Investigations of Metal Carbonyl Complexes

as Potential Catalysts for the Alternating

Co-Polymerization of Imine and CO into Polypeptides

A thesis submitted to the Faculty of Graduate Studies and Research

in partial fulfilment of the requirernents of the degree of Master of Science

by Danny Lafiance

Department of Chemistq McGill University, Montreal

March 1999

O Danny Lafrance 1999

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ABSTRACT

The objective of this study is to investigaîe the potential use of transition metai carbonyl complexes for the sequential insertion of CO and imines, with the ultimate goal of

developing an imine/CO CO-po1ymeriZation catalyst.

The reactiviîy of (CO),CoMe with Tol(H)C=NMe has been investigated and evidence of imine insertion into the Corn-acyl bond of (CO),Co(COMe) is observed by 'H- NMR. Atîempts to generate the postulated product of Tol(H)C=NMe insertion into

(CO),Co(COMe) by addition of (CO),Coe to Tol(H)CN(Me)COPh+Cl- led to

decomposition.

The reaction of (CO),MnR (R = Me, Ph) with imines Tol(H)C=NR' (R' = Me, Bz, Ph) yielded ortho-metallated products (CO),Mn[2,5-C,H,(CH=NR') (CH3)]. The r d o n of (CO),MnMe, Tol(H)C=NMe, and AlCl,, afford (CO)4M.n~H(Tol)N(Me)C(0)Me] (51). Attempts to generate a CO/miine insertion product by the addition of to

Tol(H)CN(Me)COPh+Cl- yielded the new complex (CO),Mn(C(O)CHflol)N(Me)C(O)Ph] (54), incorporating an uiserted CO into the Mn-R bond. The x-ray crystal structure of (54),

and (PPh,)(CO),Mn[CH(Tol)N(Me)C(O)Ph] (61) were obtained and are discussed.

L'objectif de cette recherche est l'étude des carbonyles de métaux de transition (CO)$R pour l'insertion séquentielle d'imindC0, dans le but de developper un catalyseur pour la copolyrnérisation dlimine/CO.

La réaLwté de (CO),CoMe et Tol(H)C=NMe a été etudiée et des évidences d'insertion d'imine ont &é observée par RMN. Les tentatives pour genérer le produit d'insertion de Tol(H)C=NMe dans (CO)4Co(COMe) par addition de (CO)4Co et TO~(E~~CX~VIC)C]S?!I+C~,- conduisent à la décomposition.

La M o n de (R = Me, Ph) avec les irnines TolOC=NR' (R' = Me, B Z, Ph) génère (CO),Mn[2,5-C& (CH=NR')(CH3)]. La réaction de (CO),MnMe, Tol(H)C=NMe et Alci, genere le nouveau produit d'insertion d'imine (CO)4Mn[CH(T~1)N(Me)C(0)Me] (54). Les tentatives pour gknerer un produit d'insertion imindC0 par addition de (CO)&h- et Tol(H)CN(Me)COPh+Cl- donnent le complexe (CO),Mn[C(O)CH(Tol)N(Me)C(O)Ph] (54), avec un CO insért5 dans le lien Mn-R Les structures rayon-x de 54 et 61 ont été obtenue et sont discutée,

ACRNOWLEDGEMENTS

First, 1 would Like to express rny gratitude to my Supervisor, Dr, Bruce Amdtsen, for guidance and encouragement throughout the span of this work and the precious help for the WTiting of this thesis. Dr. Amdtsen7s cornmitment and constant strive for excellence have always been a source of motivation,

&O, the long and often tieng hours in the lab 443 wouldn't have k e n the same without fiiendship of some people: NgiapKie Lim and Rania Dghaym, who have been there fiom the beginning, Jason Davis and David Llewellyn (who proof-read this thesis, thanks), as weU as Andrew Oliver, Jean Lao and Annie Ferrary. 1 am also thankfüil to the former members of the group: Virginie Guillemette, Dan Adamson, Valerie Paquette and Karin Yaccato- To a l l of you: "The best of luck!"

Je voudrais aussi remercier Dr- Anne-Marie Lebuis et Dr. Céline Pearson pour la

crystallographie par rayons-x, de même que Dr. Jacques Turcotte et Dr. Bruce Lennox pour leur soutien. À Renée Charron, ma plus sincère gratitude pour votre aide si appréciée.

Un bon mot aussi pour Dr. Davit agarian et son groupe de recherche, et pour la "gang" de fou qui ont maintenu mon moral a flot: rnaîae Aubin, Jeff et Nadia, big Louke, le druide rnéïomane, Hugo le germanique, Sophie, les sympathique Bleu-Blanc-Rouge Luc et Caroline, de même que tous les "Anglos" que j'ai eu la chance de connaîî pendant les deux denii&res années.

1 wouid like to ackowledge the financial support of FCAR, as well as NSERC, ESTAC, and McGill University through the Max Stem Recruitment award-

Je voudrais dédier cette thèse à mes parents, mes et Yolande. Merci pour votre support.

"Un dîplome en chimie organom~talliqye représente l'incarnation contemporaine du Mythe de Sisyphe -2 DL, 1999

TABLE OF CONTENTS

Chapter 1: Introduction to the metal catalyzed alternating CO-polymerization of CO and unsaturated monomers

.................................................................................... 1.0 Perspective 1

Co-polymerization of o l e h and CO: Synthetic routes to poly-ketones ................ 4

................................................................................ 1.1.1 History 4

1.1.2 Mechanism of the metal catalyzed COfolefin CO-polymerization ......titi...... -6 1.1.2.1 The perfectly altemathg oleWCO CO-polymerization structure ... 6 1.1.2.2 Mechanistic mode1 for CO-polymer chain growth .................... 8

1.1.3 Scope of metal catalyst for olefin/CO CO-polymerization ....................... 9 .................. . ...... 1 1. 4 Olefin monomers for olefin/CO co.polymerization .. .. 11

1.1.5 Enantioselectivlty in the altemating CO-polymerization of olennS and CO .. 11 ............................................................. 1.1.5.1 Introduction I l

.................................... 1.1.5.2 Enantioselective copolymerization 13

.............................................................. IminelCO co.polymerization 16 ......................................................................... 1.2.1 Introduction 16

................................................... 1.2.2 ConventionaI peptide s ynthesis 16

1.2.3 A potential imine/CO CO-polymerization route to polypeptides .............. 18 ............................................................. 1.2.3.1 Introduction 18

1.2.3.2 Postulated imine insertion with CH$ O (CO), ...................... 21

1.2.3.3 Postulated imine insertion with Fe2(CO),(R .DAB) ................ 22

1.2.3.4 Postulated imine insertion with tricarbonyl (vinylketone) Iron .......................................................... (0) complexes 24

1 . 3 The altemating insertion of CO and imine into a Pd.CH, bond ....................... 25

................................................................... ......... ...... References ... .... 29

. . 3.4.1.1 Reactlvlty ........................................................ -76

........... ................ 3.4.1.2 Reactivity of 60 with PPh , .... 77 3.4.1.3 X-ray structural data for 61 ................ .... .......... 77

....................................... 3.4.1.4 Reactivity of 60 with CO 79 3.4.2 Reactions of 54 with triphenylphosphine ........... .... .................. 79

3.4.3 Reactivity of 54 with Tol(H)C=NCH, .......................................... 82

3.4.3.1 Reaction of 54 with Tol(H)C=NCH, ......................... 82

............. 3.4.3.2 Reactions of 54 and Tol(H)C=NMe with AlCl, 83

A) Reaction of 54 and Tol(H)C=NMe with AKl, ................ -83 B) Reactivity of complex 64 .......... ,. ................................ 84

................................................ 3.5 ImineKO CO-polymerization experïments 84 .......................................................................... 3.5.1 Objectives -84

3.5.2 Reaction of (CO),Mn -Me with Tol(H)C=NMe ................................ 85 3.5.3 Reaction of (CO),Mn -Me with Tol(H)C=NMe in presence of AQ ........ 85

.......................................................................... 3.5.4 Conclusion 86

......................................................................... 3.6 General conclusion 86

........................................................................................ References ..89

........................................................................... Experimental section -93 ................................................................................... LGeneral 93

2.General procedure for the high-pressure CO reactions .......... .... .......... 94

3.General procedure for NMR experiements ........................................... 94

4.Experimental details ..................................................................... 94 References ............................................................................... 103

LIST OF FIGURES

........................................... Fig . 1 Photodegradation of ethylenelC0 CO-polymers 2

Fig . 2 Denvatization of ethylenefC0 CO-polymers ............................................... 2

Fig . 3 Bidentate nitrogen ligands in P d 0 catalyst of the type (N-N)PdR(L) for . . ............................................................... olefidCO CO-polymenzation 10

Fig . 4 Stereospecific configurations for tertiary carbon of polypropylene ................... 11

Fig . 5 Stereogenic centre of an olefin/CO CO-polymer ......................................... 12

Fig . 6 13c-~MR spectra of the methyl group region for PIC0 c o - p ~ l ~ m e r ' ~ ............... 14

Fig . 7 RSR triad of olefin/CO CO-polymer ....................................................... 14

Fig . 8 13c-NM~ spectra in the region of the C(2) resonance of poly-

............................................ (4-tert-butylstyrene-alt- carbon monoxide)17 15

Fig . 9 Transition state for acyl insertion ...................................................... 15

Fig . 10 Thermodynamics of oleWC0 and imine/CO CO-polymerization reactions ......... 37

Fig . 11 a@) and n-bondhg mode O of an imine to a transition metal . Example

............................................................ of a x-bonded imine (26)" 24

Fig . 12 Molecular structure of 34b . Selected bond lengths (A) are as foUows:

Pd.O(l). 2.008(6); Pd.C(l2). 2.022(8); 0(1).C(13). 1.265(10); N(3).C(13). 1.328(1 1); N(3 jC(12); 1.498(10) ........... .... ................................... 2'7

Fig . 13 General structure of ortho-manganated species ..................................... 3 8

Fig . 14 Stereochemical differentiation of axial CO ligand for 54 ............................ 70

Fig . 15 Low temperature 'H-NMR specaa (4-6 ppm) of complex 54 formation .......... 71

................. ............ . .... Fig 16 X-ray crystal structure of complex 54 ... ...... 73

Fig . 17 Se1ected bond lengths (A) for complex 54 six membered ring and the .......................... ............. reference molecule formamide (59) " .... -74

Fig . 18 X-ray crystal structure of 61 .................... ...... ............................ -78

Fig . 19 NMR specaoscopic data for 62 ......................................................... 80

LIST OF SCHEMES

Scheme 1-

Scheme 2.

Scheme 3 .

Scheme 4 .

Scheme 5 .

Scheme 6 .

Sheme 7 .

Scheme 8 .

Scheme 9.

Scheme 10 .

Scheme 11 .

Scheme 12 .

Scheme 13 .

Scheme 14 .

Proposed mechanism for alternaîe insertion of GH4 and CO into ...................................... ............................ a Pd-R bond ... 5

Equilibrium between the carbonyl(4) and o l e h (5) coordination complexes of [(Phen)PdCIE,CEE,C(0)R]+Af4 B. and the corresponding rate of insertion into Pd-R bond ........................................................ 6

Complete mechanistic cycle of chain propagation for the

CO-polymerization of ethylene with c09 .......................................... 8

................................................... Solution s ynthesis of Gly.Ala 1 7

.................................... .......... Merrifield Peptide S ynthesis ...,. 18

Amide synthesis mediated by cobalt carbonyl complexes ..................... 21

Postulated mechanism of amide formation ...................................... 21

Postulated imine insertion into an Fe-acyl bond ................................ 23

Postulated mechanism of amide formation ...................................... 35

Preparation of NaCo(CO).(PPh. ) .... .... .................................. 47

Dialkylketone formation from alkyl tetracarbonyl ............ ....... ...... ..... 48

Postulated decomposition mode for (CO)4CH(Tol)N(Me)(COMe) .......... 49

Sequential insertion of CO and dicyclopentadiene into Mn-R bond of the complexe (CO)5 MnR @=Me. Ph) ................................. 53

E-enone (l), butenolides (2), and ketones (3) synthesis

............................................... using manganocycle intermediate' 54

..................... Scheme 15 . Proposed mechanism for azobenzene orthomanganation 59

Scheme 16 . Two possible mechanisms of ortho-metallation of ................................................ Tol(H)C=NR' with (CO),MnMe -60

Scheme 17 . Reaction of Lewis bases with methylmangame pentacarbonyl ............. 61

Scheme 18 . Alkyl migration mediated by molecular Lewis acid AICI ,... .................. 62

Scheme 19 . Postulated role of AlCl. in imine insertion .................................... -65

.... . ............................. Scheme 20 S ynthesis of 54 and reactivity with PPh3 ,.... -88

LIST OF TABLES

Table 1 . Conversion of (Arr)(ACO)C=NR to 22 at 60°C .............................. 22

Table 2. Imine binding constants for 32a-d .............................................. 25

...... Table 3 . Bond lengths (A) of backbone metallocycle for complex 61 and 34b 78

CHAPTER ONE: INTRODUCTION TO THE METAL CATALYZED ALTERNATING CO-POLYMERIZATION OF CO AND UNS ATURATED MONOMERS

1.0 PERSPECTIVE

The insertion of unsaturateci substrates into transition metalcarbon bonds is a key step in many important catalytic transformations mediated by transition metal catalysd2 This is particularly me for polymenZation processes, where poly-insertions of carbon- carbon multiple bonds leads to polymeric matenalS. Since the discovery of the Ziegler-Natta polymerization in the early hfties, impressive progress has been realized in this field.) Today, homogeneous olefin polymerization by means of group 4 mernocene systems is undoubtedly the most versatile route to poly-olehns with controlled stmctures and molecular weightd

Despite the considerable volume of research on the polymeBzation of unsaturateci substrates catalyzed by transition met&, the insertion monomers studied have been mainly

restricted to simple a-olefins to generate poly-olehs. The introduction of functionality into

the backbone of insertion polymer has ben a much more recent developrnent, and has evolved an intense field of research? Perhaps the most significant area of study in this field has been the CO-poïymerization of carbon monoxide with olefins using organometallic cataiysts to generate poly-ketones (eq. 1- 1).6

(eq. 1-1)

As with poly-olefins, poly-ketones can be prepared fiom available and inexpensive

monomers, and their macroscopic physical properties can be varied with the a-olefins

employed, In addition, poly-ketones have several usefd properties that are distinct fiom simple poly-oIefbs- The presence of reactive carbonyl groups in the polymer backbone confer grea;ter photodegradabiky to the co-polymer when compared to the corresponding poly-oleiins. GuiUet and CO-workers have shown that light absorption in the near W-

region by the copolymer resulted in a decrease in polymer molecular weighf accompanied by the evolution of ~ 0 . ~ ~ TWO different decomposition modes have even been postuiated mg. 1). The type 2 reaction was found to be predominant at room temperature, while type 1 is favoured at higher temperanires. Furthemore, the general rate of CO-polymer degradation was found to decrease with tùne, due to formation of funaional groups that do not participate in type I or type 2 reactions.

Type 2

In addition to their degradability, o leWC0 CO-polymers can be readiiy chemically modified at the carbonyL6 Since poly-ketones behave like typicai ketones in the reaction they undergo, they can be used as potential starting matenals for the synthesis of other classes of functionalized polymers. Brubaker and ~offmar? have reported several examples of this chemistry, as presented in Figure 2.

HCN PH - KCN -(CH2CH2-ç-)-

CN

Fig. 2 Derivatization of ethylene/CO CO-polymers

Introduction of functionality into the polymer backbone c m also be achieved by

modifying the olennic monomerics uoits. In a recent study, Novak reported3' the alternathg CO-polymerization of e1stron-poor bicyclic olefin 1 with CO using neutral palladium (II) alkyl complexes (Eq. 1-2).

- X=Q Br, 1

poly (142 -CO)

In this example, the monometic units 1 were used as a 'protecting group" for latent polymeric double bonds. Upon heating, poly(1-&-CO) undergoes a retro Diels-Alder reaction, to produce furan derivatives and a new cross-conjugated material poly(ketoniny1ene) (PKV) (Eq. 1-3). The furan solvent formed duÔng the conversion acts as a solventfplasticizer for the mutating polymer, allowing the formation of continuous, defect-free PKV Wms.

retro Diels-Alder 0 n (Eq. 1-3)

PKV

The synthesis of poly-ketones via the aitemathg CO-polymerization of olefins and CO has been extensively investigatecl over the past 20 years. A brief review of the work done in thaî field is presented in the next section

1.1 CO-POLYMERIZATION OF OLEFINS AND CO: SYNTHETIC ROUTES TO POLY-KETONES 1.11 HISTORY

The fkst example of the CO-polymerization of olefins with CO (1950) was described in a patent by ~rubaker? It consisted of a fk radical initiated CO-polymerization of CO and C2H4 under high gas pressures (up to 1 0 Mpa) and reaction temperatures (120-165°C) (Eq. 1-4). Poly-ketones with molecular weights up to 8000 were obtained. Interestingly, the percentage of CO in the CO-polymer was found to Vary, and depended upon a variety of different factors, including temperature, pressure and gas composition. Almost 50 mol!% incorporation of CO in the CO-polymer was achieved by using a monomer mixture

of > 70 mol% CO. In a related work, y-ray were also found to induce the CO-polymerïzation

of CO with C2H4, presumably resulting fiom the capacity of y-radiation to induce fie

radical fonnation6

"radical initiator"

The fint example of transition metal complexes capable of catalyzing the co- polymerization of CO and olefins was descn'bed in the 1970s in a patent by ent ton.^ The

researchers u-d Group 10 metal d y s t to co-polymerize CO and ethylene. In contrast to the radical polymerizattions, this system yielded a high melting solid polymer with a regular structure of altemahg CO and C F 4 mits (Eq. 1-5). The catalysts patented inc~uded:~ Pd(CN),, HPd(CN),, PdCYPR, and Pd(PPh,),. However, similar to radical induced CO-polymerization, these systems required relatively high temperatures (100-140°C) and a combineci gas pressure varying fkom 5.5 to 12.4 Mpa. No mechanistic information was available concerning these metal catalyzeü CO-polymerizations.

In 1982, Sen reported7 that the series of cationic palladium 0 compounds

Bd(CH3CN),(BFJ2-nPPhJ (n=1-3) (2) catalyzed the perfixtly altemating CO-

polymerization of carbon monoxide with a range of olefuis under unusually mild conditions. For instance, high molecular weight altemating ethylenecarbon monoxide CO-

polymers were fomed by the reactions of 2 with a mixture of CO (350 psi) and C2H4 (350

psi) at 25 OC for 1 day (Eq- 1-6).

Sen proposed a m e c m m involving the alternate insertion of CO and C2H4 into a preformed Pd-alkyl bond (Scheme 1). This hypothesis was supported by the fact that the

species generated by feactiom of AgBF, with (PPh3)PdMeI (3) (Le. (PPh,),PdMe+) was also an active catdyst for the CO-polymerization reactions. Sen also demonstrated tfiar neutral species like 3 and (PPh,)J?dCL, were completely inactive under the same reaction conditions, thus indicating the crucial need for an w î l y accessible coordination site on Pd, and an &y1 ligand into which CO and olefin can insert,

Scheme 1 Proposed mechanism for alternate insertion of C2H2 and CO into a Pd-R bond

1.1.2 MECHANISM OF THE METAL CATALYZED CO/OLEFIN CO-

POLYMERIZATION Several studiess covering the mechaniSm of palladium catalyzed o1eWCO co-

polymerization have been published over the past 10 years. The most detatled and complete investigation available, covering the kinetics and thermodynamics of the reaction, was done

by Brookhart and CO-wodcers in 1996.' The important features of the mechanism are summarized below.

1.1.2.1 THE PEREECTLY ALTERNATING OLEFINICO POLYMER STRUCTURE

sen7*" first proposed a mechankm involving the altemathg insertion of CO and

C a into a Pd-allcyl bond. In order to get an alternathg structure, th& mechanism necessarily q u i r e s the preferential insertion of CO into a Pd-alel bond, and the

preferential insertion of olefïn into the Pd-acyl (ie. Pd-COR) bond. To investigate the

reasons why CO insertion into a Pd-alkyl bond was preferred over the corresponding insertion of C2H4, ~ r o o k h a d examinai the equilibnum between Pd-carbonyl 4 and Pd- olenn 5 complexes (Scheme 2).

Scheme 2 EquiliMum between the carbonyl(4) anà olefh (5) coordination complexes of [(phen)PdCH~2C(0)Rl+Arf4B4B and the corresponding rate of insertion into the Pd-R bond

It was found that the equrlibrium Iay far to the side of the carbonyl complex 4, with

a ratio of approximately 104/1 for carbonyl(4)/olefin(5) complexes. Furthemore, Brooktiart showed that the rate of migratory insertion of CO into a Pd-alkyl bond &,)

relative to ethylene insertion into a Pd-alkyl bond (k3 wax k,-dk, = 2000/1. Combining these two effects, the preferential binding of CO and its faster rate of insertion, the

probability of 2 consecutive ethylene insertions are thus expected to occur roughly 1/10"

times.

On the other hand, Sen has demonstrated" that CO insertion into a Pd-acyl bond, to give the double carbonyIation product, is a themodynafnically unfavourable process for P d 0 complexes. The mode1 compound PdCOCOPh(Cl)(PPhJ, 6, prepared b y oxidative addition of PhCOCOCl to Pd(PPh,),, was shown to undergo rapid decarbonylation at room temperature (Eq. 1-7). The rate of decarbonylation was found to be unaffectecl by the

presence of up to 700 psi CO. Similarly, no trace of the double carbonylation product was observed when the acyl complex 7 was exposed to 1OOO psi of CO at r.t (Eq. 1-8). These results suggest that the equilibrium constant for Eq.1-8 is extremely mail at room temperature, thus preventhg double carbonylation product to fom.

Taken tûgether, these results show h t CO insertion into a Pd-alkyl bond is kinetiçally favoured over olefin insertion, while CO insertion into a Pd-acyl bond is therxnodynamically uphill, thereby allowing the slower olefb insertion to occur. These two ensure the altemating CO-polymer structure.

1-1.2-2 MECEUNISTIC MODELS FOR CO-POLYMER CHAIN GROWTH Using kinetic and thermodynamic data for the model complexes (phen)Pd(R)(L)

(R = CH,, CH,CH3, C(0)CH3, C&C&C(O)CH,, C(0)CHQ3$(O)CH3, L = CO, WJ, Brookhart postulatedg a mechanistic model for CO-polymer chain growth that closely matches the experimental turnover fkquency for ethylenelCO CO-polymerization. The complete model is presented in Scheme 3.

Scheme 3. Complete mechanistic cycle of chah propagation for the CO-polymexïzation of ethylene with C e

P = P01y(C2&-alt- CO) h '+

resting state

First, in agreement with the fast rate of CO insertion into a Pd-alkyl bond, and the preferential binding of a carbonyl ligand to Pd over an olefîn, the r e g state of the caîalytic cycle has been found to be the complex 8. This complex must then overcome a

large kinetic banier to form the ethylene acyl complex (9) which undergoes kacyl

migration in the tunover Limiting step. Subsequent formation of complex 10, foiiowed by a fast CO insertion and trapping by another molecule of CO, reforms the iesting state 8. It should also be noted that within the catalytic cycle, formation of the a m 1 carbonyl complex 10 is favoured over the olefin complex l2, represented by the low equilibrium constant K, = (9.9 f 5 ) x 10% This s u m m m the mechanistic aspect of the olefidC0 copolymerization system,

1.1.3 SCOPE OF METAL CATALYST FOR OLEFIN/CO CO-

f OLYMERIZATION

Following Sen's report using [Pd(CEf,CH),(BF,)pnPPhJ (n=1-3) to catalyze

oiefWC0 CO-polymerization, the development of similar Pd@) catal.yst has received considerable attention. ~ n e z e ~ ~ and Drent? simultaneously reported that the use of bidentate phosphine ligands on palladium acyl complexes (13) yields catalyst which CO-polymerize olefins and CO to produce high-molecuïar weight poly-ketones with signifïcant conversion rates.

P-P = diphenylphosphinoethane (dppe) diphenylphosphinopropoane (dppp) diphenylphosphinobutane (dppb)

Subsequently, similnr palladium complexes with bidentate nitrogen ligands, e . g . N-W p-tetramethylethylenediamine (tmeda) 14, 38 bipyridine (bip y) 1 5, 3g*39

phenanthroline (phen) 16" and bis(aryIimino)acenaphthenes (BIAN) 17~' were also shown to be active cataiysts for oleWCO CO-polyme&ation (Fig- 3)- The high activity of

these bidentate ligand complexes likely atises from the required orientation of the empty Pd coordination site ch to the alkyl acyl ligand, thereby accelerating migratory insertion.

Fig. 3 Bidemate nitrogen ligands in P d 0 catalyst of the type (N-N)PdR(L) for olenn/CO CO-po1ymexizat.m

In addition to palladium catalysts, a number of other metal systems have been found to catalyze oleWCO CO-polymerization. For example, rhodium complexes of the type

RIiA(CO),(PPh,),, (x = 0-3) were found to co-oligomerize o l e h and carbon monoxide." Yamamoto also reponed re~ently"~ that RbH(PPh,), catalyses the living CO-polymerization of axylallenes 18 with carbon monoxide to give structuraily regulated polyketones (Eq. 1-9).

18

Ar' = W O M e - p

Nickel complexes capable of CO/olenn altemathg CO-polymerization have also been reportedM and theoretical study even suggest that Ni-based catalyst are more reactive then their Pd analogues ?' However, these catalysts have not been investigated in as much de- as their Pd anaiogues, and the mechanism of their actïvity is not fully understood.

1.1.4 OLEFIN MONOMERS FOR OLEFINKO CO-POLYMERIZATION Although there has been simiiflcant progress made in the area of metal-catalyzed

oleWCO co-polyrnerization, only limited classes of olefin have been shown to be active in

this process: ethylene, propylene, styrene and strained cyclic olefins (e-g. norbomene)." More stericaïIy uncumbered olefïm, such as 3,3-diethyl- 1 -butene, vinyltrimethylsrlane, as well as electcon-poor substrates such as methylvinyl ketone, methyl acrylate and diethyl maleate, failed to afford co-polymers with the Pd systems investigated?

1.1.5 ENANTIOSELECTlVITY IN TEl3 ALTERNATING CO- POLYMERIZATION OF OLErnS AND CO

Recently, there has been increasing interest in the altemathg co-polymerization of

a-olehns with carbon monoxide catalyzeü by chiral transition metal c o r n p l e ~ e s . ~ ~ ~ ~ ~ A

concise review of this growing field is presented in the foiIowing section.

115.1 Introduction The physical behaviour of a polymer depends not only on its general chemical

composition, but ais0 on the more subtle differences in rni~rostructure.'~ From a pracrical standpoint, the interest in polymers with controiïed tacticity is denved fiom their superior mechanical propertîes, higher crystaïlinity, and higher melting points when compared to the

corresponding atactic analog~es-'~ Highly stereoregular isotactic poly-a-olefïns have been

prepared using chiral homogeneous transition metal ~a t a ly s t s .~ These polymers do not show optical activity because the tertiary carbon is only pseudo-asymmetnc, king centrosymmetric relative to the main chain, where the two polymer branches are more alike for long poIymers (Fig. 4).

Fig. 4 Stereospeciîïc configurations for tertiary carbon of polypropyiene

In contrat, regiospecinc CO-polymers of a -o l ehs and carbon monoxide contain

tme stereospecific centres dong the polymer backbone (Fig. 5), and are optically active polymers with mainchain chiraLity. An absolute configuration can then be assigned, using the Cab-Ingold-Prelog system, referring to the R-(rectxis) or the S-(sinister) form

"R" "S"

Fig. 5 Stereogenic center of an olefin/CO CO-polymer

Polymers of this type can be grouped into 3 general classes of ta~ticity,'~ depending upon the distribution of the chiral centres within the chain:

Isotactic: When ail the stereogenic centres of an oleWCO copolymer have the same

absolute configuration, e.g, (SSSSS) or (RRRRR).

Syndiotactic: When the absolute configuration of stereogenic cenues of an olefïn/CO copolymer altemte , e.g.(RSRSRS)

Atactic: When the stereogenic centres of an oleWCO copolymer are randomly distributexi dong the chain, e.g. (RSRRSR)

Since the mechmical properties of a -o leWCO co-polymers can be significautly

altered due to the relative chirality of neighbouring sites (similar to diastereorners), the

synthesis of a-oIeWCO copolymers with controlled tacticity is an intense a r a of research.

A bnef summary of recent advances realized in this field is presented in the following section,

1.1.5.2 ENANTIOSELECTIVE CO-POLYMERIZATION OF a-OLEFINS

AND CO

Consiglio and CO-worker first reported," in 1992, the preparation of isotactic propyleneK0 copolymers using chiral bidenate phosphorus ligands on the Pd catalyst (Eq. 1-10). The CO-polymerization of styrene and CO was canied out using a catalytic systern based on palladium acetate modif?ed with the atropoisomeric chiral ligand (6,6'- dimethylbiphenyl-2.2'-diyl) bis (dicyclohexy~phosphine) ?7

The '%-NMR spectra of the polymer correspondhg to the methyl group, showed a set of 4 lines in the 16-18 ppm region of the spectnun, in an approximate ratio of 13:72:9:6 (Fig. 6). These signals were assignecl to the four possible triads,16 RRR or SSS, RSR or SRS, RSS or SRR, and RRS or SSR. A aiad represents the absolute configuration of a senes of three repeating units within the polymer chain (Fig. 7).

Fig. 6 13C-NMR spectmm of the methyl group region for P/CO copolymer15

Fig. 7 RSR niad of oleWC0 copolymer

Using a staîktical approach, they found the tria& disuibution to correlate with a prevailing isotactic structure. However, no optical properties were reported to confinn their results. In the same paper, Consiglio reported also that s tyrenK0 co-polymerization using a non-chiral palladium catalyst gave a poIymer with a syndiotactic structure. Similar r d t s were reponed subsequently by sen.16 These results suggest that in the absence of a chùal catalyst, a chain-end control mechiinism controls enantioface selection.

In 1994, ~rookhad ' reported the synthesis of a highly isotactic, optically active poly(4-tert-butyhtyrene-alt€O) CO-polymer using a palladium catalyst incorporating an enantiomeridy pure C+ymmetric bis-oxazoline ligand (Eq. 1-1 1).

In addition to the high molar rotation observed in the polymer, the 13C-NMR spectra in the C(2) region (Fig. 8) showed only one signal, assigned as a RRR triad, demonstrating a stereoreguiasty greater then 98%.

g 8 "c-NMR spectra in the region of the C(2) resonance of poly-(4-tert- butylstyrene-alt+xrbon monoxide)"

Brookhart also proposed a iramition state for acyl migration to a prefered olefin enantioface, accomting for enantioselectivity during chain growth. (Fig. 9)

Fig. 9 Transition state for acyl insertion

These results by Consiglio, Sen and Brookhart indicate that when a planar, non- chiral bideritate ligand is used on the polymerization catalyst, the mecha- of chah propagation is chain-end controlled, giving a syndiotactic CO-polymer. Ou the other hand, by using an emtiomerically pure q-symmetric ligand, a strict enantiomorphic site controls the chain growth to produce highly isotactic, optically active CO-polymers.

1.2 IMINWCO CO-POLYMERIZATION 1.2.1 INTRODUCTION

In the previous section, it was shown that olehnlCO copolymerization is a well estabiished route to polyketone preparation. Nevertheless, therie is no information in the

literahxe conceming the CO-polymerization of CO with unsaturated substrates other than those with C-C multiple bonds (e-g olehs , alkenes). This is the case for imines (RzC=NR), which are isoelectronic to olefins. The interest in using imines as insertion monomers lies in their potential ability to fom new carbon-nitrogen bonds. Perhaps most interestingly, the use of imines, rather than olefins, with CO in an alternating CO-

polymerization would generate the poly-a-amide backbone of a polypeptide (Eq. 1-12)- If

performed with the appropriate R and R' substituents, this process would represent a unique and unprecedented metal catalyzed route to polypeptides, as an alternative to

conventionaï peptide syntheses. Considering range of readily avaiiable imines," such a process would provide significant advamages over amino-acid b d synthetic routes to peptides. Nevertheless, the alternating co-polymerization of imines with CO has not been descnbed. Pnor to discussing the background to imine/CO CO-polymerïzation, a brief overview of conventional peptide synthesis is presented

1.2.2 CONVENTIONAL PEPTIDE SYNTHESIS Classical approaches to peptide synthesis consist of protected amino-acid solution

chernistry. For example, the synthesis of the dipeptide Glycylalanine (Gly-Ala) can be obtained by reacing an N-protected glycine with an acid protected alanine, thus avoiding polycondensation berneen amino-acids unïts. The two uni& are coupled together via condensation of the acid terminus of Gly with the amino terminus of Ala, using

dicyclohexylcarbodiimide W C ) as a coupling agent Ihe final dipeptide is obtained by removing the protecting the groups (Scheme 4)-

Scheme 4. Solution synthesis of Gly-AIa

Considering the multiple protection and deprotection steps required, the solution synthesis of long chain polypeptides is time consuming, and also limited by technical diffculties, such a s solubility and purification problems. In 1962, R B .Memfieldw (Nobel Prize, 1984) proposed a new approach to peptides synthesis, the Solid Phase Peptide Synthesis (SPPS). This involved attachent of the growing peptide chah to a polymer m i n which acts as a support for the reaction. nie main features of Memfield's peptide synthesis are summarised in Scheme

Scheme S. Merrifield Peptide synthesis

Step 2TFA Step 3. AAUDCCYDMF u

The polymeric resin employed is usually polystyrene and acts as both a protection for the carboxylic acid terminus of the peptide and as an anchor. Following the attachent of the hrst amino-acid to the support (step l), de-protection of the N-terminus (step 2) and

condensation with a second amino acid (step 3) yields a dipeptide. 'Ihe use of excess reagents ensures high yield of the f i a l product The excess reagents cm be easily removed by washing the resin with solvent, while the growing peptide remains attached to the

polymenc support and on be extended hiaher in subsequent deprotection (step 2) and

addition (step 3) reactions. The polypeptide is hai ly cleaved off the resin using fluoridnc acid and coUected by washing with solvent While this process has been employed very successfally to prepare polypeptides, the use of excess reagent in each step makes the process expensive, especially for large scaie peptide synthesis. In addition, its reliance upon amino acids severely limits the types of peptides that can be prepared?

1.2.3 A P0TENTIA.L IMINE/CO CO-POLYMERIZATION ROUTE TO POLYPEPTIDES 1.2.3.1 INTRODUCTION

Considering the mechaniSm of oleGn/CO CO-polymerization (Scheme l), one could expect that a simiiar process, using isoelectronic imines rather then olefins, would also be

feasiile. The main difference between these two processes wodd be the migratory insertion of an imine, rather then oIefin, into the Pd-acyl bond (Eq- 1-13)-

Despite the similariries of olefins and imines, exampies of imine insertion into a transition metalcarbon bond are extmmely rare in the literatare? Indeed, pnor to the

research done in our laboratory, the only demonstrated exarnple of an imine insertion into a metal-carbon bond that we are aware of was reported by M& with the highiy electropositive Sm complex 20 (Eq. 1- 14).

However, early metal complexes are not prone towards subsequent insertion into the robust Sm-N bond, thereby making these impractical as CO-polymexization catalysts. To our knowledge, ttiere are no examples of imine insertion reactions with late metal--1 bonds. This contrasts with imine insertions into late metal-hydride bonds, which have been directly observed and posnilated in many metal catalyzed imine hydrogenation~?~

The lack of imine insertion mctions with late metal-alky1 bonds cm be explained by

examining simple bond energies. In contrast to early metals, late traasittion metal nitrogen- sigma bonds are known to be weaker? Thus, the insertion of imioe is expected to occur with the opposite regiochemistry to forrn a M-C bond (Eq. 1-15), However, based upon simple bond energy calculations, this reaction is predicted to be endothermic (ca. + 1

kca~mol)?' making the insertion (and for that matter the polymerization) of imine an energetically unfavourable process,

However, when carbon monoxide is included in the system, i.e. when there is sequential insertion of CO and imine into the M-alkyl bond, the energetics of irnine insertion change dramatidly. This This because imine insertion now occurs into a M-acyl bond, and results in the formation of a very strong amide bond. Indeed, simple bond energies2' predict that the alternating insertion of CO and irnine is even more exothermic than the well lmown o leWC0 system (Fig. 10).

Fig. 10 Themiodynamics of olefin/CO and imine/CO CO-polymerization reactions

While weIl denned examples of imine insertion into late metal-acyl bonds have also not k e n reported, they have been suggested as possible intermediates in several systems. These are summerized below.

1.2.3.2 POSTULATED IMINE INSERTION WITH CH,COCo(CO),

Alper reported,= in 198 1, that the reaction of acetylcobaltcarbonyl2 1 with a-keto

imines affords an acetamide (22) as the pnncipd product, as weU as a propionamide species (23) as a by-product of the reaction (Scheme 6)

Scheme 6. Ami& synthesis mediateà by cobalt carbonyl complexes

Wide the mechanism of this reaction is not known, it was postulated that imine insertion into the cobalt-acyl bond is involved (Scheme 7). Interestingly, the field of fonnation of the product 22 has been found to Vary with both electronic and steric

properties of the aromatic R group bom by the imine niuogen. Electmn donating groups at

the para-position lead to an increase in the reaction yield, while more sterically encumbered aryl groups were fomd to decrease the reaction yield (Table 1).

Table 1. Conversion of (Ar')(ArCO)C=NR to 22 at 60°C

R= - Reaction time @Ir) field- (%-

4-CH,C6H, 10 74

4-CH30C,H, 7 88 Ph 24 40

2 9 4- (cHJ&6H3 120 21 29 6-(CH3)2C6H3 120 6

From a gualitative point of view, it is possible to relate Ulis data to the rate of the

reaction. While the eiectronic effect on hine insertion is rather difficult to predict, steric

innuence is likely to decrease the reaction rate for more stericaliy encumbered imines, which îs the observed behaviour. This supports the possibility of amide formation through an imine insertion step.

1.2.3.3 Postuiated Imine Insertion With Fe,(CO),(R-DAB) An interesting example of possible imine inseaion was also described by Vrieze?

studying the reactïvity of alkynes with Fe@))6(R-DAB) (R = i-Pr, c-Hex) 24, Vrieze observed products which were consistent with imine insertion into a fomed iron-acyl bond (Scheme 8.).

Scheme 8. Postulated imine insertion into an Fe-acyl bond

imine insertion

Interestingly, a x-coordùiated irnine intermediate 25 is poslulated to form prior to

insertion. In contrast to olefins, x-coordinated imines of type II (Fig. 11) are rare, and

instead irnines prefer to bind to metals through their more basic lone pair (type I). Stable x-

coordinated imines of type II have been reportai only for strong backbonding early transition metalsu For example, RothwelIU presented an example of a complex containing

both an q2-imine and an ql-iminoacyl (26).

Fig. 11 GO and x-bonding mode (II) of an imine to a transition metal. Example of a R-bonded irnine 2644

1.2.3.4 POSTULATED IMINE INSERTION WITK TRICARBONYL (VINYLKETENE) IRON (O) COMPLEXES

More recentïy, Hegedus reportedm the reactions of ûicarbonyl (vinyktone)

iron(0) complexes with a number of imines to produce aicmbnyl-(q3-ayl-ql--1)

iron(0) complexes 28 (Eq. 1-16).

(Eq. 1-16)

This product could be considered to result fiom a formal insertion of the imine into the iron-acyl bond of 29 which is a resonance structure of 27 (Eq. 1-17). However, a direct nucleophilic attack of the imine niaogen on the ketene carbonyl group was not rejected as a possible path for that reaction.

1.3 THE ALTERNATIRTG INSERTION OF CO AND IMINE INTO A

Pd-CH3 BOND Very tecently, our groupZL reported the fUst directly observed example of imine

insertion into a late metal-acyl bond. A smnmary of the wo* done is presented below.

The Addition of TolOC=NR to the palladium compIex @ipy)Pd(CH3)NCMe'OTf

resulrs in the formation of the q'-coordinated imine adduct 3ûa-d m. 1-18).

Tol = p-CH3C&T4

OTf = Trifiate anion

1 + OTf (Eq*

130°C N-R - NR.

This coordination of imine has been shown to be reversible at room temperature in CD3CN, and the thennodynamics of this binding have been studied (Table 2).

Table 2. Tmine binding constants for 32a-d.

R K ~ a AH (kcaVm01)" AS (cal/mol)"

3 . X PhCH, 7.1x10-~ 8.7 (I0.9) 10 ( S I Ph 2 . 9 ~ 1 0 - ~ 6.6 (M.3) 10 (k1) 'Bu 1 . 4 ~ 1 0 - ~ 6.1 (W.2) 7-2 (M.5)

Weasured by 'H NMR at 30°C for: 32a.d + CDFN t, 30 + 31a-d. bFrom plot of K, vs. 1/T from 25-75°C.

Unlike olefins, imines do not insert into the Pd-Me bond of 32, even at high temperatures. This is consistent with the thermodynamics of imine insertion into a M-akyl bond, which was predicted to be an unfavourable process (1.2.3.1). The addition of 1 atmosphere of CO to 32a-d in C&C& leads to the formation of the piillsniurn-acyL

complexes 33a-d (Eq. 1- 19).

1 + OTf

These complexes have k e n shown to be stable at room temperature. However, when heated at 70°C under a CO atmosphere, M e inserts into the Pd-acyl bond, forming a 5 member metallocycle 34a-c (Eq. 1-20).

TOL a TOL R

The x-ray crystal structure for complex 34b (Fig. 12) has been obtauled, and

confirms that the imine insertion has occurred with the predicted regiochemistry. An

important feaaire conceming this structure is the high degree of conjugation berneen the

amide and the palladium. The carbon-nitmgen C(13)-N(3) bond length is relatively short (1.33A) compared to typical C-N amide bond (1.38&?' Also, the carbon-oxygen C(13)- O(1) bond length is simiificantly longer (1.26A) than a typical amide bond (1. This

indicates an important stabilization of the metalloçycle due to the resonance structure shown in Eq- 1-20.

Figure 12. Molecular structure of 34b. Selected bond lengths (A) are as follows: Pd- 0(1), 2.008(6); Pd-C(12), 2.022(8); O(1)-C(13), 1.265(10); N(3)-C(13), 1.328(11); N(3)-C(12); 1.498(lO)-

Sïxnüar results have since been reported by sen," using a cationic Pd@) sysrern with N and P-donor bidentate ligmds (Eq. 1-2 1).

The stmcture of these products of irnine/CO insertion are analogous to those obtained in oleWC0 co-polymerization 11 (Scheme 3). However, pre- expeiments to obtain successive insertions of CO and imine with complexes 34a-c failed to yield any new insertion products. For exampIe, when 34a-c are reacted with excess

Tol(H)C=NMe under 600 psi of carbon monoxide at 150T for I day, no poly-insertion product are formed (Eq. 1-22)."

StabjJization of complexes 34a-c through ir-conjugation with the palladium centre (eq. 1-20) has been posnilated to be responsible for the low reactvity observed. Relared research are stül under investigation in our laboratones, and wüi be the subject of the next chapters in this thesis.

REFERENCES

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(2) Crabtree, RH. The Orgmmetallic Chernidry of the Transition Metakr, 2nd edition, Wiley-Interscience: New-York, NY, 1994

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(7) Sen, A.; Lai, T.W. JArnChenSoc. 1982, 104, 3520-3522

(8) (a)Markies,B.k; Kniis, D.;Boersrna, J. JAmChemSoc. 1995, 117, 5263- 5274. (b) Piet, V.N.; Van Leeuwen, M.; Roobek, C.S.; Van der Heijden, H. J.Am.Chem.Soc. 1994, 116, 12117-12118. (c) Van Asselt, R.; Gielens, EX.; Rüike, R.E.; Vneze, K; Wvier, C.J. JAmChemSoc. 1994, 116, 977-985. (d) Bathini, A; Consiglio, G. Orgmmerallics, 1992, 11, 1766-1769. (e) Bnunbaugh, J.S.; Whittle, RR.; Parvey, M.; Sen, A. Organometallics 1990,9, 1735-1747.

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(10) Lai, T.W.; Sen, A Organometallics 1984,3,866-870

a (11) Chen, J.T.; Sen, A JArn.ChemSuc. 1984, 106, 1506-1507 (and references

therein)

(12) Cowie, J U G . Polymers: Chemistry & Physics of Modkm Materiak, 2nd ed. Blackie Academic & ProfessionaI, Glasgow, 199 1. P. 123

(13) Sen, A; Jiang, 2. Macrumolecules l993,26,9 11-915, and references therein

(14) See (12), p.125

(15) Barsacchi, M.; Bat- A; Consiglio, C.; Suter, V.W. Macromlecuies 1992,

25,3604-3606

(16) Sen, A; Zhaozhong, J. Macromlecules 1993,26,911-915

(17) Brookhart, M.; Wagner, MI. JAmChemSoc. 1994, 116, 3641-3642

(18) (a) Sperrle, M.; Consiglio, G. J.Am.ChemSoc. 1995, 117, 12130-12136. (b)

Nosaki, K; Sato, N.; Takaya, H. 3.Am.ChemSoc. 1995, 117, 9911-9912. (c) Jiang, 2.; Sen, A- JAmChemSoc. 1995, 117, 4455-4467. (d) Jiang, 2.; Adams, S.E.; Sen, A.

Macromolecules 1994, 27, 2694-2700. (e) Xu, F.Y.; Zhao, AX; Chien, J-C-W- Màk~omaLChem 194,2579-2603 (1993).

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(20) Most of simple N-alkyl alnimine or ketimine are prepared by a simple condensation

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(24) Frymck, MD.; Piers, W.E. Orgmzometallics, 1990, 9, 986-998, and references

therein.

(25) For lead references: (a) Willoughby, CA.; Buchwald, S.L. LAm. Chem. Soc.

1994, 116, 11703-11714. Q) Fry* MD.; Piers, W.E. Orgammetallics, 1990, 9, 986-998. (C) Burk, M.J.; Feaster, LE. JAmChemSoc. 1992, 114, 7266. @) Bakos,

1; Orosz, A; Heid, B.; Laghman, M.; Lhoste, P.; Sinou, D. J-ChemSoc.,

ChemComm, 1991, 1684. (E) Spindler, F.; Pugin, B.; Blaser, H.O. Angew-Chem.,

Int-Ed-Engl,, 1990, 29, 558. (F) Chan, Y.N.C.; Osbom, J.A. J.Am,Chem.Soc. 1990,

112, 9400. (G) Becker, R; B m e r , H.; Mahbwbi, S.; Wiepebe, W. Angew. Chern.,

Int.Ed.EngL, 1985, 97.

(26) Willoughby, C.A.; Buchwald, S.L. J A m ChernSoc. 1992, 114, 7562.

(27) Typical C-N and C=O amide bond length are for fonnamide HCON& Ref: Hmdbook of Chemistr y and Physics, 50th edition, The Chemical Rubber Co., CIeveland,

1969

(28) Greenstein, J.P.; Winïtz, M.W. CheMstry of the a m h acids. Vol 2. John Wdey

and Sons, Inc., NewYork, N.Y., 1961.

(29) MerrifieId, RB. Fed Proc. Fed. Amer-Soc-Exp- Biol-, 2 1, 412.

(30) Memneld, RB. JAmChemSoc. 1963. 85, p.2149.

(3 1) For a review: Barany, G. And Merrifield, RB. (1979) In The peptide, Gross E. And Mecenhofer J., (eds.), vol. 2, academic Press, NewYork,

(32) Despite the Mted application of SPPS for large peptides prepamtion, this synthetic

meîhodology has evolved an intense field of research related to smali peptidornimetic

synthesis called Combinatorial Chemistry. Description of combinatorial chemistry is not

relevent to this wock. For good review, see: (a) Fruchtel, J.S., Jung, G. Angew.

ChemInt.Ed.EngZ- 1996, 35, p-17- (B) Houghten, RA., Nefzi, A-, Ostresh, LM. ChemRev- 1997, 97, p.449. (c) Hermkens, P.H.H.; Ottenheijun, H.C.J., Res, D.

Tetrahedron, 1996, 52, p. 4527.

(33) (a) Hartley, G.H.; Guillet, T.E. Macromolecules, 1968, 1, 165. (B) Guillet, J.E.;

Dhanrag, J.; Golemba, F.J.; HartIey, GH. A h - Chem Ser. 1968, 85, 272. (C)

Heskins, M,; Guillet, J.E. Macromolecules, 1970, 3, 224,

(34) Brubaker, M.M.; Coffman, D.D,; Hoehn, H.H. J. Am.Chem.Soc, 1952, 74,

1509-

(35) Safir, A.L.; Novak, B.M. JAm-ChemSoc. 1998, 120, 643-650.

(36) Guido, P.C.M.; Cornelis, LE.; Vrieze, K.; van Leewen, P.W.; Roobeck, C.F. J.

of Organornet. Chem. 1992,430, 357-372.

(37) Drent, E.; van Broekhoven, XAM.; Doyle, M.J. J. of Organomet. Chem 1991,

417, 235-25 1.

(38) Markies, B.&; Rietveld, M.H.P.; Boersma 1.; Spek, AL.; van Koten, G. J o u d

of Organornet. Chem. 1992,424, C12-C16.

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5895.

(40) van Asselt, R; Gielens, ECG-; Rulke, R.E.; Vneze, K.; Elsevier, C.J. J . A n Chem-Soc. 1994, 116, 977-985.

(41) Vollhardî, P.C. Traité de Chimie Organique , Edition Universitaire, Park, 1990.

(42) Obora, Y.; Ohta, T.; Stern, CL.; Mark, T.J. J.Am. Chem Soc. 1997, 1 19, 3745-

3755.

(43) Sando~Q, C. The Chemisv of the Cmbon-Nitrogen Double Bond; Patai, S. Ed.; Wiley: New-York, 1970: p.1.

(44) Durfee, L.D.; Fanwick, P.E.; Rothweil, LP. J A m ChemSoc. 1987, 109, 4720-

4722-

(45) Kacker, S.; Kim, JS.; Sen, A- AngewXhem,Int.Ed-Engl., 1998, 37, no.9.

(46) The presence of a new product was observed (c stoechiomenic relative to III), but it could be aürîbuted to the presence of moisaire in the carbon monoxide gas employed. Further investigations are required to establish exactly the mctivity of these complexes. Nevertheless, no polyinsertion product was observed.

(47) Miyastiita, A.; Karino, Ha; Takaz, A. Chern.Lett. 1989, 1849.

CHAPTER 2: GENERATION OF IMINE INSERTION PRODUCTS USING COBALT CARBONYL COMPLEXES

2.0 OBJECTIVES

As discussed in the nrst chapter, imines have been shown to insert hto the

palladium-acyl bond of 33a-c to generate a stable product (Eq. 2-1). However, no

evidence for the formation of a poly-a-amide polymer was observed when complexes 34a-

c were reacted with excess irnine under high CO pressure (600 psi).

1 + OTf To

70°C - (Eq. 2-11

R

Io order to perform the next step in the imine/CO CO-polymerization process, there is a crucial need for a fke coordination site that would allow CO coordination prior to

insertion into the Pd-carbon bond of 34 (Eq. 2-2).

IutereStiLlgly, x-ray structural characterizaîion of complex 34 (R = Me) revealed an unusual shorty C-N amide bond dong with a long C=O amide bond, indicating a high

degree of interaction between the chelated amide and the palladium centre. T'us, metallocycle 34 can be regarded as being in equilibrium with the resonance form 34' (Eq. 2-3).

This important sîabilizaîion effect might seriously impede the formation of a free coordination site, and prevent m e r insertions fiom o c c ~ g . Therefore, it is possible to predict that a successful catalyst for imindC0 CO-polymerization would require a metal centre that binds less tightly to the amide oxygen. One possible way to acbieve thjs would be to use a more electron rich metal catalyst. A more e--rich metal would be l e s Lewis acidic, and therefore bind less tightly to the amide oxygen. This would provide greater access to a coordination site on the met&

In light of this argument, the work descnbed in this chapter wIU involve the use of a neuaal transition metal complex as a potential catalyst for the the CO-polymehtion of imine and carbon monoxide. As discussed in chapter 1, ~ l p e 8 ~ bas shown that alkyl cobalt tetraçarbonyl reacts with imines to yield amides. This reaction likely proceeds through the sequential insertion of CO and imine into the Co-alkyl bond (Scheme 9), however no mechanhic information is availab1e concerning this reaction.

This example stirnulated our interest in studying the use of cobalt aOryl teûacarbonyl complexes for the imine/CO CO-polymerization 'Ihe insertion of imine into the cobalt-acyl bond would be expected to produce an intemediate similar to the palladium complex 34.

However, a neutral meiallocycle is expected to be more prone to open and mate a fiee coordination site for an incoming CO ligand than the corresponding cationic Pd@) system (Eq. 2-4). In addition, the CO ligand bonded to the cobalt centre cau possibly allow the subsequent CO insertion into 35 to occur in au htramoIecular fahion, negating the

need to generate a free coordination site to perform m e r insertion steps (Eq. 2-5).

2.1 N-METHYL-TOLUALDIMINE INSERTIONS WITEï (CO),Co(COMe) 2.1.1 STOICHIOMETRIC REACTIONS

Acetylcobalt tetracarbonyl21 can be fonned "in situ" by the reaction of sodium cobalt tetracarbonyl and methyl iodide under one atmosphere of carbon monoxide (Eq. 2-

6)- When this reaçtion is performed in CD3CN in the presence of N-methyl-tolualdimine 31a, monitoring the reaction by 'H-NMR shows the inmediate formation of 21 and a broadening of the imine peaks. Afîer 1 hour, several new species are formed dong with a decrease in signal intensity for both N-methyl-tolualdimine and acetylcobalt tetracarbonyl. After 8 hours, no more acetyl cobalt teiracarbonyl is seen, and the NMR spectra display a very complex pattern, indicaing decomposition or multiple reactions. The appearance of several new peaks between 5-6 ppm is encouraging, considering that it is approximately the

expected chemical shift for a reduced imine (Fig. 10). This would be consistent with imine insertion into the cobalt-acyl bond. However, wider no reaction conditions ( low temperature, non-coordinating solvent, excess ïmine) codd any isolable materiais be obtained.

6 = 5-6 ppm

Fïg. 10 Expected 'H-NMR chemical SM for reduced imine hydrogen

2.1.2 ATTEMPTED (Tol)HC=NMe/CO CO-POLYMERIZATION AIkyl trausition metal carbonyl complexes are lmown to be in equiliïrium witb their

CO insertion product? (i-e. M-acyl) (Eq. 2-8). At elevated CO pressure, the equiiibrium is shifted far to the acyl complex and kl » > k-,.lS

Considering that acyl-cobalt tetracarbonyls are more stable than their alkyl analogs,16 it is conceivable tbat the product of imine insertion into a Co-C(0)-CH, bond

could be stabilized, pnor to the next imine insertion step, by pushing the equilibnum toward their acyl derivatives (Eq. 2-8).

Thus, attempts were made to CO-polymerize TolOC=NMe and CO under high CO pressure. Equimolar amounts of sodium cobalt tetracarbonyl (30 mg, 0.16 moles ) and methyl iodide (22 mg, 0-16 mmoles) were dissolveci in 3 ml of a 1:1 solution of Cq,CN:Tol(H)C=NCH, and the solution was reacted at 60°C for 12 hours under 600 psi of carbon monoxide (Eq. 2-9). The excess imine was then removed under high vacuum (50 mtorr @ 50°C) and the residue was examined by 'H-NMR No pealcs of interest (5-6 ppm) were present on the spectra, which contained mainiy decomposition products.

CO, 600 psi 5Q°C, 12 hours

NaCo(C0)r + Me1 + k ~ m p . + H M e H M e

"excess"

2.2 ATTEMPTED SYNTHESIS OF (CO),Co[(Tol)HCN(Me)COPh] 2.2.1 OBJECTIVES

The reactions of Tol(H)C=NMe with acetylcobalt tetracarbonyl has ken covered in the previons section. These showed îhat a reaction of imine does occur, and by 'H-NMR evidence of imine insertion was observed. However, these reactions leads to the formation of multiple products and unidentifiable residues, possibly due to the instability of the product formed by the insertion of N-methyl-tolualdimine into the cobalt-acyl bond. Another approach was thus investigated to prepare these compounds. Specifically, the

addition of sodium cobaltate tetracarbonyl to N-a-chloroalkylamide (36) derivatives should

lead to the same "imine insertion product" as is expected for the insertion of imine into a cobalt-acyl bond. Tbis would allow the possibility of studying direcîly the stability and reactivity of these molecules under more mild conditions (Eq. 2-10).

Tol

39

(Eq. 2-10)

2.2.2.1 N-a-CHLOROALKYLAMIDE SYNTHESIS

N-a-chloro-aUq1amide-s 36a-b were prepared using a modified Literatme

procedure." Reaction of N-ml-tolualnimine 31a-b and benzoyl chloride in CH3CN for 15

minutes lead to the formation of the corresponding N-a-chloro--lamide 36a-b (Eq. 2-

21). These compounds c m be isolated by crystallizattion in approximately 50% yield.

36a: quantitative 36b: 75% yield

Compounds 36a-b were characterized by 'H and 13C-NMR. Of note, the 'H-NMR

for 36a displayed an upfield shift for the N-methyl signal (6 = 2-76)? and an upfield shift in

the imine hydrogen C-H (6 = 7-52), consistent with the imine reduction. In addition, the

13c-NMR spectra show a typical value (6171.9 ppm) for an &de carbonyl group.

2.2.2.2 REACTION OF N-a-CHLOROALKYLAMIDE WITH SODIUM.

COBALT TETRACARBONYL

Equimolar amounts of N-achlor~alkylamide 361 and sodium cobalt tetracarbonyl

were dissolved in 1 ml of CD,CN and the reaction was followed by NMR (Eq. 2-12).

After 15 minutes at room temperature, 36a is completely consumed and the 'H- NMR spectra shows an unidentifiable mixture of products. The same reaction under 1 atm. of carbon monoxide does somewhat perturb the formation of these products, suggesting that the metaï mtre is still attached to the organic fragment, and that CO is involvd in the

reaction. The 'H-NMR for reaction 2-12 shows some similarities to that observed for the M e insertion reaction (Eq. 2-6), suggesting that these reactions proceed through similar

"addition" Ph

(W. 2-13)

decomposition

Although no products can be isolated and identifïed from these reactions due to the

complexity of the mixture, these results are somewhat encouraging. Namely, the spectral data strongly imply that imine reduction (Le. insertion) is o c c ~ g , foUowed by decomposition. Thus, these products of imine insertion appear to be extremely reactive when compared to the inca palladium analogues, Aüempts to prepare more stable versions of these complexes are explored below.

2.2.3 ATTEMPTED TRAPPING OF [(CO),CoC(H)(Tol)N(Me)(COPh) J WITH PPh, 2.2.3.1 OBJECTIVE

Tertiary phosphines are the most commonly encountered anciliary ligands assocïated with organotransition metal compounds? In the case of cobalt aJkyl complexes, it has been shown7 that triphenylphosphine can "trap" the product of insertion of alkyl cobalt tetracarbonyl to form stable acyL derivatives (Eq. 2- 14).

It is also hown that metal carbonyls substituted with iuylphosphine ligand are more stable and easier to isolate then their non-substituted ana10gs.~ Thus, our interests in using niphenylphosphine lie in the potential use of these ligands to stabilize the addition product

of N~CO(CO)~ and N-a-chloro-aikylamide, in analogy to the chemisay of (CO),Co-CH,

In order to tmp complex 37 (Eq. 2-15) as it is formed, iriphenylphosphine and N-

a-chloroaIkylamide must be present in solution. However, a control reaction showed thaî

they react together to form a phosphonium salt derivative (Eq. 2-16).

Another approach was then considered, which consist in the cobalate addition to the

phosphinium salt derivative, where triphenyl phosphine acts as the leaving group instead of

chloride IEq. 2-17). These resvlts are presented below.

2.2.3.2 SYNTHESlS OF N-a-PHOSPHINIUM-ALKYLAMIDE

Equimolar arnoants of trimethylace~lchl~nde,~~ Tol(H)C=NMe and

triphenylphosphine were reacted in ether at room temperature for 2 hours to generate the

corresponding N-a-phosphinium-aikylamide derivative 38 (Eq. 2- 18) .

Product 38 was isoiated by crystallization in 54% yield and was characîerized by

NMR spectroscopy. The 'H-NMR display signals at: 6 7.63-7.75 (m, 9H, PPh,), 7.5 1 (m,

6H, PPh,), 7.12 (d, 2H, TOI), 7.00 (dd, Jw = 3.5 HZ, ZH, Tol), 6.M (d, 'J,, = 11 HZ,

lH, Hl), 3.43 (d, 4~p-n = 2.7 HZ. 3H, N-CH3), 2.30 (d, 2 ~ p - E = 2.2 Eh. 3H, Tol-CEZ3) and

1.01 (s, 9H, C(CH3)3). The coupling of Hl with the phosphorus is consistent with the

proposed structure, with a coupling constant (2~,, = 11 Hz), in the range of what is

expected for a 2 bond P-H coupling in organic molecules (TH=-, = 0.5-20 Hz).18 The 13C-

NMR spectra show a peak at 6178.3 ppm (d. 3J,, = 7.6 Hz) corresponding to the carbonyl

amide, confirming the formation of an amide bond. The Large phosphorus-carbon couphg

constant of C* ('J,, = 260 Hz) is in agreement with formation of a carbon-phosphorus

bond. Interestingly, coupling of phosphorus with other nuclei is usually O bserved through up to 4 bonds," which is observed for the quatemary carbon of the nimethyl group in 38,

with a chcniical shift of 20.4 ppm and a small coupling constant of 4 ~ p c = 5 Hz

2.2.3.3 REACTIVITY OF 3 WITEI NaCo(CO), A) ROOM TEMPERATURE REACTION

When 38 is reacted with equimolar amouats of sodium cobalt tetramrbonyl in acetonitrile at room temperature, the new product 39 is formed in almost quantitative yield

'H-NMR 6 Hl 650 (d) 2 ~ ~ - ~ = 1 1 hz 31~-NMR 6 P 19.85 *c-NMR 6 C* 60.7 (d) 2~p_C = 260 hz

IH-NMR 6 H~ 5.77 (d) 2~p-H = 11 hZ

"P-NMR6P 19.90

U~-NMR 6 C* 63 .O (d) 2 ~ ~ - ~ = 265 hz

IR CO (ami&) 1596 cm-'

IR CO (cobaltate) 1882 cm1

Product 39 was isolated by precipitation as a light brown powder in 57% yield. The 1 H-NMR shows characteristics peak at 67.51-7.74 (m, 15H, PPh,), 7.15 (d, 41,, = 8.4

HZ, ZH, TOI), 6.95 (dd, 4JH-E = 8-4 HZ, 4~p-H = 2-0 HZ, 2H, TOI), 5.77 (d, = 11 HZ, lH, Hl), 3.33 (d, 4J,, = 2.5 HZ, 3 8 N-CH,), 2.3 1 (d, J,, = 2.2 HZ, 3H, Tol-CH,), 1-01 (s, 9H, C(CH,),). An important feature of this spectra is that H, is still coupled with

the phosphorus, indicating mat cobaltate carbonyl anion did not displace PPh,. Further midence of the latter consist in the strong coupling between C* and P (2~,, = 265 Hz), almost identical to the parent compound 38. In addition, the IR specm show the major absorption band in the metal-carbonyl region at 1882 cm", the expected signal for cobaltate tetmcarbonyl anion." Based on these fïndings. the siructure of complex 39 was assigned to be the anion exchange product of 38 and NaCo(CO),

The large upfield chemical shift (- 0.7 ppm) observed in the 'H-NMR for Hl upon king converted fiom 38 to 39 is unusuai for a simple anion exchange reaction. Thus, a control reaction was perfomed by adding sodium ûifiate or sodium tetraphenylboron to 3 8

(Eq. 2-20) to generate the corresponding sait 4Oa- b with non-bonding counteranion. Indeed, 'H-NMR signals for Hl of 5a-b show chemical shift almost identical to 4, which suggest that cobaltate tetracarbonyl acts as a non-binding comteranion.

X = OTT, BAG 40a- b

l~-NMR ma: X = OTf, 6H1 = 5.82d

40b: X = BAr4; 6& = 5.77d

(eq. 2-21)

B) REACTIVITY OF 39 AT 60°C

While cobalt carbonyl anion was f o n d to add to N-a-chloroaliqlarnide at room

temperature (Eq. 2-12), it only undergoes a simple anion exchange reaction with N-a-

phosphiniun-alkylamide (Eq. 2-20). It therefore appears the phosphine substituted N-a-

phosphinium-alkylamide is less electrophilic at carbon than 36a. This could be expected by

the nucieophilic disphcement of chloride by PPh,. However, addition of (CO),Co- to 39

can be achieved upon heating. When 39 is heated to 60T for 16 hours in CDFN, 'H- NMR displays a complex pattern similar to reaction 2-12, dong with fiee

triphenylphosphine (Eq. 2-21). This suggest dut cobaltate tetracarbonyl can add to N-a-

phosphinium-p la mi de, and also that triphenylphosphine does not trap the addition product to fonn a more stable intemediate.

2.2.4 ATTEMPTED TRAPPING OF [(CO),CoC(H)(Tol)N(Me)(COPh)] WITH Tol(H)C=NMe 2.2.4.1 OBJECTIVES

Io analogy to what has been presented in section 2.2.3, the use of an imine to trap

the addition product of cobalt carbonyl anion to N-a-chloro~lamide was investigated, as

a route to form a more stable cobalt complex (Eq. 2-22).

2.2.4.2 S YNTHESIS OF N-a-IMINIUM-ALKYLAMIDE AND

REACTIVITY WITH COBALT CARBONYL ANION

Simüar to the results with PPh,, it was found that Tol(H)C=NMe can add to N-a-

chloroaIky1-amide to fonn an iminium derivative. When trimethyl acetyl chloride was reacted with 2 equivalent of TolOC=NMe in CD,CN at room temperature (Eq. 2-23), rhe

'H-NMR of the solution showed an equilibriium between starting materiais and N-a-

iminium-alkylamide 41. Upon addition of one equivalent of cobalt carbonyl anion, the equtlibrium is shifted completely towards the anion exchange product, forming the new

complex 42 in quantitative yield by 'H-NMR

3 hours

decomposition H Me

Complex 4 1 and 42 were characterized by 'H-NMR The spectra for 41 show

rwmances at: 6 9-09 (s, IH, H,), 7.26 (d, 2H7 Tol,), 7.07 (s, lH, Hl), 3.75 (s, 3H,

Med. 3.03 (s, 3H, Me,), 2.39 (s, 3H, Tob-Me), 2.35 (s, 3H, ToIl-Me), 1.3 1 (s, 9H, C(cHJ3)- The large downfield shifr for both H, (9.09 ppm) and Me, (3.75 ppm) compared to ffee imine is consistent with the fonnation of an iminium cationic moiety.

Similarly, 'H-NMR for 42 show resonances quite similar to 4 1: 6 8.55 (s, lH, HJ, 7.93

(d7 2H, Tob), 7-58 (d, 2 X T&), 7.37 (d, 2H, Tol,), 7.27 (d, 2H, Tol,), 6.99 (s, lH, Hl), 3-72 6, 3H7 Mq), 2-96 (s, 3H. Me,), 2.52 (s, 3H, Tol,), 2.40 (s, 3H7 TOI,), 1.35 6 , 9H, C(C)j[3)3)-

When a solution of 42 is aUowed to react at room temperature for three hours, a slow reaction occurs forming multiple products and fiez imine. After 48 hours, 'H-NMR spectra is complex and close to what is observed when 39 is heated in CD,CN for 16

hours, suggesting a similar mechanism where cobaltate anion adds to the N-a-substituted-

alkylamide to foxm an addition product that readiiy decomposes under the reaction conditions,

2.2.5 ADDITION REACTION OF N-a-CHLOROALKXLAMIDE WITEI

SODIUM COBALT TRXCARBONYL TRIPHENYLPHOSPHINE 2.2.5.1 OBJECTIVES

In light of the previous experïments, extemal ligands do not appear to be able to trap

the "in situ" generated product of addition of metal anion to the N-a-chioroalkylamide.

Thus, PPh, was incorporated directly onto the cobalt anion prior to reaction with 36. Considering that the lability of the carbonyl ligand bound to a cobalt tncarbonyl species is decreased when compared to teîracarbonyl derivatives,' subsequent reactiom such as CO

insertion or ligand substitution are expected to be les favoured, and could lead to a product sufnciently stable to be isola&

2.2.5.2 Preparation of NaCo(CO),(PPh,) Sodium cobalt tncarbonyl triphenylphosphine was prepared in 53% yield using

fiterature procedures: and involved reduction of the cobalt mcarbonyl triphenylphosphine dimer with a sodium amalgam in THF (Scheme 10)-

Scheme 10. Preparation of NaCo(CO),(PPh,)

When NaCo(CO),(J?Ph,) is added to a CD&N solution of N-a-chloro-aRqlamide

36a at room temperaaire (Eq. 2-24), an immediate da& brown colour i s fomed and a brown residue precipitates out of solution. The 'H-NMR of the residual solution is cornplex, and no discemible information was obtained concerning the I 1 t a r likelike" precipitate, due to its insolubility in ai i solvents tned. There is also no evidence that the cobalt anion add to the electrophilic substrate to form a Co-atkyl bond prior to decompositio~

2.3 Conclusion Attempts to use cobalt carbonyl complexes as catalyst for nnindC0 co-

polymerization, and to generate stable stoichiometric imine insertion products have not k e n successful. For ai l cases investigated, the complexity of the reaction mixture suggests multiple product formation and a complicated decomposition pathway after an initial imine inserfion product 37 is generated. Considering the chemistry of simple alkyl-Co(CO), complexes, this observation is not entirely unexpected. In general, the rates of formation and decomposition of the alkylcobalt tetracarbonyls approach each other and the yields are poor.' For example, methyl cobalt tetracarbonyl decompose at -35OC in its pure form. C h e of the common decomposition pathways is formation of diaikyïketone through a Co(iIi') acyl-alkyl complex as a key intemediate (Scheme 1 1)?

Scheme 11. DiaIkyIkeme fomiation fÏom alkyl tetracarbonyl

In contrast, the thennal decomposition of functionalized alkyl tetracarbonyl has ben

shown to involve radical pathways.1° For example, complexes of the type EtOOCCH(R)Co(CO), (R= Me, t-But, Ph, COOEt) are themaüy unstable and decornposition products analysis suggests the involvement of radical^.^' In fact, the

aIkylcobalt carbonyls can be regardeci as being in equilibrium with products of both heterolytic and homolytic cleavage of the alql-cobalt bond. The position of the equüibrirn depends very aitically on the nature of R(Eq. 2-25)?

Considering that imine insertion into the cobalt-acyl bond would generate a cobalt complex with R = -Ceol)HNRCOMe, the presence of an aromatic and amide group on the

a-carbon is likely to stabilize both homolytic and heterolytic cleavage of cobalt-çarbon

bonds (Scheme 12). This could jus- the decomposition observe&

eherne 12. Postulateci decomposition mode for (C0)4CoCE3(Tol)N(Me)(COMe)

In conclusion, the generation of irnine insertion products using cobalt carbonyl systems was unsuccessful due to the instability of the product formed. A product distribution study to determine the decomposition path in detail couid have been extremely demanding and is not relevant to this work Instead, the focus of our research rnoved to a similar manganese system known to form more stable MER bonds, as described in chapter 3.

References

Heck, R.F.; Breslow, DS- J- Am, Chem Soc. 1962, 84, 2499-

Clark, RJ. I. Orgrnomet Chem 1968, 11, 637.

Prepared using literature procedure: Layer, RW. Chem Rev. W63,63,489.

Zaugg, H.E. Synthesis, 1984, 85.

see ref. 1, chapter 1.

Galamb, V.; Palyi, G. Coordination Chemistry Reviews, 1984,59,203.

Heck, RF. J. Am. Chem. Soc. P963, 85, 1220.

Kieber, W. Chem Ber., 1961, 94, 1417.

Beck, W.; Nitschrnann, E. RI Chem Ber. 1964,97, 2098.

Palyi, G.; Ungvary, F.; Galamb, V.; Marko, L. Coordmoaon ChemLmy Reviews,

(11) Seyferth, D.; Millar, M.D. J.Organomet. Chem 1972, 38.

(12) Crabtree, RH. The ûrganometazlic Chemîrny of the Tr-tion Met& 2 m d ~ d . .

John Wiley & Sons, New-York, 1994.

(13) See ref. 23, chapter 1

(14) Ref. 22A, chapter 1.

(15) Calderazzo, F. Angew- Chem., ?nt. E h Engl,, 1977, 16, 299-3 11, and referaces therein.

(16) Cause, J.N.; Fiato, R A ; Pruetî, RL. Journal of Orgmzomet. Chem , 1979, 172, 405-463

(17) The use of benzoyl chloride lead to an incomplete reaction and isolation of the product could not be achieved.

(1 8) Silverstein, RM. Spectroscopie 1dent@catratron of ûrganïc Compourtds, 5th edition,

John Wiley & Sons, Inc, New-York, 1991.

(19) Basolo, F. Mechmtisms of Inorganic Reactions; a Study of Metal Complexes in

Solution, 2"d Ed-, Wiley, New-York, 1967.

CHAPTER 3: THE SEQUENTIAL INSERTION OF CO AND Tol(H)C=NMe PVITH MANGANESE COMPLEXES

3.0 INTRODUCTION The migratory insertion of CO in atkyhanganese pentacarbonyl complexes has

been extemively investigated.' In general, CO insertion is known to occur via two possible mechanirim: the forniaï insertion of CO into a transition metai--1 bond (Eq. 3-1) or dïql

migration to an adjacent CO Iigand (Eq. 3-2).

L* I CO insertion fi - L-MO

L L-M-CO

F' @+ 3-1)

A2 I

~alderazzo~ and ~lood' studied the stereochemical consequences of the

carbonylation of (CO),MnMe. Using a labelled carbon-13 carbonyl complex (Eq. 3-3), they found the product distribution to be consistent with methyl migration, that is a ratio of a:b:d of 1:2:1. Product c, which c m only be formed by a formal CO insertion into Mn-Me bond, was not observed. FloodR ais0 suggested a square-pyramidal intemediate which is rigid over the time scale of the reaction (Eq. 3-4).

The sequential insertion of carbon monoxide and other uasaturated substrates into a manganese-aikyl bond has &O b e n ~bserved.~ An interesthg example was descnbed by IIaszeldine and CO-worker," where me reaction of (CO),MnR @=Me, Ph) with dicyclopentadiene under a CO atmosphere leads to the formation of 42 (Scheme 13).

Scherne 13 Sequential insertion of CO and dicyclopentadiene into Mn-R bond of the complexe (CO)* @=Me, Ph)

slow - -

More recently, DeShon2 reported (Scheme 14) the regioselective insertion of alkynes or aikenes and CO into manganese-dQI bonds. The reaction can be performed with a variety of aikyimanganese pentacarbonyl complexes, and the intemediaies were used for the synthesis of E-enones (l), butenolides (2), or ketones (3).

Scheme 14. E-enone (l), butenolides (2), and ketones (3) synthesis using

While the sequential insertion of olehns and idkynes with CO hm been extensively stuclied with manganese complexes, the analogous chemistry with i . e s and CO has not been explored. As described previously (Ch. l), the altemaihg insertion CO-polymexization

of CO and imine would generate the poly-a-amide backbone of a peptide, providing an

attI;ictive route to such materialS. Sequential COhnine insertion has been previously noted to occur with the palladium complex @ipy)Pd(m)+OTf, however these Pd products were inert to subsequent insertion of CO (Eq. 3-5).

7+ OTf- I - - -

O R CO, 600 psi

-x- O 3 Co Tol O

The stabili. of palladium metallocycles of type 34 towards insertion is hypothesized to be due to strong chelation of the amide oxygen to the palladium centre. This

does not provide a site for CO to bind prior to inseaion. Similady to what has been

proposed previously for cobalt carbonyl complexes (chapter 2), chelation of the neutral manganacycle to the amide oxygen is expected to be less favoured when compared to tbe

corresponding cationic Pd complexes, uius making Mn complexes more prone to generate a fke site for an incoming ligand (Eq. 3-6).

In addition, the examples cited above show that alkylmanganese pentacarbonyl complexes are reactive towards the migratory insertion of u11sâturakd substrates, and thai

the products of insertion are stable and c m be isolated. For these reasons, the reacîivity of alkylmanganese pentacarbonyl with imines was investigated as a method to generate stable CO and imine insertion products (Eq. 3-7).

3.1 REACTIVITY OF IM3[NES Toi(H)C=NR WITEI ALKYLMANGANESE PENTACARBONYL 3.1.1 REACTION OE" (CO),MnR (R=Me,Ph) WITH TOI (H)C=NR' (R'=Me,Bz,Ph)

When (CO),MnR (R = Me, Ph) and imines Tol(H)C=NR' (R1=Me,Bz,Ph) 3 1 a-c are reacted in CDFN at 70°C, rather than the expected product of imhe insertion, the ortho-manganated species 43a-c are obsemed (Eq. 3-8). The formation of CH, or C,H, was also noted, for R = Me and R = Ph, respectively. The reaction times Vary fiom 1 and 5

days, and are relatively shorter for the l a s stericaUy encumbered imine 36a

434 (67% yield) 43b (70% yield) 43c (43% yieid)

43a-c were isolated in 43-7046 yield and completely characterized by 'H 13c NMR, IR and elemental analysis (43a-b). Of note, the 'H-NMR for 43a show a downfield shift

for both N-Me (6=3.42) and H-C=N signal (6=8.48) when compared to 3 la, consistent

with chelation of the imine nitrogen to the metaï centre withdrawing e- density fiom the

imhe moiety. Thtee inequivalent aromatic hydrogens of equal intensity are also present, demonstrating that metallation of the tolyl aromatic ring has occured The l3CXMR spectra

for 43a display six inequivalent armatic carbons and a downfield shift for the imine carbon fkom 161.9 to 176.1 ppm, also consistent with imine coordination to manganese

centre- Two Mncarbonyl resonances are observed in 7a (6 220.2, 214.6), as opposed to

the expected three. However, this was found to be due to overlapping resonance at 214.6 ppm, and indeed, the 13C-NMR spectra for 43c shows 3 different carbonyl signals ar 220.7, 214.5 and 213-6 ppm. It is &O relevant to mention that for the reaction of (CO),MnMe and 31a. a srnaii amount (5%) of a side product was detected by 'H-NMR, with signais at 5.12 and 3.00 ppm. As it wiii be demonstrated subsequently, this is the product of imine insertion.

3.1.2 REACTIONS OF (CO),1MnMe WLTH Tol((CH,),C ) C=NH The reaction of NH-ketimine To~((C~)~C)C=NH (44) with alkyhanganese

pentawoonyl has also been investigated. When methylmanganese pentacarbonyl is mixed

with NH-ketimine 44 in CD,CN at room temperature, the formation of manganese acyl-q1

bonded imine complex 45 is observed in alrnost quantitative yield (Eq. 3-9).

(Eq. 3-9)

45

quantitative

Complex 45 was isolated by crystallization as yellow crystals in 40% yield. The

'H-NMR shows a large downfield shift for the NH signal to 10.76 ppm, in agreement with

imine coordination. The "C-NMR spectra displays 3 CO signals at 220.1,2 13.7 and 2 1 1 -2 dong with îhe carbonyl-acyl signal a. 275.1 ppm, a typical value for a manganese-acyl carbonyl c a r b ~ n . ~ ~ ~ The stability of complex 45 is surptising considering that when N-

substituted imines 31a-c are employai, no tmce of the corresponding ql-coordinated acyl

complexes are deteetable by NMR This suggest an important steric infiuence on imhe coordination to the metal cenm with the smaIIer N-H subsbituted To~((CH~)~C)C=NH forming a more robust complex. Complex 45 undergoes orho-memtion when heated at 70°C for 20 hours in CH3CN (Eq. 3-10).

Complex 46 was isolated by rrcrystaüization fiom pentane affording 34% yield of light yellow crystals. Both 'H and 13C-NMR are consistent with the proposed structure.

3.1.3 CYCLOMANGANATION CHEMISTRY IN TE?E LITERATURE Cyclomanganation reactions using aIkyl manganese pentacarbonyl have been

extensively studied in the pas? and several complexes of the type 1, bearing a variety of donor atoms, have been prepared using this route (Fig. 13).

Kg. 13 General structure of ortho-mânganated species

In facf cyclometallation of manganese complexes was f k t noted with N-donor substrates, mainly by Bruce et al., who studied benzyl irnine~,~ aryl imines7 and azobenzened Complexes analogous to 430 and 43c have been prepared (47-48)', using N-subsîituted-beIlzalnimine instead of N-substitued-tolualnimine?

Despite the considerable amount of information conceming ortho-metallanon reactions with manganese carbonyl species, M e mechsnistic dam is available for this process. In a snidy covexing onhomanganation of azobenzene, Bruce proposedg a concerted

mechanism involving a-bond methathesis of the arene C-H bond with the Mn-alkyl bond

(Scheme 15).

Sêbeme 15. Proposed mechanian for azobenzene orthomanganation

This rnechanism is in good agreement with what is observed in our study. For example, when phenylmanganese pentacarbonyl is reacted with imines 31a-c (Eq. 3-8), almost 1 eqivalent of beozene formation is observed by 'H-NMR. On the other hand, when the same reaction is pedormed using methylmanganese penracarbonyl approximately 8% of acetaldehyde formation is observed by 'H-NMR (Eq. 3-11) (methane gas is

insoluble in acetonitrile and could not be quantitated).

The formation of a small amount of acetaldehyde could be indicative of a more complex mechanism. perhaps involving a formal oxidative addition/reductive eliminaton step. This would lead to a M n 0 intemiediate that could reductively eiim.hate one quivalent of acetaldehyde dong with me oaho-metallated product The two possible mechankms are outlined in Scheme 16. It should be noted that acetaldehyde could also arise

fkom a-bond metathesis directly with the acyl ligand. There is currently no mechanistic

information to discern between these possibilities.

Scheme 16 Two possible mechanism of orthometallation of ('ïol(li)C=DW) with (CO)5MnMe

'OLN H R'

(CO) &ln-Me t w)Wk 1 CH3

J--; Tol

"concerted a-bond

3.2 EFE'ECTS OF LEWIS AC= ON REACTIVITY OF AL- MANGANESE PENTACARBONYL WITEE IMINES 3.2.1 OB JECTLVES

The leaction of methyhanganese pentaarbonyl with amine, phosphine and atsine

ligands is weii known." The general &on is described in Scheme 17. First, the methyl group migrates to an adjacent CO7 followed by coordination of the incoming ligand L in the cîr position vacated by methyl ligand to give the acyl derivative (a). Secondly, slow ddonylat ion afford the substituted manganese-methyl complex B @).

Scheme 17. Reaction of lewis bases with methylmanganese pentacarbonyl

In light of the results presented in section 3.1. it c m be assumed that h i n e is acting as a Iigand (scheme 17) to form an acyl complex (A) thar deçarbonylates to generate the

corresponding alkyl complex (B). This alkyl complex then undergoes orthometallation to form the final product We reasoned that the reactivity of the system could be afEected by

changing the extent of the equilibrium (b). More precisely, by shifang the equilbrium towards the acyl complex (A), it is hoped that imine insertion into the Mn-acyl bond will be favoured over ortho-metallation of the Mn-alkyl bond

Many different techniques have been described in the fiterature in order to induce CO insertion into a Mn-aIkyl bond. For example, the rate of CO insertion in (CO),Mn-R is increased by a factor of IO4 wwben the reaction is perfonned in DMF instead of cyclohexylamine as the solvent." Also, Halpern" has shown that Ph,P=O catalyses the formation of the cwrdinatively unsaturated RCOMn(CO), species. Shriver and CO-worker reportedl* that strong Lewis acids (m, X = Cl, Br) have a profound effect on the kinetics and themodynamics of carbon monoxide insertions reactions. They observed thaî

alkylmangmese pentacarbonyl ream instantaneously with aluminium trihalide at room temperature to form an acyl complex stabilized by coordination to the Lewis acid and

formation of a stable metallocycle 49 (Eq. 3-12).

R = Me, CB2Ph X=Ci, Br 49

Interestingly, complex 49 was found to undergo m e r reaction with CO to generate the pentacarbonyl complex 50 (Eq. 3-13), even at subamiospheric CO pressure, while the parent complex RCOMn(CO),L (L = solvent) require relatively high CO pressure

to carbonylate at a simiificant rate. The net result is the displacement of a weakly coordinate halide ligand by a carbonyl ligand.

( O 5 atm.)

In a subsequent kinetic study, Basolo and Shriver" demonstrated that the Lewis acid not only stabrlizes the CO insertion product, bat also faditates the aIkyl migration by stabilin'ng the transition state of the alkyl migration step (Scheme 18). The rate of the reaction, when compared to the corresponding experiments without Lewis acid, increased by a factor of IO8!

Scheme 18. AIkyl migration mediated by molecuiar lewis acid AIX3

This intereshg behaviour prompted us to study the reactivity of lewis acids in our s~stern.'~ Namely, could aluminium hali& induce miine inseriion into the Mn-acyl of (CO),MnCOCH, over the orîho-rnetallation reactioa

3.2.2 REACTION OF (CO),MnR (R=Me,Ph) WITH Tol(H)C=NR' (Re=Me,Bz,Ph) IN PRESENCE OF AlCl,. 3.2.2.1 (CO),Mn- CH, REACTIVITY

The reactivity of methyhanganese pentacarbonyl and imines Tol(H)C=NR1 (R1= Me,Bz,Ph) has been investigated in the presence of AK13. The reaction of stoichiometrïc amounts of (CO),Mn-Me, N-methyl-tolualnimine 31a and aluminium trichloride in CD,CN

at room temperature for 24 hours does not lead to ortho-metallation Instead, a new complex is formed in 33% yield, that has been characterized to be the product of ïm.ïne

insertion into the Mn-acyl bond 51 (Eq. 3-14).

33% yield by NMR

The 'H-NMR for 51 shows resonances at 66.96 (dd, 4H, Tol), 5.09 (s, lH, Hl),

2.98 (s, 3H, Me,), 2.23 (s, 3H, Me), 2.05 (s, 3H, Tol-Me). These values are in good agreement with the expected chernical shift for imine reduction and amide formation.26 In addition, the observed chemical shifts are analogous to those of the isoelectronic Pd

complexes 34a

Aüempts to isolaîe 51 were unsuccesshil, however a phosphine derivative of mis

compound could be prepared and isolated. Addition of PPh, to a CD3CN solution of 5 1

reSults in immediate effemescence, due to CO loss, and the quantitative conversion of 51 to

the phosphine substituted complexe 52 (Eq. 3-15). The latter can be isohted in 22% yield by recrystallization at -30°C. Cornplex 52 was characte- by NMR, IR and elementai

analysls. The 'H-NMR for 52 in C,D, show resonances at 67.69 (m, 8H, aromatic), 6.99

(m, l lH, aromatic), 4.60 (d, ' ~ ~ - ~ 1 8 . 5 Hz, lH, Hl), 2.22 (s, 3H, Me,), 1.84 (s, 3H, Me) and 1.09 (S. 3& Tol-CH3). The doublet observed for Hl proton is consistent with substitution of one CO ligand by triphenylphosphine. The coupling constant of 3 ~ p - E = 18.5 Hz is large relative to what has been reponed previously in the literature." For example, 'J,, for the cornplex cis-(PPhJ(CO)&nCZE, was found to be 7.6 Hz.

51

(prepared in situ)

52

(quantitative yield)

The "P-NMR spectra of 52 shows a resonance at 653.98 ppm, representing a large

downfïeld shift when compared to fke PPh, in solution (-4.8ppm) and comistent with coordination of the phosphorus to the metai centre. 'Ihe structure of complex 52 was confimied by x-ray crystal structure of a close derivative. This topic wiU be covered in detail in section 3.4.1-3,

It is interesting to note that in the reaction describeci in Eq. 3-14, no trace of the corresponding ortho-metallation product can be detected by NMR. This implies that the

reactivity of the system has been changed completely and the presence of lewis acid (AlQ) in favour imine insertion over ortho-metallation, Further study is required to elucidate the

unique role of lewis acid in the promotion of im.ine insertion, but we propose that AlC13 stabilizes both the Mn-acyl ligand towards CO loss, and the transition state for irnine insertion (Scheme 19).

Scheme 19. Postulated role of AlC13 in imine insertion

Without Lewis Acid

C-H activation

- - "fast"

With Lewis Acid

2) Lewis acid muid t

stabilize transition state

The reactivity of imines Tol(H)C=N-CKPh and Tol(H)C=NPh with

methylmanganese pentacarbonyl and A1Q, has also been investigated (Eq. 3- 16). While

once again there is no evidence for imine ortho-metallation when AlCl, is present, these

reactions yield linle if any insertion products, and lead predominantly to decomposition. In the case of Tol(H)C=NC&.Fh, a compound preliminarly charactexised as 13 has been fonned in 12% yield,

12% yield by NMR

The presence of 53 is only speculative at mis stage, with the structure being assign solely on the basis of in sine 'H-NMR. The observed chemical shift for H, is 5.2 1 ppm and the benzylic proton display a characteristic diastereotopic pattern (5.85, d, 4J = 16 EIZ; 4.3 1,

d, 'J = 16 Hi). The isoelectronic Pd complex 34b shows simiiar chemical shift for the

reduced N-benzyl-tolualnimine signal ( 3: 5.03, s, 1H; 6H benzyl: 4.47, d, 1& 4~ = 16

Hi; 4.06, d, lH, 'J = 16 Hz ). Aaempts to isolate complex 53 or its triphenylphosphine derivatives have not been successful.

The reasons for the decomposition observed upon attempted insertion of Tol(H)C=NCwh and Tol(H)C=NPh are unclear. Analogous metalIocycles to those expected from these reactiom have been prepared using a different route (vide iofra) and were stable when heated in the presence of aluminium trichloride. Therefore, it is udüely that this arise fkom decomposition of the imine insertion product (e.g 53).

3.2.2.2 (CO),Mn-Ph REACTNITY When equimolar amount of phenylmanganese pentacarbonyl, imine 31a-c and

aluminium trichhide are nxcted in CD,CN at 70T for 2 days, the corresponding ortho- rnetaïiation product 43a-c are formed dong with approximately 1 equivalent of benzene (Eq. 3-17).

28-66% yield by NMR

The yield of the or&-metallation products are relafively small when compared to the corresponding reaction without and the NMR spectra contains several irnpurities due to side reactions or decomposition. However, no signals in the NMR spectra correspond to the imine insertion product Thus, mlike methylmanganese pentacarbonyl, addition of aliiminium trichloride to a mixture of phenylmanganese pentacarbonyl and imine is inefféctive in promoting imincl insertion over ortho-metaflation, To account for this clifference, we propose that the interaction of with the acetyl group is more stable then with the less basic b e m y l ligand. This provides l e s opportunity to pertmb the reactivity of (CO),MnPh fkom oaho-metallation.

3.2.3 CONCLUSION While the reaction of (CO),Mn-R (R=Me,Ph) with irnine Tol(H)C=NR'

(R'=Me,Bz,Ph) l a d s to the formation of an ortho-metallation products, the addition of one equïvalent oflewis acid (A1Ci.J to the reaction of (CO),MnCH, and Tol@)C=NCH,, l a d s to the formation of the novel product of imine insertion 5 1. This complex represents the first example of an imine insertion into a Mn-acyl bond, and only the second example of an imine insertion into a late metalcarbon bond. The unique role of in the reaction is not cleaidy understood, but a plausible hypothesis would be that it favors CO insertion and

stabilizes the transition state for the imine insertion step (Scheme 19).

3.3 (CO),Mn- ADDITION REACTION TO N-a-CHLOROALKYLAMIDE

3.3.1 OBJECTIVES The products of sequential CO and imine insertion into (CO)*-C& (5 1, 53) can

be synthesised fiom the reaction of methylmanganese pentacarbonyl, imines Tol(H)C=NRf (R'=Me,Bz) and A l S (Eq. 3-18).

51: R=Me (33% yield) 53: R=Bz (1296 yield)

However, this method is limited to the specific substrates mentioned, and the yield

of 51 and 5 3 are poor. Complexes of this type are important because they represents possible intermediates in imine/CO CO-polymerization, Thus, studying their structures and reactivity would be of interest. For this reason, a more general route for the synthesis of these compounds was examined. The possibility of using a metal carbonyl anion along with

N-a-chloroalkylamide to directly generate the products of sequential CO/imine insertion has

akeady been mentioned in section 2.2.1 (Eq. 2-10), Thus, addition of manganate carbonyl

anion to N-cc-chloroaikylamide should, in principle, Iead to the formation of the imine

insertion product (Eq. 3-19) as a more general synthesis of such compounds.

3.3.2 REACTIONS OF (CO),Mn-Na+ AND N-a-CHLOROALKYLAMIDES

3.3.2.1 REACTWITY

The reaction of sodium manganese pentacarbonyl'' with N-a-chloroaikyIamide

36a-c in CH,CN at room temperature leads to the immediate formation of the new

complexes 54-56 in good yields (Eq. 3-20). However, rather than the anticipated 5 membered metallocycle (in andogy to 51 and 53), these molecules were found to be the 6 membered metallocycles shown.

> 80% yield

Complexes 54-56 were isolat& by crystallisation in 52%, 48% and 39% yield,

respectively. The 'H-NMR of 54 shows resonances for the phenyl and tolyl group at 67.57

(m, 5H, Ph), 7.21 (d, J=8 Hz, 2H, Tol), 7.06(d, 1 = 8 Hz, 2H, Tol), as weii as 4.54 (s, lH, Hl), 3.16 (s, 3H, Me) and 2.32 (s, 3H, Tol-Me). The chemïcal shift observed for Hl in 14 is quite diagnostic, occuRng at 4.54 ppm, in good agreement with what is expected for a reduced imine. The 13c-IV~It spectra îs very Mcative of the shucaire of these

complexes. This shows a manganese-acyl signal at 6269.9pprn in 54, demonstrating that a

CO has undergone insertion into the M'-C(H)(ToI)-N(CE3J(COPh) bond (for comparaison, the "C-NMR resonance for the Mn-acyl signal of (CO)5Mn-C(0)-Me is 255.0 ppm2'). In addition, four distincts Mn-caTbOnyl signals are expected for 54 due to the chiral centre formed upon addition, causing differentiation of the two axial carbonyl

ligands (Fig. 14)- Four peaks were indeed observed, at 6218.1, 2 13.1, 212.2 and 2 10.1

ppm. Finaily, the amide carbonyl resonance appears at 6178.0ppm, compared to 617 1.9

ppm for the starting N-a-chloroakylamide 36a The observed downfield shift is similar to

that noted in 52, and consistent with the chelation of the amide oxygen to the metal centre." Complexes 55-56 show analogous spectral features.

axial carbonyl chiral center

Fig. 14 Stereochemical differenciation of axial CO ligand for 54

The formation of 54-56 upon addition of manganate pentacarbonyl ta N-a-

chloroalkylamide was at fïrst surprising. However, close examination of the reaction depicted in Eq. 3-20 suggest that the mechanism of formation of 5456 is relatively simple. The addition of (CO),Mn- to 36a-c is likely to proceed through formation of 57, as

outliaed is Scheme 20. It is weU known that alky1 manganese carbonyl complexes are in

equiiibrium with their acyl form (i-e. (CO)$h-C(0)-R), which can be trapped by a a-

donor ligand.10 Complexes 54-56 thus represent the product of CO insertion into the Mn-R of intemediate 58, which is then trapped by the amide oxygen in an intramolecular fashion

Scheme 20. Manganate addition to N-<~-cbloroaïkylami& 36a

3.3.2.2 LOW TEMPERATURE FORMATION OF 54

The reaction of (CO)5Mn-Na+ with N-a-chloroalkylamide 36a at low temperature

allowed the observation of complex 57 (Scheme 21). Sodium mangrnese pentacarbonyl and 36 were mixed as solids in a screw cap NMR tube and CD,CN was transferred into the

tube using vacuum transfer technique. The fkozen tube (stored in liquide NJ was then placed in the NMR probe cooled to -40°C. The temperature was kept constant until the

"solution" melted and made the first NMR acquisition possible (2-3 minutes). The temperature was then slowly increased and NMR spectra were recorded at -40, -35, -25 and -15OC (Fïg. 15).

At -40°C. the 'H-NMR specûa shows 2 signals in the 4-6 ppm region. ?he

monance at 64.56 ppm cornespond to H, signal of complex 54, while the peak at 65.94

ppm has k e n assigned to the H, signal of complex 57. Analogous signals for the N-Me (6

3.02) and Tolyl(6 2.35) are also obsemed for 57. Thus, the major species at -4û°C appears

to be the product of addition of (CO),&- to 36a, complex 57, and CO insertion into 57 is

relatively slow until above -lS°C. ?he intramolecular amide chelation appears O make the

CO insertion into the manganese-aIkyl bond a surprisingly facile process. For cornparison, CO insertion into the manganese-methyl bond of (CO),MnCH, under 1 atmosphere of carbon monoxide is only 75% completed at 2S°C after 24 honrs (Eq. 3-21)."

In addition, it is welï known that elecmn withdrawing subsnaients on the alkyI

group decrase the rate of carbonylation? For example, the rate of the carbonylation reaction described in Eq. 3-22 was found to be 100 times slower when R=Ph instead of R=H. Considering that complex 57 (Scheme 20) bears both aromatic and amide group substituents on the akyl, it is surprising to observe that carbonylation of 57 is almost completed at -lS°C in only a few minutes. Thus, intramolecuiar cheiation of the amide oxygen appears to greatly accelerate CO insertion,

3.3.2.3 STRUCTURAL CHARACTERISTICS OF 54

The proposed structure for complex 54-56 was confirmed by x-ray structurai characterization of 54, presented in Fig. 16. 'Ihe crystailographic data, including a l l bond lengths and bond angles, are enclosed in the appendix section. The stnicnire of 54

demonstrate that CO insertion (C(5)-O(5)) into the Mn-CH(Tol)-N(Me)(COPh) bond does indeed occur and also that the amide oxygen has chelated to metal centre to form a nearly planar six membered manganacycle.

H g 16. X-ray crystal structure for complex 54

Complex 54 shows a slightiy distorted octahedral geometry about manganese, with the axial C(4)-MnC(1) bond angle of 172.3(2)O. Distances fiom manganese to carbonyl carbon atoms are found to be Mn-C(l) = 1.854(5) Mn-C(3) = 1.860(5) and Mn-C(4) = 1.862(4) nK MnC(2) bond tram to the coordinated carbonyl oxygen, however, îs only 1.780(4) A and is accompanied by a slightiy longer C-O distance for the carbonyl

C(2)-0(2), 1.149(4) & than for the other carbonyls: C(1)-0(1), 1.128(4) C(3)-0(3), 1.136(5) A; C(4)-O(4). 1-13 l(4) This is attributed to x-electron donation Born oxygen to manganese, allowing greater rc-backbonding to the tram CO. This resuitts in a shortened

Mn-C bond and a lengthened C-O bond as observed. The same tram relationship is evident in other stnictures having a ketone oxygen chelated to mangane~e.~

Figure 17. Selected bond lengths (A) for complexe 54 six membered ring and the reference molemie fonnamide3' 59

Selected bond lengths for the six mernbed manganacycle are schematically represented in Figure 17. An interesting feature of complex 54 is the N(1)-C(7) bond length of 1.326(4) k This is shorter than what is expected for a typical ami& bond. For example, the C-N bond disiance in formamide (59) is 1.376 k In addition, the typical

bond length for carbon-nîtrogen double bond C=N is approximately 1.30K" This indicates a high degree of double bond character in the N(1)-C(7) amide bond In contrast, the ami& carbonyl bond length C(7)-O(6) was found to be significantly longer (1.259(4) A) then the

corresponding carbonyl of the reference formamide 59, wich has a C=O bond distance of 1.193 A These two observation are very indicative of a high degree of interaction between the amide ligand and the Mn centre. Thus, the complex 54 is best represented as king in resonance with 54' (Eq. 3-23).

A shnilar metallocycle with a chelated amide has been prepared with palladium and was presented in section 1.3 (Fig. 12). Borh C-N and C=O amide bond length are within

the experhental emor to what is observed for 54, with the metal-oxygen distance slightly shorter for the palladium system.

3.3.2.4 CONCLUSION The formation of complex 54 (and derivatives 55- 56) constinnes the fïm directly

observed example of CO insertion into a late metal-CH(R)-=OR) bond, representing one of the two propagation steps in imine/CO CO-polymerization (step 2, Eq. 3-24). The

unusual mild conditions required to insert CO into the intemediate Mn-R bond c m be explained by the stabibîtion of the CO insertion product through inaamolecular amide chelation. This represent m e r evidence of the viability of a imindC0 CO-polymerization process."

Finally, the synthesis of complexes 5456 by addition of a metallate carbonyl anion

to the elemophilic N-a-chloroaikylamide under very mild conditions suggest the porential

utility of this synthetic route for the general synthesis of complexes of this type.

3.4 REACTIVrrY OF 54 Complexes 54-56 constitute interesthg molecules since they represent

intexmediates in a potential imine/CO CO-polymerization process (Eq. 3-25). Thus, their

reactivity was investigaîed in order to obtain basic information concerning the reaction properties.

R' Tol

H Et' - (Eq. 3-25)

R H

54-56

3.4.1 DECARBONYLATION OF 54

3.4-1.1 REACTIVITY When heated at 500C for 15 minutes in acetoniüile solution, complex 54

decarbonylates to fonn the 5 membered metaiiocycle 60 in 40% yield by NMR, dong with a number of unidentifiecl decomposition products (Eq. 3-26).

ph 40% yidd by NMR

Complex 60 was isolated by pentane extraction as a yellow powder in 25% yield.

The 'H-NMR for 60 in C,D, shows resonances at 66.85-7.12 (m. 9H, aromatic), 5.04 (s,

lHy H,), 2.49 (s, 3H, N-Me) and 2.17 (s, 3H, Tol-Me). The '%-NMR spectra for 60

shows the four Mn-carbonyl signals at S220.8,214.8,212.8 and 212.2 ppm, as weU as the

disappearence of the Mn-acyl carbonyl signal of 54 (6269.9 ppm), confimiing that

decarbonylation has occured. The amide carbonyl resonance appears at 6179.2 ppm, in

good agreement with the proposed amide chelated structure.

3.4.1.2 REACTMTY OF 60 WITH PPh,

Similarly to what was observed with complex 51 (Eq. 3-15), the addition of triphenylphosphine to 60 was found to displace one carbonyl ligand, forming the

corresponding derivative 61 in almost quantitative yield (Eq. 3-27).

PPh 3

quantitative

61

Complex 61 was isolated by crystallization fkom acetonitrile as a yellow powder in

52% yield. The 'H-NMR spectra shows resonances at 67.77 (rn, 6H, aromatic), 7.22 (m,

3H, aromatic), 6.95 (m, lm, aromatic ), 4.59 (d, 'J,, = 18 hz, 1 H, Hl), 2.22 (s, 3H, N- Me) and 2.14 (s, 3H. ~ o l - ~ e ) , consistent with the proposed structure. 'Ibe coupling of Hl with phosphorus supports the ligand substitution reaction, i-e. replacement of one CO by

PPh,. The "P-NMR shows a signal at 655.57 ppm, close to what has been observed for

the analogous phosphine substituted complex 52 (Eq. 3-15>. The l3C-~h4Et spectra of 18

shows 3 inequivalent CO resonances ail of which are coupled to phosphorus: 6 226.8 (2Jp-,

= 84 hz); 220.6 CJ, = 146 hz); 217.9 (2~p, = 84 hz). The amide carbonyl chernical shift observed is at 178.1 ppm, in good agreement with the cheLated structure. The structure of complex 61 has been confkmed by x-ray structural characterization.

3.4.1.3 X-RAY STRUCTURAL DATA FOR 61 The structure of complex 61 has ken solved b y x-ray c~staïiography and is

presented in Fig. 18. The coordination geometry around the manganese atom is near- octahedral, with a C(4)-Mn(1)-O(4) bond angle of 80.12(7)0, smalIer than the

corresponding C(5)-Mn(1)-O(6) bond angle observed in the six-membered complex 5 4 (88.30(13)0). Similar bond angles have been reported for Mn complexes with analogous 5- membered ring having a Wone chelated to Mn centreY ' Ibe Mn-CO bond lengths were found to be very close to each others: Mn-C(l), 1.814(2) Mn-C(2), 1.775(2); Mn-C(3).

1.8 12(2) k This similariq is also observed for the three carbonyl bond lengths, with

almost identicai values oE C(1)-0(1), 1.149(2) C(2)-0(2), 1.155(2) C(3)-0(3), 1.154(2) These data's, dong with the observed Mn-P bond length of 2.3690(9) A, are similar to other phosphorus monosubstituted manganese tricarbonyl complexes previously

reported? The 5 mernbered manganacycle of complex 61 fom an extended planar system

with deviations* fiom the plane of less then 5.4(2)O.

Figure 1%. X-ray crystal structure of 61

As discussed in section 3.3.2.2, a sirnilar metallocycle has been smichirally characterized for the palladum system and was presented in section 1.3 (Fig. 12). Except

for the metai centre, the metallocycle backbone is almost identicaï for both complexes. Ibe

relevant bond lengths are compared in table 3.

M M-C C-N N-C(0) C a M-O

a i ( p p h 3 ) ( c o ) ~ 2.128(2) 1.482(2) 1:313(2) 1.270(-(14)

n

Table 3. Bond lengths (A) of backbone metallocycle for complex 61 and 34b

The data presented in the above table indicates a strong similarity between the two metallocycles, with short N-C(0) bond and long amide carbonyl (C=O) bond, indicative of a bigh degree of delocalization between the amide bond and the metal centre, In a similar manner to what has been proposed for 54 (Eq. 3-23), the cornptex 6 1 can be regarded to be in resonance with structure 61' (Eq. 3-28).

3.4.1.4 REACTZVLTY OF 60 WITH CO

The thermodynamic stability of palladium complex 34b (section 3.1) was postulated" to prevent m e r insertion of CO and imine into the Pd-alkyl bond. Simiiarly, when a CDFN solution of 60 is plxed under 1 0 psi of carbon monoxide at room temperature for 24 hours, liberation of CO and immediate 'H-NMR shows no aace of 5 4

(Eq. 3-29). The 5 membered chelated Ling in 60 thus appears to be significantly more stable than 54.

3.4.2 REACTIONS OF 54 WITH TRIPHENYLPHOSPHINE As discussed before, complex 54 represents a potential intermediate in an imindCO

CO-polymerization process, and the next step in this reaction would be the opening of the cbelated ring to allow coordination of an incoming substratte. lh order to observe the opened structure, tciphenylphosphine was employed as a potential trapping agent.

The reaction of 54 with one equivalent of Cnphenylphosphine in acetonitrile at OOC for 2 hours &ts in the formation of the new complex 62 in approximately 70% yield by NMR (Eq. 3-30). This complex has been characterized as the product of de-chelation of the amide by PPh.

The complex 62 was ïsolated in 40% yield as a pale yellow so~id.~' The 'H-Nh4R of 62 in C,D, show a series of multiplets in the ammatic region correspondhg to 25H,

dong with two singlets at 6 = 2.53 ppm ( 3 8 N-Me) and 2.02 ppm (3H. Tol-Me). The

peak for H, proton is lost in the aromatic region, with an integrated intensity of 25 (24

aromatic hydrogen in 62). The 3LP-NMR spectra shows a resonance at 652.05 ppm,

demonstrating the coordination of PPh, to the Mn centre. Whïle smtable crysrals for x-ray charactenization could not be obtained, the "C-NMR provides strong evidence for the

proposed structure of 62 (Fig. 19).

ti lH= t.02

Fig 19 NMR spectroscopie data for 62

First, a manganese-acyl signal can be detected as a doublet at 6 267.5 ppm ('J,, =

50 Hz), and is indicative that CO de-insertion has not occurred duMg the reaction. A~so, a series of four doublets, corresponding to the four Mn-CO ligands, is present in the carbonyl

region at: 6 216.9 ( ? J ~ ~ = 32 Hz); 216.2 = 84 Hz); 214.6 (2~P-C = 76 HZ); 213.2 ('J~-=

= 59 Eh). This supports the asswnption that ûiphenylphosphine substituted the chelated amide rather than a carbonyl ligand. Further evidence of the latter can be fowd in the

chernical shift of the amide carbonyl peak, observed at 170.8 ppm. It has b e n shown previously that manganese complexes havùig a chelated amide to the metal centre (54,6 0, 61) all exhibit a 13C amide carbonyl signal af 178-180 ppm. In contrast, a non-coordùiated amide oxygen like for the reference compound N-disubstituted-bende (RC(O)N(EX)CH$?h) generally display the same resonance at 4 7 1 ppm? Thus, the amide

group in complex 62 is not chelated to the metal centre and results in the proposed open structure. The extremely mild conditions ( O r ) required to open the chelated ring in 54 is surprising when compared to the exceptional stability associated with the corresponding 5

membered ring in 60. Indeed, PPh, displace a carbon monoxide ligand in 60 rather than opening amide chelation (Eq. 3-3 1).

The formation of complex 62 implies there is an easiiy accessible coordination site

for intermediate of type 54, a primary condition for fuaher insertion reactions.

3.4.3 REACTIVITY OF 54 WITH Tol(H)C=NCH, 3.4.3.1 REACT)[ON OF 54 WITH Tol(H)C=NCH,

The results in 3.4.2 suggest that imine could also bind to Mn centre of 14 to form a de-chelated complex quivalent to 62 (Eq. 3-32).

For this reason, the reaction of 54 with Tol(H)C=NCH, was investigated. EQuimolar amounts of 54 and Tol(H)C=NCH, were dissolved in CD3CN and the reaction was foilowed by 'H-NMR (Eq. 3-33).

The NMR spectra for reaction 3-33 show the slow decart>onylation of 54 to form 60 and the reaction was completed after 24 hours. Exactly one equivaient of imine is recovered, indicaiing that Tol(H)C=NMe is unreactive towards complex 54 under these reaction conditions. In a similar manner to what has been observed for the simple decacbonylation reaction (Eq. 3-26), the reaction is not clean and sigdicant amounts of unidentified decomposition products are observed. Thus it appears that ToloC=NMe is not a sufficiently stmng ligand to generate a stable de-chelated product of 54.

3.4.3.2 REACTIONS OF 54 AND Tol(E)C=NMe WITH AICI, A) REACTION OF 54 AND Tol(H)C=NMe WITH AICI,

The presence of aluminium aichloride was shown U> favour imine insertion into Mn-acyl bond over ortho-metallation reaction, A Smilar behaviour with 54 would be of interest as th& would lead to the formation of a dipeptide backbone. Thus, equimolar

amounts of complex 54, Tol(H)C=NMe and aluminium aichloride were reaçted in CD,CN and the reaction was followed b y NMR After 10 minutes, several new species are fomed,

including irnine 'H-NMR peaks 16 9.30 (s, lH, - C = ) , 6 3.85 (s, 3H, N-Me)], shifted

sisnificantly downfield of free imine [68.25 (s, H-C=), 6 3.41 (s, NMe)], corresponding to

an ql-cwrdinated b i n e complex. Importantly, these peaks do not correspond to the

chemical shift observed for the imine/AïCi, adduct Tol(H)C=NMe+AlC&- (63), whose

signai in CD3CN are 6 8.79 (s @r), 1 8 H,) and 6 3.56 (s @r), 3H, Me). However, this

product decomposes rapidly over a period of 1 hour to fonn a complex mixture of unknown products. The situation is different when two equivalent of Al(& are used (Eq. 3-34). Reaction of 54 and Tol(H)C=NMe with 2 equiv. of AlQ3 ieads to the formation of a new product (64).

> 90% yield by NMR

Complex 6 4 has been tentatively characterized by 'H-NMR to be the structure

shown. The 'H-NMR of 64 shows resonances at: 6 9.13 ppm (s, lH, Ha), 7.60-7.90 (m,

1331, 5.69 ppm 6, 1H, H,). 3.84 ppm (s, 3H, Mea), 2.45 ppm (s, 3H, MeJ, 2.35 (s, 3H, Tol), 2.32 (s, 3H, Tol). The downfïeld shift observed for imine peaks at 9.13 and

3.84 ppm, with 1:3 hydrogen ratio, are very indicative of a ql-coordinated imine to

manganese, whde the H, peak at 6 5.69 demonstrates the existence of the amide ligand.

Formulation of structure of complex 64 is onïy hypothetical at this stage, and preliniinary attempts to isolate this complex have not been succedul.

B) REACTIVITY OF COMPLEX 64

When the reaction 3-34 is followed over a period of 24 hours a . room temperature, the postulated infermediate 64 slowly reacts to give a complex mixture of unidentifed products. An interesthg feature of that reaction is the formation of a set of two doublets x 6.03 and 4.59 ppm showing fine diastereotopic coupling of J = 4.2 Hz. This supports the formation of an orgaoic product having 2 chual centres in the molecule, and suggest m e r exploratory reactions of complex in the future would be of interest 3.5 lMINE/CO CO-POLYMERIZATION EXPERIMENTS

3.5.1 OBJECTFVES As discussed previously, it is known that ;tlkylmanganese pentacarbonyl are in

equilibrium with their CO insertion product (Le. acyl).1° For the equilibnum described in Eq. 3-36, it has been postulated (Scheme 19) mat presence of Lewis acid stabilize the acyl complex 65 and drive the imine insertion reaction over the ortho-metaliation

Tol H

(Eq. 3-35)

Another possible way to shift the equilibrium toward the acyl complex 65 would be to perform the reaction under high CO pre~sure.~' Thus, it is hoped that by stabilizing the

acyl complex 65 under high CO pressure, the xeactïon of h i n e insertion into the Mn-acyl bond will be favoured over ortho-metallation, Similar behaviour for complex 51 (Eq. 3-35) and m e r reaction with imine would lead to imine/CO CO-polymerization. This was explored as described below.

3.5.2 REACTION OF (CO),Mn-Me WITH Tol(H)C=NMe MethyImanganese pentacarbonyl (20.0 mg, 0.1 mmoI) was reacted with excess of

Tol(H)C=NMe (750.0 mg, 5.6 mmol) under 600 psi of carbon monoxide at 7 0 T for 14 hours (Eq- 3-36). The excess imine was then removed under high vacuum (50 mtorr @

Sû°C) and the midue examinai by 'H-NMR This shows the presence of approximately 20% yield of the ortho-metallard product 43a, dong with complex decomposition. A

control reaction of 43a with Tol(H)C=NMe tmder 600 psi CO shows the slow formation of similar decomposition products to those above, suggesting they arise fkom 43a, not imine insertion (Eq. 3-37).

M e CO, 600 psi

(COkMn-Me + H Me

excess

431

(= 2Wo yield by NMR)

3.5.3 REACTION OF (CO),Mh-Me WlTa Tol(H)C=NMe IN PRESENCE OF AICI,

Aliiminium hichloride was shown to promote imine insertion over ortho-metallation when (CO)5Mn-Me was reacted with TolOC=NMe. Thus, methyl manganese pentacarbonyl (20.0 mg, 0.1 mmoles), AIQ, (13.0 mg, 0.1 mrnoles) and excess Tol(H)C=NMe (750.0 mg, 5.6 mmoles) were reacted in 5 ml of CH,CN under 600 psi of CO at 70OC for 16 hours (Eq. 3-38). Tbe excess imine was removed under high vacuum (50 mtorr @ 50°C) and the residue examined by 'H-NMR.

43a 51

(= 10% yield by NMR) "nace"

This shows the presence of the ortho-metallation product 43a in approxirnately 10

% yield, and decomposition product similar to what is observed for the reaction 3-36- Only a trace amount of the imine insertion product can be detected.

3.5.4 CONCLUSION Preliminary attempts to utilize high pressure of carbon monoxide to induce the co-

polymerization of Tol(H)C=NMe and CO with alkylmanganese carbonyl has not been successful. Tbe preferential formation of the orth~metallation product was observed, and Al% was found to be inactive to induce imine insertion under these conditions. It should be noted, however, that imine is in equili'brium with the coordination product Tol(H)C=NMe+Alci,- 63 in acetonitrile solution (Eq. 3-39). Thus, when a large excess of imine is present, the equilibrium is shifted toward complex 63, which likely completely inhibits the activity of AQ. This, as welï as the sensitivity to exact reaction conditions found in the stoichiometric experiments, suggests future studies should be directed towards examining the effect of various Lewis acids, miine substituents, and other reacîion variable on the potential use of manganese carbonyl catalysts on imine/CO CO-polyrnerization.

3.6 GENERAL CONCLUSION These studies have demomtrated that the sequential insertion of CO and imine into

the manganese-methyl bond of (CO),MnMe can indeed be achieved While it was found that the reaction of (CO),Mn-R (R = Me, Ph) with Tol(H)C=NR' (R' = Me, Bz, Ph) leads

to ortho-metallation products 43a-c (Eq. 3-40), the addition of AICI, to the reaction of

(CO)sMnCH,

CD3CN, 70°C ")=. (1 -5 ciays) (CO)--R + - (Eq. 340) H

\ R' -Eu3

with Tol(H)C=NMe results in the sequential insertion of CO and imine into the M m e bond (Eq. 3-41). This constitutes the fim example of an imine insertion into a Mn-acyl bond, and also one of the few examples of an irnine insertion into any late metal-carbon bond. The unprecedented role of AlC4 in this reaction remaius unclear. However, coordination of the latter to the acyI ligand in (CO),Mn(COMe) is postuiated to account for the observed ceactivity (Scheme 19).

Complexes sunilar to imine/CO insertion products (54-56) can also be prepared by

addition to N-a-chloro~larnide substrates, and have allowed the chemistry of

these complexes to be explored under more mild conditions. C o n s i d e ~ g the reaction depicted in scheme 22, this shows that un&r kinetic conu5riom , CO inserts into the meîal- R bond of complex 57, and the product of insertion (58) is stabiiized by intramolecular

amide chelation. In addition, addîng a a-donor ligand (PPhJ to a solution of 54 leads to the

formation of the de-chelated complex 62 under extremely mild conditions, showing that

there is an easily accessible coordination site on 54, an important condition for the eventual extension of this chemistry to CO/imine CO-polymerization,

Scheme 2û. Synthesis of 54 and reactivity with Pm

The reactivity of 54 has demonstrateci, however, that the de-insertion of CO generates a very robust 5-membered metallocycle, thaî is inert towards re-insertion of CO (Eq. 3-42). This suggest thai our orig.mil hypothesis, that the neutral Mn centxe in 60

would allow subsequent CO insertion, is not correct. Instead? the results shown in this

thesis demonstrate that, in order to achieve an imine/CO CO-polymerization, conditions must be found in which imine insert into 58 prior to conversion to the 5-membered metallocycle. This should be the focus of the research in this area.

References

(1) (a) DeShong, P.; Sidler, D.R.; Rybczynski, P.J.; Slough, G. A; Rheingold, A.L. L A m Chem Soc , 1988, 1 10, 2575-2585 (and references therein). @) See ref 1, chapter

1.

(2) Calderazzo, F. Angew. Chem, In?-EdEngL 1977, 16, 299. (B) Novak, K.; Calderazzo, F. J. Organomet. Chem 1967, 10, 101.

(3) (a) Flood, T.C. In Topics in 0rgmCPLIc mid Orgamltzerallc StereochemIfUstry; Goefioy, G.L., Ed.; Vol. 12 of Topics in Stereochemistry; Wiley: New-York, 1981, 12,

83. (b) Flood, TC; Jensen, J.E.; Statler, J A J.Am.Chem.Soc. 1981, 103, 4410.

(4) (a) DeShong, P.; Slough, GA.; Rheingold, A.L. Tetrahedron Letfers, 1987, 28,

no 20, pp. 2229-2232. (b) DeShong, P.; Slough, G.A. Orgmmetallics, 1984, 3, 636- 638. (c) Booth, B.L.; Gardner, M.; Haszeldine, RN. J. Chem Soc., Dalton Trans.,

1975, p. 1856. (d) DeShong, P.; Slough, G.A. Tetrahedron Letters, 1987, 28, no 20,

pp. 2233-2236-

(5) Dinger, M.B.; Lyndsay, M.; Nicholson, B.K. Journal of Orga~meiiallic

Chemktry, WB, 565, 125-134, and references cited therein.

(6) Bennet, R.L.; Bruce, M.I.; Matsuda, 1. Aust. J. Chem 1975, 28, 1265-72.

(7) Bennet, RL; Bruce, Ml.; Goodall, B.L.; Iqbal, M Z ; Stone, F.G.A. J. Chem.

Soc-, Dalton Trms., 1972, 1787.

(8) Bruce, M.I.; Goodall, B.L.; Stone, F.G.A. J. Chem Soc., Dalton Trans., 1978,

697

(9) Bemet, RL.; Bruce, M.I.; Gordon, F. Journal of Organomet. Chem, 1975, 94,

65-74.

(10) Kraihanzel, CS.; Maples, P.K. Inorganic Chemistry, 1968, vol 7, no 9, p. 1807. (And references therein).

(1 1) Mawby, R.J.; Basolo, F.; Pearson, R.G- J. A m Chen Soc. 1964, 86, 3994.

(12) Darensbourg, D.J.; Wolker, N.; Darembourg, M.Y. J . A m Chem Soc. 1980, 102, 1213.

(1 3) Webb, S.L.; Giamdomenico, C M ; Haipem, J. J. Am. Chem Soc. 1986, 108, 345-

(14) (a) Butts, S-B.; Strauss, S-H-; Holt, E.M.; Strimson, RE.; Aicock, N.W.;

Shriver, D I . J. A m Chem Soc. 1980, 102, 5093-5100. (b) Butts, S.B.; Holt, E.M.;

Strauss, S.H.; Alcock, N.W.; Strimson, RE.; Shnver, D.F. J. A m Chem Soc. 1979,

101, 5864-5866.

(15) Richmond, T.G.; Basolo, F.; Shrïver, D.F. Inorg. Chem 1982, 21, 1272-1273.

(16) The reaction of aikyhanganese pentacarbonyl with imines described in eq. 3-3 have

been eied in DMF as the solvent and also with iriphenylphosphine oxide as the CO-catalyst, but no significant change in the reaction has been observed-

(17) See reference 21, chapter 1.

(18) Prepared using literature procedore: Hemnannl'rauer, Synthetic methoak of orgmiometallic and Inorganic Chemistry, V-7, pt. 1, Srmgart, New-York, 1996.

(19) (a) Calderazzo, F. Angew. Chem Int. Ed Engl. 1977, 16, 299-3 11. @)

Wojcicki, A. Adv. Orgrnomet- Chem 1973, 11, 87-145.

(20) Methyhangmese pentacarbonyl (27mg, 0.12mmol) was dissolved in 1 ml of CDJN and the solution was placed in a screw cap NMR tube under 1 atmosphere of CO.

The reaction was foiiowed by NMR

(21) Cawsc, J.N.; Fiato, RA.; Pruett, R.L. Journal of Organ~metdc Chemistry,

1979, 172, 405-413.

(22) Rnobler, C.B.; Crawford, S.S.; Kaesz, B.D. Inorganic Chemistry, 1975, vol 14, no 9, p. 2062.

(23) Sando*, C. Tize Chemistry of rhe Carbon-Nitrogen Double-Bond; Pataî, S., Ed.; Wiley: New-York, 1970; p-1.

(24) (a) Huie, B .T. ; Knobler, C.B. ; Firestein, G. ; McKinney, R. J.; Kaesz, H.D. J. A m Chem Soc. 1977, 23, 7852-7862. (b) Huie, B-T,; Knobler, C.B.; McKinney, R.J.; Kaesz, H.D. J , Am Chem. Soc. 1977, 23, 7862-7870.

(25) The maximum torsion angle observed within the 5 membered manganacycle is - 5.4(2)' for C(5)-N(1)-C(4)-Mn(1).

(26) Silverstein, R.M-; Bassler, G.C.; M o a TC. Spectrometn-c Identîjïcation of Organic Compounds, fZFh edition, John Wiley & Sons, Inc., New-York, 199 1, p. 246.

(27) Similar resulta have been observed by proton NMR for 16b-c, but complexes 19b-c were not isolated.

(28) (a) Lindnen, E.; Starg, K A ; Eberle, W.H. Chem. Ber. 1983, 116, 1209-1218.

(b) Kraihaazel, C S ; Maples, P.K. Imrgmic CheNstry. 1968, vol 7, no 9, 1806.

(29) Darst, KP.; Lukehart, CM. Journal of 0rganomet.Chem 1978,161, 1-11.

(30) (a) Paz-Sandorval, MA; Saavedra, P.J.; Joseph-Nathon, P. OtgmmefaZlics, 1992, 11, 2467-2475- (b) Hemnan, W.&; Andrejewski, D.; Hardtweck, E. J o u d of Organomet. Chem 1987, 183-195. (c) Paz-Sandorval, MA; Powell, P. Urgm~7me&dIics, 1984, 3, 1026-1033. (d) Bodner, G.M. Inorgrmic C h e m i s ~ , 1974, Vol. 13, no. 11,

2563.

(31) Ref. 27,chap. 1.

(32) Ref. 15, chap. 2

Experimental section

1, General

'H, "C, and "P NMR were recorded on JEOL-270, Varian XL-200 and Varian

XL-300 spectrometers. Chemical shifts are reported in parts per million (6) downfield form

tetramethylsilane as an interna1 standard. Coupling constants (J values) are given in hertz

(Hz), and spin multipficity's are indicated as follow: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet). Infkared spectra were recorded on a Bruker IFS-48 spectrometer. Peak position are given in reciprocal centimetres (cm-') and are listed as very strong (vs), strong (s), medium (m), or weak (w). X-ray analyses were obtained on either an Enraf-

Nonius CAD4 with CuK a radiation or a Rigaku diffractometer with a MoK a radiation.

Elernental analysis were performed by Laboratoire d'analyse elementaire de 1'Universite de

Montreal, Montreal, Quebec, or by QTI Quantitative Technologies Inc., Whittehouse, NJ.

Ethyl ether, benzene, and tetrahydrofuran (THF) were distillai from sodium/benzophenone ketyl under nitrogen. Acetonitnle and pmtane were distilleci from CaEE, under nitrogen. Benzene-d, was vacuum m e r r e d fiom sodium/benzophenone and acetoniûile-d, was vacuum ûamferred from CaH,. AIl NMR solvents were stored under nitrogen over 3A molecular sieves.

Reactions were perfoxmed either in a dry-box under a niuogen atmosphere or using standard Schlenk techniques. The high-pressure apparatus (Parr, mode1 4842) consisted of a stainless steel reactor and pressures were determiued directly fkom a gauge attached to the

autoclave.

Cobalt and manganese carbonyl were obtained fkom Strem Chemical Co. (Catalog No. 27-0400 and 25-1330, respectively) and were used without m e r purification. Carbon monoxide (99.9946) was purchased from Matheson and used as received. NaCo(CO),,' NaCo(CO),(PPh3),2 (CO)$In-R (R = Me, Ph),' ~ a M n ( C 0 ) ~ ~ and N- substituted tolualdimine Tol(H)C=NR (R = Me, Bz, ph)' were al1 prepared using literature procedure. AU other reagents were purchased f o m Aldrich and used as received.

2. General procedure for the hi@-pressure CO reactïons The reaction mixture was prepared inside the dry-box and placed into the reactor,

which is sealed under a nitrogen atmosphere. The high-pressure reactor was then presswized with CO prior heating. After cornpletion of the reaction, the reaction mixture

was depressurized, and the residue collected inside the dry-box, under N, atmosphere, before work-up .

3. General procedure for NMR experiments NMR spectra of air sensitive materials were recorded using a screw cap NMR tube

(FEE Teflon valve) or a flame s d e d tube. The followhg conditions for the monitoring have been employed: 'H: 4 0 mg of product was used (pulse angle, 45'; relaxation delay, 1s; scans, 8). "P : -50 mg of product was used (pulse angle, 45'; relaxation delay, 2s; scans, 100). '%: 4 0 mg of product was used (pulse angle, 30'; reIaxation delay, 1s; scans, 2000). 13C-NMR of complexes 43a-c, 45, 46, 54, 60-62 were recorded in C,D, at 5" with modifiai parameters: pulse angle, 3S0; relaxation delay, Os- These conditions

were found to significantly decrease the relaxation time of carbonyl carbon, allowing the observation of all peaks in each case.

4. Experimental details

Synthesis of Tol(H)CN(Me)COPh+Cl- (36a) Benzoyl chlonde (1.06 g, 7 -5 mmol) and Tol(H)C=NMe (1 .O0 g, 7.5 mmol) are

dissolved in 20 ml of acetonitrile and the solution is stirred at room temperature for 30 minutes. The solution is concentrated by vacuum und first appearance of a solid and piaced at -30°C overnight The white crystalline product is collected by filtration, washed with cold

ether and dried under vacuum. (934.0 mg, 45% yield). 'H-NMR (CDQV): 6 7.45-7 -55

(m, 5H, Ph), 7.44 (d, JH-H = 8.4 Hz, 2H, Tol), 7.26 (d, JH-= = 8.2 hz, 2H, Tol), 2.76 (s,

3H, N-Me), 2.36 (s, 3H, Tol-Me). 1 3 ~ - ~ ~ ~ (CDFN): 6 171.9, 139.1, 135.3, 133.9,

130.4, 129.3, 128.7, 127.2, 126.9, 76.7, 29.7, 20.1.

A similar procedure to the synthesis of 36a was followed with Tol(H)C=NCH2Ph

to yield 0.906 g of 36b (54% yield). 'H-NMR (CD3CN): 6 7.57-7.64 (m, 2H), 7 -48-7.54

(m, 2H), 7.41 (d, JH-= = 8.2 Hz, 2H), 7.31 (s, lH), 7.11-7.21 (m, SH), 7.02-7.09 (m,

2H), 4.55 (s, ZH, -C&Ph), 2.29 (s, 38, Tol-CH,). 13c-~h4R (CD3CN): 6 172.4, 139.3,

137.6, 135.4, 133.7, 130.5, 129.1, 128.9, 128.0, 127.6, 127.2, 126.7, 78.1, 46.4, 20.2.

Synthesis of Tol(H)CN(Ph)COMe+Cl- (36c)

Acetyl chloride (100 pL, 1.41 m o l ) and Tol(H)C=NPh (280.0 mg, 1.41 mmol) are dissolved in 5 ml of ether and the solution is stirred at room temperature for 5 minutes. The solution is placed at -30°C ovemight. The white crysr;illine product is collecteci by

filtration, washed with cold ether and dried under vacuum. (325.0 mg, 85% yield). 'H-

NMR (CD,CN): 6 7.87 (s, lH, Tol(CL)CEE-N), 7.31 (m, 33, pH), 7.03 (dd, 4H, Tol),

2.25 (s, 3H7 Tol-a , ) , 1.78 (s, 3H, CH3-C(0)-).

Synthesis of Tol(H)PPh,CN(Me)(C O'Bu)+Cl- (38)

Trimethyl acetyl chloride (241.0,2.0 m o l ) , Tol(H)C=NMe (266.0 mg, 2.0 m o l ) and triphenylphosphine (525.0 mg, 2.0 m o l ) are dissolved in 5 ml of ether and the solution is stin-ed at room temperature for 2 hours. The solution is placed at -30'32 ovemight, and the white powder is coUected by filtration, washed with cold ether and drïed

under vacuum. (557.0 mg, 54% yield). 'H-NMR (CD,CN): 6 7.63-7.75 (m, 9H, PPh,),

7.51 (m, 6H, PPh,), 7.12 (d, J = 8.1 Hz, 2H, Tol), 7.00 (dd, J = 8.1 Hz, Je-= = 3.5 Hz, 2H, Tol), 6.50 (d7 2 ~ p - H = 11 Hz, lH, Hl), 3.43 (d, 4Jp-H = 2.7 Hz, 3H, N-CH,), 2.30 (d,

Je, = 2.2 HZ, 3H, Tol-CH3), 1.01 (s, 9H, C(CH,),). "P-NMR (CD,CN): 6 19.85. 13C-

NMR (CD3CN): 6 178.3 (d, ' J ~ ~ = 7.6 Hz), 140.1 (d, JPC = 13 Hz), 134.2 (d, J,, = 36

Hz), 133.5 (d, J = 78 Hz), 133.1 (d, J = 13 Hi), 130.0 (d, J = 20 HZ), 129.6 (d, J = 10 HZ), 128.9 (d, J = 51 Hz), 127.1 (d, J = 10 HZ), 60.7 (d, 'Je-, = 260 HZ), 37.8 (d, 4Jpc =

5 Hz), 37.3 (d, 'J,, = 26 Hz), 26.5 (s), 20.4 (d, Jp-, = 5 Hz).

Synthesis of Tol(H)PPh,CN(Me)(CO'Bu)*(CO)1C~o(39) Ttimethyl acetyl chloride (98.8 mg, 0.82 mmol), Tol(H)C=NMe (109.2 mg, 0.82

mmol), triphenylphosphine (215.0 mg, 0.82 m o l ) and sodium cobalt tetracarbonyl (160.0 mg, 0.82 mmol) are mixed in 10 ml of CH,CN and the solution is stirred at room

temperature for 30 minutes. The solvent is removed under vacuum and 5 ml of ether is added to the residue. The Light brown powder precipitate is collected by fdtration, washed with ether and dried under vacuum. (308.0 mg, 58% yield). IR (Kbr): 1882, 1596, 1483,

1437, 1097,753, 691, 552 cm? 'H-NMR (CD,CN): 6 7.51-7.74 (m, 15A, PPh,), 7.15

(d, 4 ~ H - H = 8.4 HZ, 2H, TOI), 6.95 (dd, , 4JH-R = 8.4 HZ, , 4Je-n = 2.0 HZ, 2H, TOI), 5.77

(d, 2 ~ p - H = 1 i HZ, lH, (Tol)(P?Ph;)C&), 3.33 (d, 4Jpa = 2.5 Hz, 3H, N-CH3), 2.3 1 (d,

JpmH = 2.2 HZ, 3H, Tol-CH3), 1.01 (s, 9H, C(CH3),). "P-NMR (CH3CN): 6 19.90. "C-

Synthesis of Tol(B)PPh,CN(Me)(CO'Bu)+OTf (40a)

Trimethyl acetyl chloride (10.0 pL, 0.08 mmol), ~ol(H)C=N3de (12.0 pL, 0.08 mmol) and aiphenylphosphine (21.0 mg, 0.08 mmol) are dissolved in 1 ml of CD3CN. Following is the addition of 0.08 mmoles of silver nifiate (21.0 mg) to generate quantitative

yield of 40a. 'Ihe solution is filtered through celie before NMR analysis. 'H-NMR

(CD,CN): 6 7.50-7.75 (m, 15H, PPh, ), 7.13 Id, J = 8.4 HZ, 2H, Tol), 6.94 (dd, J = 8.4

HZ, J,, = 2.0 HZ, 2H, Tol), 5.82 (d, 2T,, = 11 HZ, lH, (Tol)(PPh,')CH-N), 3.3 1 (d, 4Jp- = 2.6 HZ, 3H, N-CH3), 2.31 (d, JM = 2.1 HZ, 3H, Toi-CH,), 1.01 (s, 9H, C(CH3),).

Tol(H)PPh,CN(Me)(CO'Bu)+BAr4- (40b) A simila. procedure to the synthesis of 40a was followed with sodium tetraphenyl

boron instead of silver ainate. 'H-NMR (CD3CN) = 6 7.48-7.78 (m, 15H. PPh,), 7.13 (d,

J = 8-4 HZ, 2H, Toi), 6-94 (dd, J = 8-4 Hz, JP-H = 2.1 HZ, 2H, Toi), 5-77 (d, '~p, = 11

Hz, IH, (Tol)(PPh;)CH-N), 3.30 (d, 4Jp-H = 2.6 Hz, 3H, N-CHJ, 2.30 (d, JP-, = 2.1 HZ, 3H, Tol-CH& 1.00 (s, 9H, C(CH,),).

S yn thesis of Tol(H)(Tol(H)C=NMe)CN(Me)(CO'B u)+Cl- (41) Trimethyl acetyl chlonde (10.0 &, 0.08 m o l ) and Tol(H)C=NMe (30.0 pL, 0.16

mmol) are mixed in 1 ml of CD3CN to fom 41 in approximately 50% yield by 'H-NMR,

in equüibrium with starting materid. (Refer to eq. 2-23 for peak assignment) 'H-NMR

(CD,CN): 6 9-09 6, 1H, H,), 7-26 (d, 2H, Tol,), 7.07 (s, lH, HI), 3.75 (s, 3H, Me2),

3.03 (s, 3H, Me,), 2.39 (s, 3H, Tob-Me), 2.35 (s, 3H, To1,-Me), 1.31 (s, 9H, C(CH,),).

Synthesis of Tol(H)(Tol(H)C=NMe)CN(Me)(CO?Iu)'(CO)Co' (42) NaCo(CO), (15.0 mg, 0.08 mmol) is added to the above solution of 41 to f o m

quantitative yield of 42. The solution is filtered through &te and analyzed by 'H-NMR.

(Refer to eq. 2-23 for peak description) 'H-NMR (CD,CN): 6 8.55 (s, lH, H,), 7.93 (d, J

= 8.4 HZ, 2H7 ToLJ, 7-58 (d, J = 8.4 HZ, 2H9 TolJ, 7-37 (d, J = 7-9 HZ, 2H, Toi,), 7.27

(d, J = 7.9 Hz, 2H, Tol,), 6.99 (s, lH, Hl), 3.71 (s, 3H, Me2), 2.96 (s, 3H, Mel), 2.52

(s, 3H, Tol), 2-40 (s, 3H, Tol,), 1.35 (s, 9H, C(CHJ,.

Synthesis of (CO),Mn[2,5-C,K,(CH=NMe)(Me)J (43a)

Methyl manganese pentacarbonyl (200mg, 0.95 mmol) and Tol(H)C=NMe (127.0

mg, 0.95 mmol) are dissolved in 5 ml of acetonit.de and the solution is heated at 70°C for 24 hours. The solution is concentrated by vacuum mtil fïrst appearance of a soiid, and the

solution is cooled at -30°C overnight. The yellow crystals fonned are collected by filtration,

washed with cold ether and dned under vacuum (190.0mg7 67% yield). IR (Rbr): 2075

(m), 1966 (m), 1910 (s), 1614 (m), 1581 (m), 1431 (w), 1134 (m), 1033 (m), 808 (m),

633 (s), 546 (m) cm-'; 'H-NMR (CD,CN): 6 8.31 (s, lH, H-C=N), 7.72 (s, l m , 7.48 (d,

J = 7.7 HZ, lH), 6.96 (d, J = 7.7 Hz, LH), 3.60 (s, 3H, N-Me), 2.36 (s, 3H, Tol-Me)-

'%-NMR (C,D,, 5°C): 6 220.2, 214.6, 181.5, 176.1, 145.4, 142.1, 141.3, 128.6, 124.8,

51.4, 21.7; Elemental analysis found: C, 52.16%; H, 3.35%; N, 4.63% (caiculated: C, 52.19%; H, 3.37%; N, 4.68%).

Synthesis of (CO),Mn[2,5-C,H,(CH=NBz)(Me)] (43b)

Methyimanganese pentacarbonyl(200.0 mg, 0.95 mmol) and Tol(H)C=NB z (197.0 mg, 0.95 mmol) are dissolved in 5ml of acetonitnle and the solution is heated at 70°C for 72 hours. The solution is concentrated by vacuum and the residual oil is dissolved in 3 ml of

pentane. The solution is placed at -30°C overnight, and large yellow crystals are colleaed by filtration and washed with cold ether (25 1.0 mg, 70% yield). IR (Kbr): 3033 (w), 207 1 (s, sharp), 1994 (vs, broad), 1604 (s), 1580 (s), 1545 (m), 1452 (m), 1345 (m), 1064

(m), 1032 (m), 742 (m), 640 (s), 546 (m); 'H-NMR (CD,CN): 6 8.53 (s, lH, H-C=N),

7.71 (s, lH), 7.58 (d, J = 7.7 Hz, lH), 7.28-7.44 (m, SEC, Ph), 6.99 (d, J = 7.7 Hz, lH),

4.92 (s, 2H, -C&Ph), 2.36 (s, 3H, TolCH3); l3c-~kl~: 6 220.3, 214.2, 182.5, 175.9,

145.2, 142.1, 141.7, 135.8, 129.4, 128.7, 128.5, 124.9, 67.8, 21.8. Elemental analysis found: C, 60.72%; H, 3.48%; N, 3.71% (calculated: C, 60.81%; H, 3.76%; N, 3.73%).

Synthesis of (CO),Mn[2,5-C,H,(CH=NPh)(Me)] (43c) Methylmanganese pentacarbonyl(20.0 mg, 0.95 m o l ) and Tol(H)C=NPh (186.0

mg, 0.95 mmol) are dissolved in 5 ml of acetonitde and the solution is heated at 700C for 5 days. The solvent is removed under vacuum and the residue is recrystallized from a 50/50

mixture of etherlpentane solution at -30°C ovemight The brown/yellow powder is colleciai by filtration, washed with cold ether and dried under vacuun.(l48.0 mg, 43% yield). IR (Kbr): 2077 (s), 1997 (vs), 1944 (vs), 1578 (s), 1538 (m), 1483 (w), 1192 (m), 805 (w),

671 (m), 642 (s), 546 (w); 'H-NMR (CD,CN): 6 8.39 (s, lH, H-C=N), 7.81 (s, lH),

7.65 (d, J = 7.7 Hz, lH), 7.46 (t, J = 8.2 Hz, 2H, Ph), 7.36 (d, J = 8.2 Hz, lH, Ph), 7.28 (d, J = 8.2 Ek, 2H, Ph), 7.03 (d, J = 7.7 Rz, lH), 2.41 (s, 3H, Tol-CH3); 13C-NMR

(c6D6 soc): 6 220.7, 214.5, 213.6, 183.3, 176.2, 153.5, 146.2, 142.5, 142.3, 130.5,

129.1, 126.9, 125.2, 121.8, 21.8;

Synthesis of Tol((CR,),C)C=NH (44)

Ketimine 44 was prepared using a modified fiterature procedd. P-tolunitrile (2.00 g, 17.0 mmol), tert-butylmagnesium chloride (18.7 ml of 1M. Soln. in THF, 18.7 mmol), and 2% (mol equiv.) copper bromide (50.0 mg, 0.35 m o l ) were refluxed in 30.0 ml of TKF under niaogen for 3.5 hours. The solution is allowed to sit at room temperature ovemight The solution is Gitered through celite and tüe solvent is removed under vacuum, leaving 1.3 g of brown oil (44% yield). The product was used without further

puRfication.'H-NMR (CD,CN): 6 7.51 (s, very broad, lH, NH), 7.16 (d, J = 8.4 Hz, 2H,

Tol), 7.12 (d, J = 8.4 Hz, 2H, Tol), 2.33 (s, 3H, Tol-CQ), 1.18 (s, 9H, C(CH,),.

Synthesis of (q '-ToI((CH,),C)C=NH)(C O),,M~(COM~) 45

Methylmanganese pmtacarbonyl (2500 mg, 1.19 mmol) and ketimine 44 (209.0 mg, 1.19 mmol) are dissolved in 10 ml of acetonitrile and the solution is stirred at room

temperature for 15 minutes- Solvent is removed under vacuum and the residual oil is dissolved in 5 ml of pentane, frltered through celite and placed at -30°C overnight. The

yellow crystals fomed are collected by filtration, washed with cold pentane and dried under

vacuum (182.0 mg, 40% yield). IR (Rbr): 3 128 (w, broad), 2971 (w), 2065 (m, sharp),

1954 (vs), 1920 (vs), 1608 (s), 1476 (w), 1388 (m), 1242 (w), 1076 (m), 822 (m), 641

(s), 546 (Ill); 'H-NMR (C6D6): 6 10.76 (s, br, IH, NH), 6.91 (d, J = 7.7 HZ, 2H, Tol),

6.67 (d, J = 7.7 Hz, 2H, Tol), 2.78 (s, 3H. CH,-C(O)), 2.06 (s, 3H, Tol-Me), 0.86 (s,

9H, C(CH3)3); "C-NMR (C6D6 SOC): 6 275.1, 220.1, 213.7, 211.2, 197.9, 188.7, 138.9,

136.4, 129.0, 126.6, 50.1, 43.1, 27.4, 20.9-

Synthesis of (CO),Mn[2,5-C,H,((CH3)3C)C=NPh)(Me)] 46 Methylmanganese pentacarbonyl (180.0 mg, 0.86 mmol) and ketimine 44 (150.9,

0.86 mmol) are dissolved in 10 ml of acetoniscile and the solution is heated at 70T for 20 hours. The solvent is removed under vacuum and the residue is dissolved in 5 mi of ether.

The cloudy solution is frltered through celite and ether is removed under vacuum. The crude product is recrystallized kom 5 mi of pentane at -30T oveniight Light yellow crystals are colleçted by filtration, washeû with cold pentane and dried under vacuum (1 17.0 mg, 34% yield). IR (Kbr): 3372 (s), 2970 (m), 2074 (s, sharp), 1983 (vs, broad), 1898 (s, broad),

1569 (s), 1449 (m), 1360 (m), 1189 (m), 1140 (m), 1041 (w), 962 (m), 852 (m), 646 (s),

544 (m); 'H-NMR (C6D&: 6 8.13 (S. lH), 7.66 (s, br, 1H, MI), 7.57 (d, J = 7.9 HZ,

IH), 6.75 (d, J = 7.9 Hz, 2H), 2.13 (s, 3H, Tol-Me), 0.77 (s, 9H, C(CH3),); 13C-NMR

(c6D6 soc): 6 220.0, 215.7, 214.5, 197.8, 183.0, 142.9, 141.8, 141.0, 130.0, 124.2,

39.6, 27.9, 21.3.

Synthesis of (CO)&n[CH(Tol)N(Me)(COMe)] (51)

Methyl manganese pentacarbonyl (200.0 mg, 1 .O xnmol), Tol@JC=NMe (1 27 -0 mg, 1.0 mmol) and (127.0 mg, 1.0 mmol) are dissolved in 20 ml of acetoniaile and the solution is stirred at room temperature for 24 hours to afford 30% yield @y 'H-NMR)

of complex 51. Attempts to isolate 51 were unsuccessfd. 'H-NMR (CD,CN): 6 7.04 (d =

8.2 Hz, 2H, Tol), 6.89 (d, J = 8.2 Hz, 2H, Tol), 5.09 (s, iH, Mn-Cmo1)-N), 2.98 (s,

3H, N-Me), 2.24 (s, 3H, Tol-CH,), 2.05 (s, 3H, CH,-C(0)-).

Synthesis of (PPh,)(CO),Mn[CH(Tol)N(Me)(COMe)] (52)

Methyl manganese pentacafbOnyl(200.0 mg, 0.95 mmol) , Tol(H)C=NMe (1 27 .O

mg, 0.95 mmol) and alii.minium trichloride (127.0 mg, 0.95 mmol) are dissolved in 20 ml

of acetonitnle and the solution is stirred at room temperature for 24 hours. A 3 ml acetonitrile solution of triphenylphosphine (250.0 mg, 0.95 m o l ) is added with additional stimng for 15 minutes (gas evolution). The solution is concentrated under vacuum until

fht appearance of a solid and solution is placed at -30°C ovemight The pale yeiiow

powder is collected by iïltration, washed thoroughly with cold ether and dried under

vacuum (122.0 mg, 22% yield). IR (KBr): 1996 (s), 1904 (vs, sharp), 1873 (vs, sharp),

1600 (m), 1505 (w), 1434 (w), 1089 (w), 679 (m), 520 (m); 'H-NMR (C,D& 6 7.69 (m,

8H), 6.9-7.5 (m, llH), 4.60 (d. 3~ , , = 19 Hz, lH), 2.22 (s, 3H, N-Me), 1.85 (s, 3H,

Tol-CH,), 1.09 (s, 3H, CH,-C(0)-). 31P-NMR (C,DJ: 6 53.97 (s). Elmental analysis

found: C, 66.33%; ET, 5.14%; N, 2.56%; (Calculated: C, 66.55%; H, 5.06%; N, 2.43%).

Synthesis of (CO),Mn[CH(Tol)N(Bz)(COMe)] (53) Methylmanganese pentacarbonyl (20.0 mg, 0-1 mmol), TolOC=NB z (20.5 mg, 0.1 mmol) and AlQ3 (13.3 mg, 0.1 m o l ) are reacted at room temperature for 24 hours in 1 mi of CD,CN to afford 12% yield (by 'H-NMR) of complex 53. Attempts to isolare 53 were

unsuccessful. 'H-NMR (CD,CN): 6 5.21 (s, lH, Mn-CH(Tol)-N), 5.14 (d, 1 = 16 Hz,

lH, CH,-Ph), 4.32 (d, J = 16 HZ, lH, CH,-Ph), 2.34 (s, 3H, Tol-CH,), 2.23 (s, 3H, CH&(O)-). Aromatic peaks of tolyl group could not be assigned due to the complexity of

the spectra.

Synthesis (CO),Mn[C(O)CH(Tol)N(Me)(COPh)] (54)

Sodium manganese pentaarbonyl (500.0mg, 2.29 m l ) and Tol(H)CN(Me)COPh+Cl- (%a) (630.0 mg, 2.29 mmol) are mixed in 10 ml of açetonitrile

at room temperature for 2 minutes and the cloudy yellow solution is quickly filtered through

celite to remove NaCl. The solution is concentrated by vacuum nntil a yellow solid

precipitate and the cold solution is filtered through a fiitted Buchner funnel. The yellow

powder is collected by filtration, wasbed with cold ether and dried under vacuum (5 12-0

mg, 52% yield). IR W r ) : 2078 (m), 1987 (vs), 1630 (m), 1582 (s, sharp), 1494 (w),

1013 (m), 912(m), 698 (m), 638 (m), 532 (m) cm-'; 'H-NMR (CD,CN): 6 7.57 (m, 5H,

Ph), 7.2 1 (d, J = 8.2 Hz, 2H, Tol), 7 .O7 (d, J = 8.2 Hz, 2H, Tol), 4.54 (s, lH, Me-C(0)-

-(Toi)-N), 3.16 (s, 3H, N-Me), 2.31 (s, 3H, Tol-Me). 13C-NMR (C,D, SOC): 6 269.9,

218-1, 213.1, 212-2, 210.1, 178.0, 137.7, 133.8, 131.2, 130.9, 129.7, 128.7, 127.5,

126.0, 83.0, 41.4, 20.8. Eiemental analysis found: C, 58.07%; H, 3.80%; N, 3-18% (calculated: C, 58.21%; H, 3.72%; N, 3.23%).

Synthesis (CO),Mn[C(O)CH(Tol)N(Bz)(COPh) J (55)

A similar procedure to the synthesis of 54 was followed with

Tol(H)CN(Bz)COPh+Cl- 36b to yield 384.0 mg of 55 (48% yield). 'H-NMR (CD,CN): 6

7.63 (rn, SH), 7.34 (m, 3H), 7-18 (m, 4H), 7.07 (d, J = 8.2 Hz, 2H), 7.05 (d, J = 15 Hz, lH, -C&-Ph), 2.33 (s, 3H, Tol-Me).

Synthesis (CO),Mn[C(O)CH(Tol)N(Ph)(COMe)] (56) A similat procedure to the synthesis of 54 was followed with

Tol(H)CN(l?h)COMe+Cl- 36c to yield 244.1 mg of 56 (48% yield). 'H-NMR (C,DJ: 6

7.25 (d, J = 8.4 Hz, lH), 7.07 (d, J = 7.9 Hz, 2H), 6-93 (m, 6H), 4-72 (s, IH, Mn-C(0)- aUol)-N), 2.06 (s, 3H, Tol-Me), 1.43 (s, 3H, CH,-C(0)-).

Synthesis of (CO),Mn[CH(Tol)N(Me)(COPh) J (60)

Sodium manganese pentacarbonyl (500.0mg, 2.29 m o l ) and Tol(H)CN(Me)COPh+CI' (36a) (400.0 mg, 1.46 mmol) are mixed in 10 ml of acetoniaile and the solution is heated at 5û0C for 15 minutes. Solvent is removed under vacuum and the

residue is dissolved in 10 ml of ether. The red solution is filtered through celite, diluted with 2ûml of pentane and alîowed to sit at room temperature for 16 hours. The yellow solution is collected, leaving a thick red oil precipitate, and the solvent is removed under vacuum. The crude product is extracted with 20 ml of pentane and the extracted solution is placed under reduced pressure to remove the solvent, leaving 252.0 mg of yellow powder

(4396 yield, the product contains trace amount of CO-crystaUized acetonitrile). IR (Kbr): 2014 (s), 1979 (vs), 1951 (vs), 1913 (s), 1589 (w), 1559 (m), 1508 (m), 1474 (w), 1070

(m), 710 (m), 639 (s, broad) cm"; ' H - m m (C6D&: 6 7.09 (m, 2H), 7.01 (m. SH), 6.90

(m, 2H), 5.04 (s, 1H, Mn-CH(To1)-N), 2.49 (s, 3H. N-CH,), 2.16 (s, 3H, Tol-CH,).

13C-NMR (CP, SOC): 6 220.8 (s), 214.8 (s), 212.8 (s), 179.9 (s), 148.8 (s), 133.1 (s),

132.8 (s), 130.6 (s), 129.5 (s), 128.3 (s), 127.6 (s), 67.5 (s), 38.5 (s), 20.8 (s).

Synthesis of (PPh,)(CO ),Mn[CH(Tol)N(Me)(COPh) J (61)

Complex 60 (200.0 mg, 0.5 mmol) and triphenylphosphine (132.0 mg, 0.5 rnmol)

are dissolved in 10 ml of acetonitde and the solution is stirred at OOC for 2 hours (gas

evolution is obsewed). The pale yellow solid is coIIected by filtration and washed with cold ether (140 mg, 52% yield. The product contains trace amounts of acetonitnle). IR (Kbr): 3013 (w), 2002 (s), 1902 (vs), 1868 (vs), 1601 (s), 1504 (m), 1433 (m), 1162 (w), 1089

(m), 1016 (w), 820 (m), 755 (m), 699 (s), 518 (s); 'H-NMR (C6Dd: 6 7.70-7.88 (m, 6H),

7.22 (m, 3H), 6.85-7.08 ( m, lm, 4.59 (d, 'JP-= = 18 Hz, lH, Mn-CH(To1)-N). 2.22 (s,

3H, N-CB,), 2.14 (s, 3H, TOI-CE&). "P-NMR (C6Dd: 6 55.57 (s). 13C-NM~ (C,D, SOC):

8 226.8 (d, 2Jp-c = 84 Hz), 220.6 (d, = 146 Hz), 217.9 (d, 2Jp-, = 84 Hz), 150.0 (d,

Jp-, =30 Hz), 134.2 (d, JP-, = 40 HZ), 133.8 (s), 133.6 (s), 133.1 (s), 132.1 (s), 130.2 (SI, 129-8 (s), 129.1 (s), 128-4 (d, JpC = 35 HZ), 127.6 (s), 74.8 (d, 4 ~ p J P . C = 49 HZ), 38.6 (s), 21.0 (s),

Synthesis of (PPH,)(CO),Mn[C(O)CH(Toi)N(Me)(COPh)] (62)

Sodium manganese pentacarbonyl (300.0 mg, 1.38 m o l ) and Tol(H)CN(Me)COPh+Cl- (%a) (378.0 mg, 1.38 mmoles) are mixed in 10 ml of acetonitrile at room tempera- for 2 minutes and the cloudy yeJlow solution is quickly fîltered through

celite to remove NaCL A 10 ml acetonitde solution of triphenylphosphine (362.0 mg, 1.38 mmol) is added and the resulting solution is stirred at O°C for 2 hours. The pale yeilow solid

is coUected by filtration and washed severaï times with cold ether. (237.0 mg, 37% yield,

the final product contains trace amounts of acetonitrile). IR (Kbr): 2063 (m), 1962 (vs), 1939 (vs), 1624 (s), 1434 (m), 1389 (m), 1328 (w), 1063 (w), 997 (m), 633 (s), 520 (m)

cm-'; 'H-NMR (C,D,): 6 7.76-7.86 (m, 6H), 7.40-7.48 (m, 2H), 7.32 (s, br, lH), 7.26

(d, 2H), 7.02-7.13 (m, 8H), 6.93-7.02 (m, SH), 2.53 (s, 3H, N-CH,), 2.02 (s, 3H, Tol-

Me). "P-NMR (C,D,): 6 52.05 (s). '%-NMR (C,D, SOC): 6 267.6 (d, 'J,, = 50 Hz),

216.9(d, 2Jp-c = 32 HZ), 216.2 (d, 2~p-c = 84 HZ), 214.6 (d, 'JPc = 76 HZ), 213.3 (d, 'JP-,

= 59 Hz), 170-7, 138-0 (d, JK = 54hz)P 135-2, 134.6, 134.0 (d, 'J, = 38 HZ), 132.5,

130.5, 129.9 (d;Jp-, = 27 HZ), 129.7, 128.9, 128.4 (d, = 27 HZ), 83.0 (d, 'J,, = 10 Hz), 36.0, 20.9.

References

(1) Clark, R.J, J.Organomet. Chem 1968, 11, 637.

(2) Hieber, W. Chem. Ber. 1961,94, 1417.

(3) Hermann, B. Synùretic Method of ûrganometallic and Imrgmic Cherrtistry,

Stuttgart, New-york, 1996.

(4) Layer, R.W. Chem. Ber. 1963, 63. 489-510.

(5) Weibeah, J.F.; Hall, S.S. J. Org. Chem. 1987, 52, 390 1-3904.