complexes (Mo,W) A. Cp2M(S-S) 1. Cp2M(bdt) a). Cp2Mo(bdt). 1). determine methodology for synthesis, isolation and purification of complex. 2). characterize by TLC, HR-MS (ESI/FAB), IR (solution/solid-state). 3). solution 1H-NMR (RT(500 MHz)/VT(300 MHz)), and 13C-NMR(RT). 4). determine solution electrochemical behavior (CV). 5). probe electronic properties: solution/solid-state electronic absorption. 6). probe electronic properties: gas-phase PES (HeI/HeII/(NeI)) 7).determine geometric structure single-crystal XRD. 8).from culmination of studies: optimize synthesis/isolation/purification steps, characterize chemical properties (solubility/stability), identify side products. 9). computational studies (ADF-DFT) of neutral d2 Mo(IV) complex. 10).Additional spectroscopy: solution/solid-state resonance Raman spectrum/ Mo-S profiles?. b). Cp2W(bdt). similar studies of W analog. 2. Parallel studies on Cp2M(benzene dithiolate ring derivatives). a). Primary bdt ring derivatives: Cp2Mo(bdtCl2) and Cp2Mo(tdt). b). Cp2W(bdtCl2) 3. Parallel studies on Cp2Mo(qdt). 4. Parallel studies on Cp2Mo(edt). B. Other Cp2M(Y,Y) complexes. 1.Cp2MoCl2 /Cp2WCl2 2.Cp2Mo(SPh)2 /Cp2Mo(SH)2 3.Cp2Mo(bdo)/Cp2Mo(bdos) 4.Cp2Mo(EDT)/Cp2Mo(PDT) II. Parallel studies of other metal complexes: Cp2M(bdt) M=Cr, Zr,Nb, etc. III. Extended studies on 1e- oxidized d1 M(V) [Cp2Mo(bdt)]+ and [Cp2W(bdt)]+. - Determine methodology for synthesis, isolation and purification of complex. - Physically characterize species (MS, CV, IR, EA, XRD) - EPR - DFT calculations. Note: The most studied complex is Cp2Mo(tdt), with UV-VIS/IR/XRD/NMR. The XRD (disordered structure?) paper did not describe how this complex made. A paper found did describe syntheses of the W and Mo tdt complexes by reacting the Cp2MCl2 precursor with dithiol in presence of NaOH (solvent?) The Cp2M(bdt) Mo/W have been synthesized, but only characterized by XRD (the W paper did not describe or referenced a syntheses; the Mo paper was in German, and gave a limited synthetic procedure summarized in abstract using halide precursor with dithiol, TEA in aq. benzene). A paper with XRD on

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Cp2Mo(bdt-C(C=O)NH2) with derivitized bdt ring was made with halide precursor in benzene, and Na salt of the dithiolate in water added to suspension. The late spring/initial summer of 2002: The following have been synthesized and identified by MS in the crude and isolated products. The following were sucessfully synthesized (but with poor yield,sluggish reactivity, complications with sideproducts and decomposition, and w/r to purification and stability with these conditions) initially from a general method, the halide precursor suspended in dry-degassed toluene under Ar, with dithiol in presence of base TEA (dried,distilled under Ar) added, or for 1 case no base added but directly with Na2edt, and heated to ~70degC in oil bath for a prolonged periode of time (~1-2hrs min/max overnight). Several trials with slight variations (diff times etc) were performed for Mo(bdt) and on Mo(bdtCl2) using this method. The initial TLC profile showed that tol alone was not suffient to separate out the raw reaction components for silica gel collumn. THF and or MeOH was found to effect separation (THF byitself, Tol:THF 10:1; and with later preps tol:MeOH 5:1) but generally required 2 diff collumns since still appeared to be trace impurities by subsequent TLC that may reflect decomposition in solution or from collumn. The overall results were very low yields were obtained, and probably reduced further upon collumn purification with silica gel (for both low reactive as is and in highly activated by drying in oven). The presence of sideproducts/decomposition identified/isolated (e.g Cp displacement to form CpMo(bdt)2]- resulted in a blue band isolated on collumn from raw reaction mixture identified by MS; also bisdisulfide presence in sample collected from collumn in XRD sample, 1 volatil component observed to come off at ~30degC under vac at ~10-7torr in PES of bdt complex, there being only that~170deg for the compound below 210degC.) Our previous experience with Mo dithiolenes was to have very dry and deoygenated conditions and thus employed usually dry nonpolar toluene at elavated temp for ligand exchange of dithiol in presence of base or directly with salt of dithiolate with halide precursor. The nonreactivity of halide precursor in these Cp2Mo systems in solvents such as tol/benz/dcm with thiols/base or directly with salts of thiolates (say vs Ti analogs has been commented on previously due to diff e- occupation, as the 2e- Mo dication halide species will react with thiol under these similar conditions) however, the neutral Mo halide species were found to react with thiols in base in solution of EtOH/water, but this has never been commented on. That we were able to make the edt complex in dry toluene but at very low yield is significant. The observation that the syntheses of the W and Mo dithiolenes also for various routes use aq. Solutions of some sort, and may also use np solvents such as benz that is wet. Again, nothing has been discussed as to why. We finally went to aq. Toluene solutions at ~70degC that did improve the reactivity with dithiols, Mobdt and WbdtCl2 reactions were tried. However, the optimized syntheses described below for the bdtCl2 complex of Mo required extreme exclusion of oxygen at all stages, and with benz/water added at reflux, dithiol/base/ reaction was fast occuring with high yield within 1 hr, with very little impurities upon washing and several filtering proccesses anaerobically to ensure no decomposition products and excess reactants. TLC suggest very pure, only 1 spot with benz. Q is does diff solvent mixture such as benz/MeOH show more than one species, Q does using florisil vs silica gel reduce decomposition on collumn e.g. disulfide formation? The most important aspects of this is that the product formed is extremely sensitive to oxygen and apparently to sideproducts, excess dithiolate, and must be separated from these (what is mech of this problem?) The 2 Mo/W bdt complexes were resynthesized/with this diff procedure. Obtained new crystal structure for Cp2Mo(bdt) in MeCN (-5degC)at very high resolution, to employ in our high level DFT studies (Huckel ect basic calc used previously for majority of Cp2 systems). This Mo complex, whose crystal structure was solved by Hemant (said to be the best/highest resolution crystal ever submitted by this group)also submitted for HeI PES/ and DFT calcs via Hemant. Note: A bis-disulfide of bdt was also present in sample that was also resolved in this crystal structure study. The crystal was derived from from initial syntheses, multiple collumns,(the same sample submitted to PES HeI), and then a 3rd collumn using florisil(DCM/MeOH), then the anaerobic crystalization. (A later syntheses employing aq. Toluene, and a florisil collumn was used to prepare Cp2Mobdt sample for close up HeI and HeII published in PNAS; Joshi, cooney, inscore, gruhn, licht, enemark; NOTE, I had planned from the beginning to publish this and the other complexes together in a single paper, but this was not the case, and thus a considerable amt of work and effort was delocalized and diminished)

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Cp2Mo(bdtCl2) is new complex/synthesis. Attempted top grow crystals for XRD in MeCN at –5dec C as was done for bdt analog in this study, but failed. Samples from the 1st were submitted for HeI; HeII was also collected later from 2nd/ and 3rd syntheses with Hemants assistance. EA in DCE (with epsilons )was aquired by the OLIS and the methodology for obtaining such accurate data was demonstrated to Hemant who observed and assisted here for experience to perform his own measurements in future. Cp2Mo(qdt) is new complex/synthesis. How far do we pursue? Cp2Mo(edt), has been resynthesized/ with this procedure, with assistance of Pablo, there is little data reported for this complex(MS/NMR,IR); XRD and PES studies essential as this is a true ene-dithiolate, and thus will resolve issues regarding aromatic dithiolates, e.g. complexity of the dithiolate ring vs S-C=C-S edt. Different Electronic structures? The W analog also reported, are we interested? Cp2Mo(tdt) was resynthesized/ with this procedure by Hemant/ MS of crude product identified this; however, upon eluting on a collumn, a band was isolated that was thought to be product (without MS verification) and with great difficulty (as a oily material was the product) via pumping in vac for long periode, the sample submitted for PES HeI was obviously decomposed. This compound has yet to be resynthesized. Cp2Mo(bdo) was also attempted by Hemant using this procedure diff from that reported and failed according to MS. Cp2Mo(qdo) a new complex was also attempted by Hemant, but not pursued further. XRD studies on any of these types d2 or oxidized species are important as majority of such info is limited to dmit and other S-rich ligands (Formague). There is only 1 example of M(IV)/M(V)+ XRD see Fourmague. Initial reactions: all target compounds identified by MS of crude ESI in MeCN and/or FAB+ Cp2MoIV(Cl)2 (250mg, mmol) in toluene (20 ml) + H2(bdt) (.107 ml, mmol) + NEt3 ( ~.3ml, mmol)70degC yielded Cp2MoIV(bdt) + 2(ClHNEt3) Cp2MoIV(Cl)2 (250mg, mmol) in toluene ( 20ml) + H2(bdtCl2) (.178g ml, mmol) + NEt3 ( ~.3ml, mmol) 70degC yielded Cp2MoIV(bdtCl2) + 2(ClHNEt3) Cp2MoIV(Cl)2 (250mg, mmol) in toluene ( 20ml) + H2(qdt) ( 0.1636g,ml, mmol) + NEt3 (0.25 ml, mmol) 70degC yielded Cp2MoIV(qdt) + 2(ClHNEt3) Cp2MoIV(Cl)2 (250mg, mmol) in toluene ( 20ml) + Na2(edt) (.1146g, ml, mmol) 70degC yielded Cp2MoIV(edt) + 2(NaCl) Disodium ethylene dithiolate (0.0.11g, 0.81 mmol) was prepared immediately prior the reaction and dried under vacuum to avoid decomposition products. The purified, dry ligand was placed to a 250 ml schlenk flask equipped with stir bar along with Cp2MoCl2 (0.250 g, 0.84 mmol) and dried in vacuo. Dry, deoxygenated toluene was transferred to the reaction flask by syringe and the mixture was stirred at 70º C for 20 hours under an inert atmosphere of dry Argon gas. Characterization of the desired synthesized product has been confirmed by mass spec. Cp2WIV(Cl)2 (300mg, mmol) in toluene ( 22ml) + H2(bdt) ( .110g,ml, mmol) + NEt3 ( ~.3ml, mmol) yielded Cp2WIV(bdt) + 2(ClHNEt3) Cp2MoIV(Cl)2 (250mg, mmol) in toluene ( 25ml) + H2(bdt) ( 100mg,ml, mmol) + NEt3 (.3 ml, mmol) + H2O ( 15ml) yielded Cp2MoIV(bdt) + 2(ClHNEt3)

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Cp2WIV(Cl)2 (305mg, mmol) in toluene (25 ml) + H2(bdtCl2) ( 0.165g, mmol) + NEt3 (0.22 ml, mmol) +H2O (15 ml) yielded Cp2WIV(bdtCl2) + 2(ClHNEt3) Cp2MoIV(Cl)2 (500mg, mmol) in benzene ( 50ml) + H2(bdtCl2) (.354g ml, mmol) + NEt3 ( ~.5ml, mmol) +H2O ( ml) yielded Cp2MoIV(bdtCl2) + 2(ClHNEt3) 50 ml of degassed benzene (deoxygenated prior to reaction by a combination of Ar saturation and FPT cycling) was transferred anaerobically by steel cannula to a pre-purged/evacuated extended neck/pear shape 14/20 100ml Schlenk reaction flask (with magnetic stir bar) containing 500 mg (1.68 mmol) of dry Cp2 MoIVCl2 and~ 355 mg (354mg, 1.68 mmol) of the H2( bdtCl2) proligand. The reaction flask/mixture/stirring suspension/solution, upon each addition or transfer to it under a pos Ar press was subsequently purged gently with several cycles of pumping under slight vacuum for a short time and Ar sa to ensure oxygen free enviroment is maintained. (The dithiol can be introduced to the reaction flask either directly prior to solvation as done here(H2bdtCl2 being a solid at RT) or following solvation the solid added to the stirring precursor suspension at RT/ or transferred to the reaction mixture in a solution/suspension of the appropriate solvent). The rigorously stirring reaction mixture under a positive Ar pressure was slightly heated (~30deg) and affected by 0.5ml of dry-deoxygenated(prepurified by distillation over Na/K amalgam under inert atm of dinitrogen/collected under Ar, degassed by several FPT cycles, and sat with pos press of Ar prior to transfering ) TEA( 0.47ml, 340 mg ,3.36mmol) via a gas tight syringe, followed by 10 ml of pure deoxygenated (Millipore Water purification system (18ohm res), previously bubbled with Ar for 2hrs /sat with Ar in schlenk flask for 20 min intervals followed by purging with pos Ar flow to ext atm provided by a syringe needle in septum )water in a similar fashion, and the mixture subsequently brought to reflux (with flask submerged so that solution (slightly greater than half flask volume) is slightly below mineral oil level; oil bath heated to T~69°C) using a single isopropanol- cooled reflux condenser attached to the reaction flask, and connected to a Ar line/ mineral oil bubbler /overpressure external release system optimally designed for providing, maintaining and controlling a constant blanket of Ar in a psudoclosed environment, at slight pos press, for such reactions requiring an inert atm free of air be maintained. The initial green suspension was observed to change color to red/brown within ~15 min upon refluxing under slight Ar pressure. The initial solid material observed in the reaction appeared to be consumed within ~1 hr of refluxing. The reaction mixture containing two distinct solvent phases(benz-org component on top, aqueous layer on bottom was filtered anaerobically (hot?) into a sep shlenk flask, where the benz component was separated by direct removal of the aq. layer. The benz layer was subsequently washed with 20 ml (2x10 ml) of deoxy/Ar sat water and subsequently sep by remov of the resulting aq layer. The benz filtrate was filt anaerobically into a react flask, and under repeated Ar purge /evacuation/sat cylces was slowly reduced in volume, followed by solvent removal accomplished by anaerobic evap(schlenk flask transferred under Ar to customized air-free solvent removal system employing a dry ice acetone cooled solvent sep/collection/isolation device and LN2 trap connected to a vacumm manifold and subsequently heated in oil bath) to dryness in vacuo, and pumped on several hours to ensure complete removal of volatils. The solid residue( 2 distinct layers red-brown coated on side and bottom and gold brow loosely laying on bottom following solvent removal where gold brown layer physically removed from flask) was TLC in benz etc , see only 1 spot;(is this really only component, need to check other solvent mixes) then resolvated in DCM, filtered, and solvent removed under vac to dryness(, check TLC if changed?MS? repeat); check Tol:MeOH 5:1 (or THF) TLC for comparison to previous. Extract with benz, and purify by Florosil collumn.

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Preparation of Cp2Mo(S-S) Paper: Formulation and Development General Considerations Goals and objectives of our study: What are we studying and why? How will we study and what do we hope to get out of it? Significance of our paper: How is it important/unique? What specific contributions can we offer that has an impact or provides new insight? Background Develop the importance/relevance of this study using these model systems. 1.What is our previous and ongoing research focused on? What do we wish to achieve? How do we go about it and why in general? 2.How is this model system and specific models employed relevant and what additional insight can they provide, with respect to our previous studies and other model systems ? Why the specific primary models in this study were targeted. Develop specific issues/ problems to be addressed, and the methods/techniques to be employed. 1.What is known about the physical and chemical properties of these and related models of this system type in general: regarding availlability and characterization methods; and interpretation of/ or insight from data regarding contributions to bonding and geometric/electronic structural relationships. How does this relate to our research goals, interest in this system,and choice of specific models/physical methods employed in the current study.

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2.What, why and how are our studies/ methodologies/probes of our specific models important/ relevant/novel? Can they provide additional/ useful or new insight that is significant/unique w/r to our research interest and/or contribute to the understanding of this system type? 3.What other issues and implications evolved from our preliminary studies and what was required to futher probe/address these. General and Specific Background/Issues: outstanding/ to be resolved Background/Issues relating to pyranopterin Mo/W enzymes A.Structure/function/reactivity 1.get all papers/ect on XRD of Mo/W enzymes q.What is ox state/resolution/features and what do we get out?Insight into what? Limitations/implications? q.What is availlable/accessible in PDB; what can we extract/manipulate or not? 3.XAS/EXAFS on specific systems i.e.SO/monoene, q.What oxy states and what do we get out? Insight into what? Limitations/implications? q.How do these relate to xrd results? Other spectroscopic results? 4. EPR on specific systems i.e. SO/monoene q.What do we get out of these in general? Insight into what? q. How relates to other structural/spectrscopic/electronic/reactivity/mech insight? 5.other spectroscopic techniques UV-vis abs/ rR/ MCD etc in particular for SO/monoene q?What oxy states? What do we get out? Insight into what? Limitations/implications? B.Specific questions and statements 1.What is consensus of active site structures during course of catalysis? Common structural patterns? 2.a.Postulated Roles of pyranopterin-dithiolate? Other new/potential roles evolved b.How does it control/ what factors affect/determine its role/contributionsDuring course of catalysis? 3a..role of monooxo following oat on et? Oxogate hypothesis? -Is +4 so/xo o-m-s ~90deg, what role does +5 play in this, can it probe this ,see so mcd studies role and implied geometries and w/r to +4. note- no direct structure of intermediate anywhere, very limited struct data(and electronic data) on +4 states in particular w/r to geom. -for DR +4 is resting state d2 desoxo, ( +5 desoxo d1),following oat +6 is d0 monooxo prior to et(put e- in to regenerate) do we have any o-m-s angle data ect? b.geo/elect relationships-contributions w/r Sip-Mdxy vs Sop-Mdxy interaction on ET pathway, modulator of redox, oat ect. c.What is the mechanics? How/what affects contributions to dxy/ homo-lumo during catalysis?Sip vs Sop d.What is implications/role of dynamic fold angle during course of catalysis? Sip vs Sop/d2vsd1vsd0/ w/r to no significant changes in inner coord (remains isostructural for 2 or all states; not like =O to oh2 ect) or metrics. What about between the two states with structural changes as above due to nature of reaction?How does o-m-s angle >90 deg and role in oxo-gate mean with folding? e.How doesSop relate to foldangle/ e-buffer effect-axial changes/ox changes (note as all others have a terminal oxo at 6/5/4 only DR +4/5 does not have terminal oxo OvsOH/ SO-XO see some changes 2term +6 1termoxo+5/4), mod redox pots/ interactions with dxy ET, interactions with dxz,yz for oat etc. 4.a.no uvvis or electronic insight on SO Mo(+4) d2 mono-oxo/mono-dithiolene diamagnetic site?XO +4?Structural insight on +4 via XAS(EXAFS) b. Majority of what is known about electronic structure in SO (and for thatmatter most enzymes) comes from epr of +5 paramagnetic site, +6/+4 (/+5) difficult to probe by abs/rR etc due to additional redox groups (heme) that interefere/obscure the Mo center spectra. no clear structural insight on Mo(+5) SO no xrd etc., structural insight derives from epr on site and comparison to models. assumed Mo(+5) d1 mono-oxo-monodithiolene paramagnetic site? c.Key factors/geo-elect relationships/ contributions to reactivity of reduced +5/+4 monooxo/monoenedithiolate? Very little is known about electronic structure of + 4 mono-oxo/mono-

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dithiolene site, which is important w/r to ET regeneration of resting +6 state following formal OAT. +5 mono-oxo/mono-dithiolene intermediate also important as it lies along the catalytic pathway during turnover. Fact is very little known about geo structure/ stereochemistry of +4/+5 sites as no XRD yet (In fact No XRD has yet to be reported for any Mo/W metalloprotein +5 active sites in any family). d.consider, have 5-coord dioxo d0 +6/monooxo d1 +5 mono dithiolene isostructural mononuclear Mo models of SO, also 6-coord mono-oxo d1 +5 monodithiolene mononuclear Mo model system, no mono-oxo d2 +4 monodithiolene models isostructural with +5 models, and in fact no mono-oxo-mono-dithiolene +4 mononuclear Mo models of any sort reported at present. -what about +4 mono-oxo Mo models of any sort? 5-coord mono-oxo-bisdithiolene Mo/W +4 and their isostructural +5 analogs exist; 6-coord TpM mono-oxo models are known in +4 with mono-1-1 dithiolate (no +5 isostruct analogs?), mono- thiolate (any +5 isostructural analogs?); any others of this Tp* type? what about any others of any type? -what about +4 mono-dithiolene Mo models of any sort? Cp2M(IV)(S-S) is to best of our knowledge the only known mononuclear Mo(/W) d2 M(+4) mono 1,2-dithiolene system reported? *This system possesses isostructural d1 M(V) analogs/ also may be possible to generate d0 M(VI) analogs as well; this is relevant as this provides an isostructural system for all 3 relevant states, I don’t believe any other such isostructual 3-componentsystem for Mo/W in particular with dithiolene coordination, with the exception of CpM(+4/5/6)(S-S)2]-1,0,+1 system? However, note that active sites are generally limited to 2 closely isosostructural active sites: +4/+5(w/r to ET regeneration of +6 from +4 ) mono-oxo/mono-dithiolene in SO/XO( 3S(2S//-S-S- + 1S//-SR,=S)and 2O(1O//=O + 1O//=O,-OR) in all states in SO(oxo/oxo//S-S,Scys +6, oxo-OH(OH2)//”” +5/+4) and XO(oxo/sulf//S-S,OH2 +6, oxo-SH//”” +5/+4 ), common/minimal structural feature is mono-dithiolene for +6/+5+4 in SO-XO/ in addition to 1S-S, at least 1 terminal oxo present note:only 1terminal oxo is present in reduced states); and +5/+4 (w/r to ET regeneration of +4 from +6) desoxo/bisdithiolene in DR (4S(2S//-S-S- +2S//-S-S-) and 2O(1O//Oser +1O//OR,=O in all states DRrs,rc), common minimal structural feature is bis dithiolene for +4/+5+6 in DR, note: no terminal oxo is present in reduced states). *Common structural feature in Mo enzymes is the pyranopterin-dithiolene cofactor, and the presence of 1S-S is the minimal structural feature. Determining the role of this unit in catalysis, and how it defines the elec/geo structures and relationships, in particular w/r to M-S bonding contributions to reactivity. Thus any mononuclear TM-dithiolene systems are of interest (generally possess mono/bis/tris S-S; most interested in mononuclear M-dithiolene systems with M=Mo/W centers, and in particular d0 +6/d1+5/d2 +4, with 1/2 S-S units relevant to enzymes and represent the minimal structural/ electronic features; an additional minimal structural feature is also a terminal oxo ). So why/how are CpM(S-S) systems relevant and important? What insight can we gain from them and regarding what in particular?? 5.a.Cp2M(S-S) -mononuclear Mo/W centers in relevant +6 d0/ +5 d1/ +4 d2states possessing minimal structural feature an S-S, in particular 1S-S very relevant to SO/XO. Regardless, stillminimal feature is 1S-S in enzymes, and is starting point/simpler system for understanding 2S-S complexes relevant to DR (why 1 vs. 2S-S?, effects of 2nd S-S, etc). Also this is simplest system availlable, in particular for mono-dithiolenes to understand M-S effects etc. Isostructural series w/r to oxy state, nature of S-S,nature of metal Mo vs W; allows us to probe M-S interactions w/r to each of these effects independently and in combination to elucidate geo/elect structures, their relationships , and how these effects affect/define the molecular physical and chemical properties (geo/electronic/echem// stab/reactivity) of the molecule w/r to M-S bonding. Although 1S-S is relevant to SO, SO also posseses a term oxo (only one oxo and S-S for reduced +5/+4 states). While thereare a limited number of relevant mononuclear d1 Mo(V) mono-oxo mono-(S-S) complexes, there are no relevant d2Mo(IV) mono-oxomono –dithiolene complexes (and thus no isostructural +4 analogs of the +5 complexes). The limited insight of the SO reduced sites, in particular the +4 site, makes such models, and in particular isostructural +5/+4 analog series desirable and important. Whilethe d1 +5 mono-oxo mono S-S complexes provide some insight into the d2 +4 site(w/r to geo/electstructure) they only provide an approx as expect zeff of M, geo and elect properties to change as e-occupationinc d1-d2, , and the absence of relevant +4 MoO(S-S)analogs precludes understanding how and to what extent this change is manifested between the 2 states as a function of oxy state. There are mono-oxo d1M(V) andd2 M(IV) isostructral

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analogs that contain two dithiolenes, that allow some insight into effects of oxy state change, but are more complicated due to 2nd S-S, and are relevant more to DR, vs SO w/r to number of S-S units (but really relevant only to d0M(VI) in DR as the reduced sites contain no terminal oxo,and thus are more relevant to SO reduced sites vs DR reducedsites w/r to presence of single terminal oxo). Thus the d2 Cp2M(IV)(S-S) system type provides the only known Mo(IV) monodithiolene complexes availlable for studying M-S bonding interactions relevant to the reduced site of SO, and the ability to generate the d1 Mo(V) monodithiolene isostructural analogs is also important for probing geo/electronic relationships and contributions in a controlled environment with monoene-1,2-dithiolate coordination as a function of oxidation state (e- occupation), and being simple system is advantageuos as Cp rings –and their effects appear invariant and enrgeticaly innocent, allowing the study of a isoltated M-(S-S) unit not affected by a terminal oxo. 6.a. no +5 desoxo models/ or no relevant data –inferences. How does +4/+5 desoxo/bis electonic/geo structure impact vs mono oxo/bis / how affects monooxo+6/bis after oat? b.consider 3a. SO resting state+6 O2S-SSr d0 to (+5 O(OH)S-SSr d1) oat +4 O(OH2)S-SSr d2 prior to et (remove e- to regenerate +6) while for DR +4 is resting state d2 desoxo, ( +5 desoxo d1),following oat +6 is d0 monooxo prior to et(put e- in to regenerate +4) How does fold angle w/r to e-occupation/ diff electronic structures work here (oxogate says o-m-s = 90 following oat , fold angle should be large for d0 vs d2). Is fold in DR +6 larger than fold in DR +4 and SO +4? Q is what is role of fold in ET regeneration?OAT?if any. What effects does fold play in the electronic structure during turnover as in both DR and SO see structural changes which must change electronic structure +6O2 d0/5Od1/4Od2 SO vs +4desoxo d2/5desoxo d1/6 O d0 DR 6. Background/Issues relating to biomimetic models of active site 1. Background/Issues relating to general metal-ene-1,2-dithiolate 1. Background/Issues relating to specific/relevant M(S-S) systems A.mono 1.Holm SO +6O2S-S(SR)X/+5OS-S(SR) B.Bis 1. C.tris 1. D.organometallics mono/bis Issues specific and relating to Cp2Mo(S-S) and Cp2M(S-S) system type A. Fold angle correlations/trends/relationships A.questions 1.Is fold observed in each of the various types comprising the Mo(S-S)/(S-S)2/(S-S)3systems above? Tabulate for each system (mono/bis/tris) /system types(+6O2/+5O/+4O bis;+6O/+4OR bis;;+6O2SR/+5OSR mono; Tp*MoO(s-s) +5 – isostructural/related series, and as function of oxy state (e- occupation), type of s-s bdt vs qdt etc/ change in coord or axial(S vs NO)/ change in geom type Cp2 /Cp/ change in metal Mo4d/W5d/ other isostructural analogs with diff metals(Group IV3d4d5d/V3d4d5d) will be considered later e.g. Ti vs Mo, in Cp2/Cp systems are availlable etcdiff e-occupation for same oxy state. -can we look at known or potential isostructural series with given geometry/electronic structure that allows us to probe fold: for given metal ,oxy state and S-S: mono S-S 1 a. d1Tp*Mo(V)O(bdt), b. d1 Tp*Mo(V)S(bdt),, c. d4 Tp*Mo(II)NO(bdt)/ d5 Tp*Mo(I)NO(bdt)]-; bdt,tdt,bdtcl2,edt,qdt d1 Tp*W(V)O(bdt)

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d2Cp2Mo(IV)(bdt)/d1Cp2Mo(V)(bdt)]+/?d0Cp2Mo(VI)(bdt)]2+ ; ?Holms d0 Mo(VI)O2(SR)(bdt)]-, d1 Mo(V)O(SR)X(bdt)]-; Our interest w/r to pyranopterin Mo/W enzymes, is primarily focused on the active sites of mononuclear Mo enzymes in their catalytically relevant Mo(VI/V/IV) oxidation states, which possess a single pyranopterin coordinated to the metal via the 2 sulfur donor atoms of the ene-1,2-dithiolate linkage (XO and in particular SO). The common structural feature observed in all reported crystal structures is at least one pyranopterin-ene-1,2-dithiolate cofactor coordinated to the metal center and represents the minimal structural feature of the Mo active site. Studies directed towards understanding the chemistry, molecular structure and electronic properties of Metal-ene-1,2-dithiolate systems are clearly important for understanding the role of this ligand regarding M-S bonding interactions relevant to the enzyme active sites. -static oxy state (Tp*Mo(V)O(bdt), consider how the magnitude of the fold(deviate from planarity;158.7<180,-21.3) in conjunction with O-Mo-S (deviate from Oh; 100.9>90, +10.9) affects bonding (our MO diagram, in particular w/r to M-S bonding)and experimental observations: S-M CT dxy/dxzyz E/int ; red pots; pes IE. Run calcs on O-M-S 90-120 0-30 no stab of Sop lower vie/lower ct to xy, no destab of xy more pos red pot/higher vie but better interaction with xzyz inc ct int xzyz,, stab of sop, destab of xzyz maybe, dec zeff dec red pot lower vie, sip-mxy destab of xy/stab of sip inc ct int with xy, inc energy, more neg red pot lower vie I. Synopsis II. Title/Authors/Correspondence III. Abstract IV. Introduction V. Experimental Section A.Materials and Methods 1.Conditions-Methodologies- Procedures/Techniques a. general protocols: synthetic manipulations/ characterization sampling/preparation-purification b. inert gases/solvents/reagents/chromatographic materials/materials employed in characterization c.Commercial precursors,ligands, and other starting materials, reagents 2.Fig(V.1) General coordination Cp2M(S-S) complexes/ dianion dithiolate ligands/ abreviations B.Preparation of Complexes 1. Preparation/purification/characterization of a. reaction Solvents 1). Benzene (/toluene) purify Omnisolv or drisolv over Na/K, reflux/ distill over and under N2//collect//transfer to shlenk flask under Ar/Vac employing manifold/line directly from stills. Sat with Ar via bubbling/ purge-pump several cycles/ FTP several cycles/sat flask with Ar 20 min/ purge-pump several cycles before use// transfer via steel canulla (or syringe?) to reaction flask or addition flask. -char purity by NMR/IR/MS 2). Water Obtain from nanopure source (18 ohm) // sat withAr bubbling/ purge-pump/ sat with Ar//FTP? And or more purge-pump/ sat with Ar/ transfer anaerobically. -char purity by NMR//properties tlc/collumn material-florosil/silica gel (evac-dried?) 3). Other solvents used in separation/extraction/purification/recrystalization/characterization (a). DCM/DCE (b). MeCN

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(c). Pentane/heptane/cyclohexene (d). MeOH/EtOH/THF/Et2O -dry/deoxygenate// char purity by NMR/IR b. other reagents/ materials 1). Et3N(l) Purify over Na/K, distill under N2// transfer anaerobically// sat-purge-pump-ftp etc before use. Char purity by NMR/MS/IR etc./ properties-stability in reaction solvents :benz/ water/ benz +water/O2-water sensitivity/solubility etc. TLC/collumn materials/abs 2). NaOMe(s), NaOH c. precursor complexes (Cp2M(IV)Cl2) (M = 4d2 Mo/ 5d2 W//4d1 Nb// 4d0 Zr/ 3d0 Ti) (and associated fragments: Cp-/ Cp2Mo/ Cp2MoH2/ Cp2Mo(SH)2) d.proligands: dithiolate (S-S)2- ; isolated as protonated//salts of dianion 1). dithiol (S-S)H2 (S-S) = bdt/tdt/bdtCl2//qdt 2).dithiolate salts (S-S)Na2 (S-S) = bdt/qdt/edt 2.Preparation/Isolation/Purification/characterization of neutral Cp2 MIV(S-S) complexes. a.M= 4d2 Mo(IV), S-S = 1). bdt (ref synth.; modified synth.) 2). a).bdtCl2 (new) b). tdt (ref) 3). edt/ (?edtMe2) (ref/ (new)) 4). qdt (new) b.M= 5d2 W(IV), S-S = 1).bdt (ref synth; modified synth) 2). bdtCl2 (new) 3). (?edt/ ?edtMe2) (ref/ new?) c.M = 4d0 Zr(IV), S-S = 1). bdt (new ) 2). (?edt/ ?edtMe2) (ref/ ref?) d.M = 4d1 Nb(IV), S-S = 1). bdt (new) 2). (?edt/ ?edtMe2) ( new?/ ref?) e.M = 3d0 Ti(IV), S-S = 1). bdt (ref/ref JJC) (note: ref. JJC results of what is needed for comparison) 2). (?edt/ ?edtMe2) (ref / new ?) 3.Oxidation of Cp2M(S-S): Preparation/isolation/purification (attempt// failure/why ? or success/how ?) a. Cp2 MV(S-S)]+ M = 4d1 Mo, S-S = bdt? (new) (note: maybe some other S-S =?; ref dmit works) b.Cp2MVI(S-S)]2+ M = 4d0 Mo S-S = bdt?? (new) (note: ref SPhMe/SMe shown to work) c. Cp2 MV(S-S)]+ M = 5d1 W, S-S = bdt? (new) (note: maybe some other S-S =?; ref dmit works) 4. additional Cp2Mo(IV)(Y,Y) compounds (optional) a. bdo// bdo,s b.EDT//PDT c.SR// R = H, Ph, ect. 4.General Physical Properties/ Characterization results tabulated a.how char./purity/yield/stability/identity/properties (color/melting point ect.) b.other char.reported In addition to (ms/ir/cv/uv/(nmr/epr/)//xrd//pes) (rR/MCD)? c. Elemental analysis//MS//IR(KBr/DCM)//RT/VTNMR:HNMR/CNMR//Abs//CV// C. Physical Characterization Methods/Instrumentation 1. General purity/identity/structure (geometric/electronic properties) a.MP apparatus/ elemental analysis b.GC-MS// HR-MS(FAB-ESI) c.IR(RTsolid – solution) d.NMR(RT/VT 1H-NMR; RT 13C-NMR) e.CV(solution) f.Electronic Absorption(RT solution-mull-thin film) g.Gas-phase PES (HeI/HeII/NeI)

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h.CW-EPR(RT-solution / 77K Frozen solution) 2.Structure(solid) single-crystal XRD a.Cp2Mo(IV)(bdt) new (see old bdt(ref)) b.Cp2Mo(IV)(S-S) S-S = (see old bdt, tdt(ref)), new: bdt,bdtCl2//qdt//edt c.Cp2W(IV)(S-S) S-S = (see old bdt (ref)), new: bdt, bdtCl2 d.Cp2M(bdt)]0/+1/(+2) new: M=4d2/1/0 Mo(IV/V/?VI)/ 5d2/1/(0?) W(IV/V/(?VI)) e. Cp2M(IV)(bdt) new: M=4d0 Zr, 4d1 Nb 3.additional characterization a.resonance Raman studies(RT/LTsolution-solid// 77K frozen solution-solid) 1). vibrational (non-resonance//pre-resonance/on -resonance) between ~1000 – 350 nm energy region. 2). depolarization (solution) 3). excitation profiles of vibrational bands observed in energy region probed. b. LT MCD(VT(300-1.85K)-VH(0-7T) glass-mull) of paramagnetic d1 species (particular focus on 4d1 Mo(V) benchmark ) c.LT electronic absorption (VT(300-77-5K) glass-mull-) D. Computational Methods 1.Models(neutral M(IV)//cationic M(V)/(VI) oxidized species)/ ligands (neutral//dianion) theor. Studied with ADF (ADF version 2000.01) 2.geom optimized/xrd coordinates// URS/SRS 3.references/supplementary information (tables) VI.Results A.Syntheses//stability/reactivity 1.reactivity differences d0 vs d2: reaction route to Cp2M(IV)(S-S) from Cp2M(IV)Cl2 +H2(S-S)/Et3N (or directly from (Na2(S-S))) +Org. solvent(e.g. toluene) gives very low yield for M=group-VI Mo/W 4d2/5d2 vs. group-IV Ti/Zr 3d0/4d0 (while somewhat lower yield than group-V 3d1 V/ 4d1 Nb). a. Based on Cp2M(IV)(SR)2 studies, where Group IV-d0 Cp2M(IV)Cl2 precursors react quantitatively in organic solvents with alkali metal thiolates to yield corresponding bis-thiolate complexes, Cp2MoCl2 observed to behave differently as no reaction in benzene or DCM with NaSR occurs, and subsequently should not react directly with dithiolate salts either. However, Cp2Mo(IV)(SR)2 complexes were prepared from Cp2MoCl2 and thiols (HSR) in mixture of EtOH/h2O in presence of a stoichiometric amount of NaOH (Q. was significance of H2O discussed? ). Further, 16e- d0 Cp2Mo(VI)Cl2]2+ and W analog, prepared by oxidizing the 18e- d2 neutral species (3 equivalents of AsF5 in SO2), reacts directly with NaSR to give Cp2Mo(VI)SR2]2+, (or by ox the neutral d2 bis thiolate directly), while the neutral species does not react directly with thiolate salt. Thus the 4d0 configuration of the 16e- Cp2Mo(VI)Cl2]2+ dication behaves similarily to the isoelectronic 4d0 Cp2Zr(IV)Cl2, and different reaction behavior between the d2 Cp2MoCl2 and d0 Cp2MoCl2]2+ may be explained/attributed by the different e- distribution in the two Mo species. Compare electronic structures: Consider 4d0 Cp2Zr(IV)Cl2 (and 4d0 Cp2Mo(VI)Cl2]2+); as 16e- d0, the LUMO is unoccupied, and this MO (a1) is essentially nb in character, and the base RS- may coordinate to the 16e- fragment followed by elimination of Cl- (2x) to give 16e- bisthiolate dication/ (what is nature of HOMO? Cl based or M/ what are the changes(geo/elec) upon substitution of S for Cl?) Now consider in 18 e- neutral d2 Cp2MoCl2 the filled a1 orbital now represents the HOMO, and the unoccupied LUMO has strong AB character (putting e- here to form pentacoord 19e- followed by elimination of Cl- to give tetracoord 18e- / then repeat/ prevents good bonding interaction as this MO is AB. Q. is going from d0 to d2 is the MO diagram the same for either configuration? What about Cl2 vs SR2 vs S-Sdithiolate on bonding (geo/elec changes for given oxy state, and as oxy state changes) note calcs for d2 Cl HOMO very covalent, mostly metal dx2? %Cl= vs nearly S in bdt complex; EPR of d1 95,97Mo hyperfine 36G Cl vs 10.8 g supports HOMO S-S based. QQ. How does the electronic structure change going from 4d2 Cp2Mo(IV)Cl2 to4d2 Cp2Mo(IV)(S-S) prior to/during reaction/following ligand exchange of 2Cl- with S-S 2-; what does this say about reactivity/stability/mechanism/ reaction conditions/products while either route goes readily forward for G(IV) metals such as Ti(IV) in organic solvents (H2bdt + base/Na2mnt) we observe both routes to be very low yield in org. solvent (tol), slow conversion(24hr+), and requiring heat (50-80 deg C) for Mo(IV)/W(IV) in contrast to Ti(IV) reflects origin (e- occuption trend, d0 more reactive; see Cp2MoCl2]2+ (or SR2 analogue) can form directly the Mo 4d0 dication bis-thiolate/dithiolate species from such routes). Thus either H2O must be employed (see huge shift in reactivity; rate inc, time dec, lower temp, ect.) or convert precursor to a more reactive d0 species.

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Why reactivity/stability differences,: origin of low yield in d2 vs d0 , or that H2O added /or precusor ox. to do to get inc. in reactivity for the Mo(IV/VI) reactions. 2.Cp displacement occurs for both Ti/Mo IV dithiolates, only reported for Ti, S-S specific; does occur for Mo with bdt in our study forming CpMo(bdt)2]-?/IV? ;?0/V?. Why and how: origin of Cp displacement in Cp2M(S-S) by S-S ligand (in excess?) to form CpM(S-S)2 ]- ,(tris?), how to minimize via conditions of reaction?What does displacement of Cp by ligand and subsequent substitution by ligand say about the nature of the ligand vs Cp? Is displacement of Cp in Cp2M(L2) complexes dependent upon nature of Leq (Cl vs S (say vs N imido , a strong pi donor)) oxidation state M(IV?V?VI?). i.e. dont see displacement of Cp in halide complexes?/ also appears displacement depends on the nature of the S-S i.e. dont see this for all S-S with M=K (if function of e- donor properties of dithiolate S atoms, then displacement may originate from charge donation into orbitals involving Cp(π) C-M bonding , weakning the bond or disrupting the Cp(pi) interactions with the metal. 3.stability differences, disulfide bdt observed when use silica gel indicating S-S ligand oxidized in Mo complex, dissociating and forming disulfide on collumn? while fluorosil appears to minimize this for Mo d2. Cp2 Ti(IV) bdt analogs dont appear to have this problem on silica gel. Is it oxygen presence in collumn or direct reaction with collumn stationary phase. How and why is this problem for Mo(IV) but not for Ti(IV). B.IR/MS Cp2MoCl2 M-Cl 293vs/262s; Cp2MoCl2]+ 334s, 311vs; delta Cp = d2 5.67 ; d0 2+ 5.9 high freq/ low field shift from d2 neutral counterpart observed C.NMR 1. presence of Rt H-NMR signal implies diamagnetic (18e- configuration), spectral analysis of shifts/splitting reveals sample possesses only 1 diamagnetic species, which is consistent with Ar ring benzene protons, and a Cp ring protons. 2. VT-NMR H; only 1 signal observed for Cp ring as a function of temp; i.e. absence of peak splitting at lower temp implies no inversion process (flipping of dithiolate ring: such that symmetry is changed from ideal C2v (no folding of S-S) to Cs (folding of S-S) so that Cp ring protons are not equivalent. i.e in solution the C2v symmetry is not observed due to folding of S-S. In d2 complexes predict that as no inversion process is usually observed, their is no distortion of C2v geometry due folding as is the case for d0 systems such as Ti(IV). The C2v solution structure is consistent with the solid state structure from XRD, which reveals folding very small (0-9deg) or as predicted for ideal case zero.. Thus structure of solid retained in solution, no symmetry lowering, and confirms solid structure which reveals very little/or no folding of S-S. 3.C-NMR consistent with Cp2Mo(bdt) formulation and structure. D.Consider that EPR reveals no paramagnetic Mo species, indicating no partial oxidation of this complex or its precursor has occured to any extent, the absence of signal thus further confirming the diamagnetic nature of this system isolated, and hence an 18e- configuration (or 16e- if fully oxidized) but not paramagnetic (reduced 1e- to d3 Mo(III) or oxidized 1e- to d1 Mo(V). These acsessible states suggested are consistent with the corresponding 1e- transfer ox/red processes observed in the CV exps. VII.Analysis VIII.Discussion IX. Summary/Conclusions X. Acknowledgements and Funding XI. References XII. Tables/Schemes XIII. Figure Captions/ Figures XIV. Supplementary Information

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QQ. Can we derive MO diagram that explains experimental observations/trends/correlations w/r to chemical properties(reactivity/stability) and physical properties(geometric/electronic//echem) MO Diagram: Development and Evaluation Key Exp. Observations; 1.chemistry a.Reaction of Cp2M(IV)Cl2 + H2(S-S)/base// or+ Na2(S-S)// +solvent(s)//conditions(reactivity/stability/decomposition; T=,t=) requires high temp (for conversion?)/ longer reaction times (due slow rate? ) and results in very low yields in organic solvents (tol) for GVI M=4d2 Mo 5d2 W due to the stability of precursor/instability of product under these conditions in contrast to GIV M= 3d0 Ti 4d0 Zr (and GV 3d1 V 4d1 Nb) where precursor more reactive and product more stable. Reaction behavior of Cp2MoCl2 (W?) precursors in organic solvents (tol/benz/dcm) different than the d0/d1 M(IV) neutral 3d/4d G4/G5 analogs which readily react with dithiolate/thiolate salts directly and/or dithiols-thiols?/base in organic solvents. However, d0 Cp2Mo(VI)Cl]2+ does readily react with such thiolate-salts directly in organic solvents. The inclusion of aqueous organic solvents in reaction of Cp2MoCl2 and dithiol/base here (as shown previously for thiol/base //EtOH/H2O) does change all of this dramatically providing significant improvement in yield/stability-sideproducts/ and Rt (under reflux ) for d2 reactions(salts or protonated ligand/base). *What is general method/precursors for making Cp2Mdithiolate complexes with G4/5/6 metal centers? What Cp2 Mo/W dithiolates are availlable(refs). (ref their G4/G5 analogs). Goal: identify potential route-most efficient method /commercial precursors for Cp2M(S-S) syntheses (Mo/W), and identify possible complexes of a specific S-S type that have not been made or have not been characterized well-or by a particular method for future studies. *Considering that Cp2MCl2 is general precursor used to make S-S complexes, what is reported properties/reactivity/stability and char of neutral d2 Cp2MCl2 (Mo/W)? What about ox d1/d0 cation species? // How do we char to determine purity/stability/reactivity:MP/MS(ESI or FAB)/NMR/EPR/ABS/IR/CV/Solubility-temp org NP-Pol -aquous/O2-H2O sensitivity//in presence of base and particular solvents(benz, water,benz +wat,/et3n or naoh) //and ligands(H2s-s or na2s-s). Solid vs solution/ decomposition temp –products/PES HeI-II-sublimation temp/ tlc and collumn (silica gel-florosil, dry –vac) behavior –properties. //How do we purify/dry/deoxygenate etc and maintain purity? //How do we identify and remove precursor contaminant in target products? Goal: char to ensure purity of precursor/ det best methods-conditions for minimizing decomposition/ox/side reactions- inc reactivity, monitoring/optimizing reaction progress and presence of precursor, separating from target products during extraction-washing-recrystallization-collumn purificationand TLC behavior. Behavior w/r to temp, diff solvents-mixtures-reagents(bases)-ligands and time-rate. *what is reported methods and conditions for reaction d2 neutral cp2MCl2 (Mo/W) with Na salts and/or protonated dithiolate/thiolate ligands.(refs)/how characterized? Any reported oxidized cation d1+/d0 2+ isostructural species from neutral d2 parent? What is reported w/r to reactivity-stability-physical properties-decomposition-side products/reactions for G6 vs G4/ or G5 precursors -dithiolates in general/ or specific isostructural-electronic analogs. Goal: Identify known-potential synthetic route-conditions for Cp2Mo/W dithiolates reported or proposed, properties-disadvantages etc what said or not, postulate optimized synth-isolation-purification routes for our targets using Cp2MCl2 precursors. Identify key observations/outstanding issues pointed out or not – discussed/understood or not w/r to chemistry-mech/reactivity-stability and geo/electronic properties-trends for Mo/W and also differences-similarities for G6 Mo/W vs G4/G5 precursors-dithiolatetargets and/or

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origin-nature of side-decomposition products that we may address-probe,confirm,negate or redefine in greater detail-insight with further exps. Postulate and test new hypotheses and/or modify previous. Exp: Char purified reaction solvents (benz/water) and reagents (Et3N,other bases NaOH, NaOMe), precursor cp2Mo/Wcl2, and S-S ligands (H2S-S (bdt,tdt,bdtcl2,qdt) Na2S-S (bdt, edt)) to ensure purity, ability to monitor-det stability/reactivity/reaction progress/reactant-product identity- isolation- purity and specific behavior-properties. TLC behavior Char behavior and properties of reactant mixture interactions (separately and combined)to optimize conditions for syntheses/isolation/purification methodologies (inc reactivity, maintain stability and dec decomp/side products). e.g. cp2mcl2//benz/ water/ benz + water// base// ligand for each and combinations of. Solubility/stability o2-h20/at T=/ any side products/ modified behavior-properties . Cp displacement observed for Cp2Ti(bdt?) and other specific S-S types in presence of excess S-S. Mech? Similar, but not reported for Mo, is formation of CpMo(bdt)2]- or 0. Does displacement depend upon nature of Leq(Cl vs S; does Cp displacement occur more readily in Cl precursor, S-S complex, bdt vs bdtcl2/ vs edt vs mnt / vs qdt etc. metal Ti vs Zr vs Nb vs Mo vs W as function of oxy state/e- occupation/ etc.? *Clearly Cp2M(S-S) are much more prone to Cp displacement than Cl precursors implying stronger donor properties of a donor atom/ligand competes and weakens M-C bonding involving the Cp ring pi orbitals (that strongly interact with the dyz metal orbitals only, resulting in a highly mixed bonding (2b2 Cp based+M and AB (3b2 M based+Cp), 3b2 is at higher energy than 4a1. Donation into 3b2 orbital should lengthen M-C distances opposite the donor group, where in the 3b2 orbital the interaction between the M and these Carbons is AB, thus strong pi donor ligands can compete effectively with the Cp groups for the M d-orbitals and consequently weaken M-Cp bonding.(for comparison see inc Sop-M Charge donation into empty dxzyz AB MO (AB w/r to oxo) that weakens M=O bonding, vs dec charge donation of Sop which inc M=O bonding by inc e- density donated from oxo to metal resulting in M=O length dec/ M-S inc.) Stability of d2 Cp2Mo(IV) bdt is less than Ti d0 analog as evident of disulfide formation on silica gel collumn but much less so on florisil (anaerobic conditions?) Does this mean S-S is easier to be oxidized/dissociated on collumn (silica vs florisil) as opposed to Ti(IV) analog which is stable on silica and in air in solution. Cp2Mo(IV)(S-S) appears to be stable in solid state, but unstable in solution w/r to prolonged exposure to air (O2/H2O?) while the d0 Cp2Ti(IV)S-S is extremely stable in solid/solutions in air or on silicagel etc Anaerobic Reaction of Cp2MoCl2 in solvent(Tol or benz or benz/H2O) + dithiolate salt (Na2(S-S)) or dithiol (H2(S-S))/base (Et3N or NaOH) : T=RT,t=?; T=Rt-70deg, t=?; T = reflux, t=? Solubility/stability/purity profile of precursor (solid/solution sample sensitivity to o2/h20/temp) -What are the extremes in solubility? assume o2/h2o sensitive, use dry-degassed org solvents of various polarity at RT to det solubility properties/then heat in increments above RT to reflux temp (bp) of solvent. Consider the reaction, is it expected to be exothermic or endothermic? Generally expect endothermic thus must put heat in to drive reaction forward; also as Temp increases, the rate of conversion inc (reaction time dec). Thus must heat to sufficient temp such that reaction occurs at a reasonable rate and time to produce high yields without decomposition of reactants and or products. Note that solubility generally inc with temp. The rT range achievable depends upon the bp of the solvent. So choose solvents with sufficient bp that allow temp range for effient conversion at areasonable time without thermal decomposition-side reactions, and that allows for isolation of the product based on sol diffs at a given temp. Generally choose solvent with bp below reactant/product mp (dec decomp) and bp not much greater than h2O as more difficult to handle and more difficult to remove from reaction mixture. Reflux at solvent bp ,choose solvent that is nonreacting/noncoordinating and has the temp that gives good conversion and has desired sol properties for reacting and subsequent separation of target product from mixture, best means as it

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maintains constant temp with constant volume/concentration-dilution that prevents sidereactions based on crowding, or inadvertent crashing out of products or reactants or together upon oversaturation due to solvent loss or temp decrease, also refluxingat bp of solvent restricts decomposition by overheating. -consider solvents of diff polarities that have fp below (how low of temp required to isolate/ppt-recrystall product based on sol diffs at a given temp) and bp less than ~150deg (above becomes more difficult to handle,remove and also less than MP of react/prods to minimize decomp, at higher temps more prone to side reactions/decomposition products, so what is good react temp that gives good yield(minimal decomp) ina reasonable time, and thus what nonreacting solvent allows for the right temp for efficient /fast conversion and provides the right solubility properties w/r to temp range for the reaction and the isolation of desired product from reaction mixture? *take range of solvents dec in polarity : h2O MeCN DCM MeOH EtOH Et2O PETbenz/tol Cyclohexene heptane pentane THF, at RT det what precursor soluble in polar aq or org or NP org, probably sol in most polar solvents purification; -extraction of a substance from suspension or solution in another solvent; separate org substance from inorg impurities by shaking aq solution or suspension with suitable immiscible solvents such as benz,ccl4,chcl3, Et2O, pet, cyclohexane, tol (what is more immiscible with water benz or tol?) meoh immscible with cychexane or PET after several extractions of aq component with immiscible org solvent, combined org phase is dried and solvent evap. See table of immiscible solvents-pairs suitable for extraction -recrystal choose nonreacting solvents of reasonable bp, ease ofremoval after recryst/ more sol at higher temp than it is at rt or below//impurities are either very soluble or only sparingly sol, like dissolves like, if to close sol may be excessive; et2o 34.5 acet 56 chcl3 61 meoh 64.5 thf 64-66 ccl4 77 etoh 78 benz 80 cychexane 81 h2o 100 tol 110 if mat dissolves in cold or with gentle warming solvent unsuitable,as is if it is insol upon heating to bp of solv. If mat dissolves in hot solvent but does not crystalize upon cooling readily within seeral minutes in a ice salt bath try another solvent. Misc solvent pairs; if mat to sol in one solvent and too insol in another for either to be used in recrystal,, it is possible if both are misc to use them as mixed solvent, dissolve in more sol solvent, then the other heated near bp is added to solution untill a slight turbidity persist or crystall begins, add few drops of 1st solvent to clear, and cool to cause crystall. Does strong alkali base result in more readily ox dithiolate leading to disulphides, what is adv of using et3n vs naoh etc. How do you sep or remove ox products, what is best way to purify and maintain purity etc, and remove excess upon completion of reaction Run h2bdt/base vs na2bdt under identical conditions , which is best way; na2bdt vs na2edt is their any diffs with same conditions, what is best yield more reactive/ more stable w/rto oxidation etc/ more stable product Is dithiol or dithiolate salts more stable in solution, more sensitive to air, more soluble in aq or org, more reactive under same conditions, how is salts made more reactive,whichis easier to purify 2.Echem 3d0 Cp2Ti(IV)(S-S) 1 rev red attributed to Ti(IV) to Ti(III) metal centered process/ 2 irrev ox processes. Irrev character of the ox processes is consistent with the electronic structure of complexes possessing a HOMO strongly M-L bonding. (MO picture in conjunction with large folding along S---S hinge in d0 complexes results in distortion of ideal C2v symmetry (fold = 0) for Cp2M(S-S) to Cs symmetry reduction (fold ~40deg, >0-10deg found for d2 complexes which assumed to have C2v), concommitant with better overlap of Sop with dx2 and now symmetry allowed to mix results in a strong interaction stablizing the

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Sop-M MO bonding component which is now the filled S based HOMO S-M b/ destab AB component (Mdx2 –Sop) unfilled M based LUMO? M-S AB. Thus removing e- from HOMO orbital via ox should weaken the M-S dithiolate interaction. note: this assumes dx2 is at higher energy prior to interacting with Sop (but maybe Sop is HOMO for d2, dx2 HOMO-1, where upon ox to d1, large fold occurs that reduces sym/inc overlap so they mix and now each have some ligand or metal character , but still HOMO S based,(now has some Ab char from this interactionHOMO-1 Bchar while before both NB?) that see EPR signal due to the small Metal character mixed in/;note that 95/97Mo a0 small w/r to other complexes where HOMOis mainly metal but highly covalent like Cp2MoCl2. With full ox to d0, removal of e- from AB MO increases the interaction by inc folding to give highly mixed ab now lumo, of considerable M char, with the HOMO-1 now the HOMO with considerable amount of S b character. see below rev red d0 Ti(IV) neutral to d1 Ti(III) paramagnetic anion, add e- to unoccupied LUMO, the AB component to the HOMO? This should weaken this Mx2-Sop interaction and thus dec folding to similar angles found for d1M(IV) paramagnetic neutral complexes(V/Nb) QQ.Does changing e- donor properties of S-S affect red /ox potentials, what about changing metal 3d0 Ti(IV) to 4d0 Zr(IV)? 4d1 Cp2Nb(IV)(S-S) 1 rev red attributed to Nb(IV) to Nb(III) (d1]0 to d2]-/1 rev oxo Nb(IV) to Nb(V) (d1]0 to d0]+ /and irrev ox at more anodic pot. 4d2 Cp2Mo(IV)(S-S) 1 rev red attributed to d2 Mo(IV)]0 tod3 Mo(III)]- HOMO filled, so red involves adding e- to the unoccupied LUMO 2 rev ox: d2 Mo(IV) to d1 Mo(V)]+ to d0Mo(VI)]2+; 1st ox involve removing e- from filled HOMO, so in d1]+ this results in HOMO singly occupied The formulation of the neutral Cp2Mo(bdt) complex as a mononuclear d2 Mo(IV) diamagnetic species with 18e- configuration is consistent with the spectroscopic data. CV experiments performed in DCE (or MeCN) revealed 2 rev ox waves at 0.21 and .615 V vs. SCE() corresonding to the oxidation of the neutral Cp2Mo(bdt) complex to the formally d1 paramagnetic cation and d0 diamagnetic dication species, respectively. The single reversible reduction wave observed at –1.60V vs () was attributed to a metal-centered process, Mo(IV) →Mo(III). Table demonstrates the similar electrochemical behavior of the neutral Cp2Mo(S-S) and Cp2W(S-S) complexes investigated in this study, which can all be formally desribed as M(IV) 18e- d2 species. The measured ox potentials of the Mo complexes are clearly shifted to more neg values, following the expected trends in the e- donor properties of the dithiolene ligands as given here in the order of increasing e- withdrawing ability. A similar trend is found for the W system. However, substitution of W for Mo does not modify the ox pots of these complexes to any significant degree. The smaller values for W and Wbdtcl2 are comparable to the Mo analogs as shown in Table, and this behavior suggests that the HOMO has significant dithilene character 3.Structure/bonding Q.What effects/contributions does the Cp rings have on chemistry/ M-S bonding /geometry/electronic properties of complex in general? and as a function of S-S type and donor abilities, metal (Mo/W) and oxy state change in general and specifically? How does the Cp ring nature, the presence of two rings in bent (vs linear) geometry define the electronic structure of the Cp2M fragment and subsequent bonding interactions geo/electronic structure with coordination of dithiolate? Does the Cp ring and Cp2-M metrics appear invariant for Mo(IV) as S-S changes, oxy state changes , Mo vs W etc. monodentate(H vs Cl vs SR) vs bidentate(S-S, etc) C-CvsC=C degree of saturation? Cp vs Cp*?

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What effects and or defines the extent of bending between the two rings from linear geometry/ and how does the cp ring metric parameters and bending change for given Mand oxy state as function of donor atom type,and or ligand geometry,and or ligand type and nature. What about oxy state changes, and or metal changes? Nature of dithiolate ligand bdt vs edt vs qdt vs dmit, remote effects/e-donor properties/ steric or bulkiness of ligand Q.Does S-S fold affect Cp2 ring bending?Why is there a large diff in s-s fold in our tpmooS-S d1 systems as function of s-s type, yet not correlating with their e-donor properties asdet by echem redox pots?Not much change in d4MoII NO(S-S) as s-s donor ability change, but axial change from oxo to no is big, Oxo-M mo to w not large in our tp d1 +5 systems, e-occupaton effects for 4dMo/5dW 4d2/d1/d0 as oxy state change, for M change and e-occupation but oxy state same M(IV) 3d0Ti 4d0 Zr/ 3d1 V 4d1Nb/ 4d2Mo 5d2W e.g. Cp2Mo/W Cp2MH2,Cl22,SH2,SR2,bdt,bdtcl2,tdt,edt,qdt,dmit etc Cp2MCl2 dmit,SR, bdt,d2/d1/d0, what is origin of distortion of s-s from zero in d2 systems?crystal or electronic: steric effects –bulkiness of s-s ligand, nb interactions with Cp, e-donor properties of s-s, energy of M and L frontier orbitals,sym of M-Lfrontier orbs,other struct distortins, e-occupation for given oxy state diff met, e-occ for oxy state change for given M. Derive MO diagram including Metal (M=G6:4dMo/5dW; d2IV/d1V/d0VI; G4 3d0Ti(IV) 4d0 Zr(IV)/G5 4d1 Nb(IV)) and ligand (Cp/2Cp; S-S/S-S =bdt,bdtcl2,bdtme; edt; qdt; dmit)contributions independently and acting in concert. Cp2Moedt vs Cp2Mobdt; edt vs bdt ; nature/type of dithiolene on geo/elec structure and contributions to reactivity. -edt is a true ene-1,2-dithiolate while bdt is approximated as one, it is an aromatic 1,2-dithiolate; also edt is the simplest ene-1,2-dithiolate possible and should simplyfy the electronic spectral interpretation vs bdt (more orbitalsetc) and makes it a more tractable computational DFT and GT problem; further edt will not have the added complexity of remote ligand effects ancillary to s-c=c-s ring, thus isolates this ring and its contributions . also not expect steric bulkines to be factor here in edt. How similar/diff is geo-electronicstructure in iso system diff only in the type of s-s (edt vs bdt vs qdt etc). What is known in lit for isostructural/isoelectronic TM-mono/bis/tris/ edt-bdt complexes(reffs)?in particular For isostructural M=Mo/W +4d2/+5d1/+6d0 complexes(refs)? Regarding ligand properties and trends free ligand and complexed ligand, effects on chemistry and geo/elec structures of analogous complexes. How diff are metrics echem electronic spectra etc. 1.holms monooxo bis s-s Mo/W +6//desoxo+4 bdt vs edt 2.holms dioxo mono (s-s) Mo +6// monooxo mono-s-s Mo +5 bdt vs edt 3.mono oxo bis s-s Mo/W +5/+4 bdt vs edt 4.Tp*MoO(S-S) +5 now availlable 5.Cp2Mo/W (S-S) +4 bdt vs edt now more availlable// other TM G4/5 6.CpM(s-s)2 +4/+5 very little 7. M(s-s)3 +4/5/6 bdt vs edt 8. other TM (s-s) bdt vs edt analogs (e.g. Ni/Pt etc 9. remote substit effects electronic and geo/steric on edt H vs,CH3,CF3, CN, PH, PHcl etc, how diff is this w/r to remote sub effects on bdt 10 deg of sat c=c edt vs c-c EDT. Structure for Mo(V)Oedt2 EDT2.electronically/geo what can we derive from our Tp*MoOs-s and Cp2Mos-s systems Exp: 1. Char free Na2(s-s)/(s-s)2- ligands bdt and edt, and EDT w/r to their geo/electronic/echem/chemical properties and stab/reactivity;

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Det purity(any impurities HNMR/ can we tell if disulfide oxidation products-how do we separate) how sensitive is ligands w/r to o2/ what about water? Are the salts and dithiols sol in aq? What org solvs? From synth of ligands and subsequent purification by extract/recryst of na salts which can be protonated and fract dist nunder vac what doexpect each to be sol in and how sensitive to o2, how can remove ox decomp products such as disulfides, how does base et3n vs naoh affect h2s-s, its decomp in presence of air and base, the cleavage of disulfide bonds by alkaline base . 1H-NMR and 13C-NMR// MS ESI? In MeOH//IR-UV-VIS// echem(H2tdt been done)/gasphasePES HeI/II of Na2(S-S) forms(H2bdt beendone)? Dft calcs of H2(S-S)/Na2(s-s)/S-S 2- (huckel of bdt2-/bdt0)// GT treatment of bdt vs edt dianion ligands MO/vib/electronic -GT treatment of edt vs bdt, fragment analysis c=c vs benz ring MO more MOs (pi, sig) in benz ring more complicated system, also sig orbitals B/AB overlap with Pi,diff nodal behavior, then let S valence orbs interact in c2v. Huckel vs dft see structures and electronic properties of c=c/benz ring and subsequent dithiolate derivitives. H2C=CH2 D2h HSC(H)=C(H)SH c2v –SCH=CHS- c2v c6h6 d6h S-C interactions in BDT vs edt result in different splittings, sop in particular due to diff nodal behavior, sop sym vs sop asym, what are vie of these before interacting with M, are they ~isoenergetic destab/the other stabsome what with Cp2M fragment homo, is the destab of one of the sop due to interaction with a benz ring orbital What about bdt vs bdtcl2/tdt vs qdt vs edt (vs EDT) -Gt treatment of Cp rings/ Cp2M fragment linear to bent any calcs see structures and electronic properties of fragments and of Cp2Mo/ H2 /etc. A general synthetic route established for the preparation of mononuclear Mo ene-1,2-dithiolate comlexes and other related high-valent TM dithiolene systems involves reactions of the appropriate metal halides suspended in an organic solvent with 1,2-dithiol proligands in the presence of a strong base or directly with preformed salts of 1,2-enedithiolates.

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OLIS OPERATIONS 1.Turn on power grid for all on power strip. 2.Make sure not to bother toggle switch on front panel, it is always left on. 3.If Deuterium lamp is not lit play with plug untill it does, this needs to be replaced. 4. Enter OLIS at prompt, the hit enter for directory Rachel, It will ask you to enter slit width (enter zero if it was closed right to begin with, this dial has gotten out of wack and needs to be readjusted. Enter wavelength as read on dial, e.g. 250 nm. Once in front main menu, hit S for scan data collection. Note in this menu is where one can change the lamp and detector changeover. You are in an ABS exp mode. 5.set up your scan wavelength range,say 900 to 300nm and run. Then can repeat with cell and solvent, save as baseline which will auto subtract out from sample runs. Now run the sample. Make sure you save the data to hard disk before exiting program or you will lose the data. 6. note if you use the NR IR detector i.e 901-2800nm, you will need to make sure bar is pushed in all the way. When detector change over occurs, say at 840 (900-700), scan will stop and ask you to change; just pull out gently and make sure don’t get a large jump. 7.When you are finished, make sure you exit correctly, and control Z to close the slits to zero. Note that I will before running experiment close the slits to zero so I know where they are. Donot just turn off or exit program without doing this. You will see this exit command in menu. 8.Make sure cells are clean after using.

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Here are some points I had put forth to hemant to continue studies on. Goal Probe the electronic structure of mono oxo molybdenum mono ene-dithiolate. Determining key factors (geometric and electronic factors) that contribute to the electronic

structure, and hence redox potentials. Determining the origin of the electronic structure differences in the (Tp*)MoO(S-S) series of the compounds in a controlled six-coordinate environment.

Compounds (Tp*)MoO(S-S), S-S = bdt, tdt, bdtCl2, qdt New Target Compounds (Tp*)MoO(S-S), S-S = edt, edtMe2, mnt, (Tp*)MoO(S-S), S-S = bdtCl4, bdtMe4, 4,5-bdtMe2, 4,5-bdtCl2, bdt(OMe)1,2 (Tp*)MoO(S-S), S-S = qdtCl2, qdt(OMe)2, qdtMe2 (Tp*)MoO(s-s) = EDT, EDTMe2, PDT (saturated) (Tp*)MoO(O-O) O-O = bdo, qdo (Tp*)MoO(S,S) = SPh Outstanding issues to be addressed for models A. Three ene-dithiolates (edt, bdt, qdt) 1. Benzene ring derivatives: remote ligand and second coordination effects. a. Substantial redox potentials and first ionization energy shifts. However, remote ligand effects on the benzene ring donot perturb the electronic structure as great as qdt. For example spectroscopic properties such as Elec. Abs., MCD, rR, IR, EPR are not greatly different. b.We have observed a second coordination effect regarding fold angle that may contribute to the electronic structure by effecting the orientation of the orbitals involved in the metal-sulfur interactions and charge donation c. The question is what the electronic structure differences due to ? Zeff of sulfurs/metal : remote ligand donor effects. Second coordination effects: Fold angle, M-S-C angle.

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2. Qdt: We observe significant shifts in all electronic properties. Unlike above compounds we observe significant changes in the spectroscopic features, which we have attributed to differences in the out of plane sulfur donor properties (Anisotropic bonding) w/r to bdt. However, even though the inner coordination sphere appears to be invariant suggesting that the electronic differences are due to the effective nuclear charge of sulfurs. We have also observed a second coordination effect regarding fold angle that may contribute to the electronic structure by effecting the orientation of the orbitals involved in the metal-sulfur interactions and charge donation (see above bdt) B. Saturated dithiolates (EDT) Orbital rotation effects of a bi-dentate dithiolates. EDT: C-C vs. edt: C=C. Chelate ring size/ flexibility EDT vs PDT. C. Bis-thiolates (Sph) Orbital rotation effects of a monodentate thiolate. D. Different equatorial donors (BDO)