crown ethers _ applications in inorganic synthesis

8/13/2019 Crown Ethers _ Applications in Inorganic Synthesis

1/44

Colby College

DigitalCommons@Colby

Senior Scholar Papers Student Research

1978

Crown ethers : applications in inorganic synthesisRobert L. Sundberg Colby College

Follow this and additional works at: hp://digitalcommons.colby.edu/seniorscholarsColby College theses are protected by copyright. Tey may be viewed or downloaded from this sitefor the purposes of research and scholarship. Reproduction or distribution for commercial purposesis prohibited without wrien permission of the author.

Tis Senior Scholars Paper is brought to you for free and open access by the Student Research at DigitalCommons@Colby. It has been accepted for

inclusion in Senior Scholar Papers by an authorized administrator of DigitalCommons@Colby. For more information, please contact

[email protected].

Recommended CitationSundberg, Robert L., "Crown ethers : applications in inorganic synthesis" (1978). Senior Scholar Papers. Paper 232.hp://digitalcommons.colby.edu/seniorscholars/232

http://digitalcommons.colby.edu/?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://digitalcommons.colby.edu/seniorscholars?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://digitalcommons.colby.edu/student_research?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://digitalcommons.colby.edu/seniorscholars?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPagesmailto:[email protected]:[email protected]://digitalcommons.colby.edu/seniorscholars?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://digitalcommons.colby.edu/student_research?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://digitalcommons.colby.edu/seniorscholars?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPageshttp://digitalcommons.colby.edu/?utm_source=digitalcommons.colby.edu%2Fseniorscholars%2F232&utm_medium=PDF&utm_campaign=PDFCoverPages


2/44

ROWN ETHERS: APPLICATIONS ININORGANIC SYNTHESIS

byRobert L Sundberg

Submitted in Par t ial Fulfi l lment of the Requirementsfor the Senior Scholars Program

Colby College1978


3/44

APPROVED BY

TUT R

C H A I R M A ~ ? ~ - - - - - ~ ~


4/44

ABSTRACT

The abi l i ty of macroheterocyclic compounds to complex with ionic species hasled to the synthesis and invest igat ion of many multidentate macroheterocyclicspecies . The most s table complexes are formed between macrocyclic polyetheralligands crown ethers) with alkal i or alkal ine earth metal iona. There i s anexcellent correlat ion of the s tab i l i ty of these complexes with the s ize of thecat ion and the s i t e of the cavity in the macrocyclic l igand. Additional factors ,such as the basici ty of the ligand and the solvat ing abi l i ty of the solvent ,also play important roles in the s tab i l iza t ion of the complex.

The s tab i l i ty of such complexes has been advantageously used to increaseanionic react iv i ty and has been successful ly applied to several organic f luorinat ions, oxidat ions, and simi lar react ions. The use of macrocyclic l igands ininorganic syntheses of otherwise di f f icu l t to obtain fluoro compounds has notbeen reported.

O-carborane and m-carborane, C2BlOHl2 are icosahedral cage systems derived2- _from Bl 2H12 by replacement of BH with the i soelectronic CH group. These s tab lemolecules exhibit electron-def icient bonding which can best be explained bydelocal izat ion of electrons. This delocal izat ion gives r i se to s tab i l i ty simi larto that found in aromatic hydrocarbons. Crown ether act ivated potassium f luoridehas been successful ly employed in the conversion of alkyl , acyl and aryl hal idesto their respect ive f luor ides o Analogously hal ide subst i tuted carboranes wereprepared, but their fluoro-derivatives were not obtained.

The appl icat ion of crown ethers in the synthesis of t rans i t ion metal complexesi s relat ively unexplored. The usual synthesis of f luoro-derivat ive t rans i t ionmetal complexes involves highly react ive and toxic f luorinat ing agents such asantimony t r i f luor ide antimony penta f luor ide . bromine t r i f luor ide and hydrogenf luoride, An attempted preparat ion of the hexafluoroosmate IV) ion via a crown


5/44

J/act ivated, or naked f l u o r i e ~ w s unsuccessful. Potassium hexaf l uor oosma t e IV),K20sF6 was eventually prepared using bromine t r i f luor i e as a f luorinat ing andoxidizing agent


6/44

Table of Contents

Introduction

Crown ethers • • • • • • • • • • • • • • • • • • • • • • 2nomenclaturepreparat ioncomplex s tabi l i tyapplications of macrocyclic polyethers

Carboranes • . 0 . • 0 0 6 • • • • • 9 • • • • • • 4 • •bondingchemistry of carboraneshalogen derivativesreact ions of halogen derivat ives

Hexafluoroosmate (IV) ion • • • • • • • • • • • • • • • 15

Experimenta1

materialsspectroscopic measurementspreparat ion of stanting materialsgeneral method used in naked f luoride experimentsattempted preparat ion of F ~ a n d F2C2BlOHICpreparat ion of K20sF6

17

Discussion

Carboranes • • '22

AcknowledgementOsmium compounds • ·27

AppendiX I •Appendix I I 35References • 36


7/44

INTRODUCTION


8/44

Crown Ethers: Applications in InorganicSynthesis

Crown Ethers-Metal complexes of natural ly o c c u r r l n g m g c r n ~ e c y c l ~ such as porphyrin

and corrin r ing derivatives , l have been known for over f i f ty years. During thepast decade a number of synthetic macrocycles capable of binding metal ions havebeen prepared and investigated. The in i t ia l work by Pedersen focused on macrocyclic polyethers or crown ethers . 2,3 Subsequent work by Pedersen4 and others 1• S- 8has led to the synthesis of macrocyclic, macrobicyclic and macrotricyclic moleculescontaining oxygen. nitrogen and sulfur atoms in the r ing.

The most widely studied l igands are macrocyclic polyethers or crown ethers .Pedersen reported that during an attempted synthesis of bis 2- o-hydroxyphenoxy)ethyl) ether from bis 2-chloroethyl) ether and a sodium sa l t of 2- o-hydroxyphenoxy) tecrahydropyran, which contained some catechol. a small amount of a whitefibrous material was formed. 2,3 This white mater ial . dibenzo-l8-crown-6, wasobserved to be quite insoluble in methanol, but readi ly soluble in methanol af te rthe addition of sodium sa l t s 9 This observation led to the discovery of the complexing power of these macrocyclic molecules. There have now been over one hundredroacroheterocyclic molecules prepared and investigated. l• 6,9

NomenclatureThe IUP C nomenclature rules applied to bridged hydrocarbons. such as these

roacrocyclic molecules, give r ise to long and cumbersome names Consequently,Pedersen developed an ad hoc system of nomenclature that i s commonly used. 2 Thename includes a family name. such as crown, and two numbers. the f i r s t of whichrepresents the number of Btoms in the ring and the second the number of functional


9/44

group atoms in the ring. Any addi t ional nonethyleneoxy-substitutions in to ther ing must also be named. For example the name of the compound synthesized byPedersen is dibenzo-lB-crown-6.

Appendix I contains a l i s t of the appropriate names structures and ionsbound by many of the bet te r known synthetic macrocyclic polyethers and polythioetherso However, due to tbe diversi ty of applicat ions of synthetic macrocyclicl igands tbe remainder of this paper shal l be concerned with polyethers commonlyreferred to 8S crowns and a family of bicyclic polyethers cryptands preparedby Leho and coworkers. lO ll

2.2.2.-cryptandPreparation

Appendix II contains a l i s t of review ar t i c l es and other publications dealingwith the preparation of macrocyclic polyethers. The commercial avai labi l i ty ofsome of these compounds has stimulated much of the research in their applicat ions.Because of th is avai labi l i ty the preparations of these compounds will not bediscussed here.

Complex stabi l i tyThe abi l i ty of the crowns and cryptands to complex a metal cat ion appears to

2)


10/44

12be a Lewis acid-base phenomenon. The basic heteroatoms surround tbe cat ion andapparently stabil ize the complex according to the following cr i ter ia

1) size of the ion and macrocyclic cavity;2) number of functional atoms oxygens in crown ethers) ;3) the coplanari ty of oxygen atoms;4) the symmetrical placement of oxygen atoms;5) basic i ty of the oxygen atoms;6) s te r ic hindrances of the polyether ring;7) the tendency of the ion to associate with the solvents;8) electr ical charge of the ion. 1• 2

Perhaps the greatest of these influences are the size of the lon Bnd the sizeof the cavity found in the macrocyclic polyether. Studies have shown that cationstoo large to f i t within the cavi ty are bound less stably than those ions whicheasi ly f i t within the cavity.2,9.13 Depending on the rat io of the diameter of thecavity and the metal ion diameter. 1:1. 1:2. or 2:3 ion: wacrocyclic l igand com-plexes can be formed. 1• 2• l 2,14 However. the fact that a metal ion forms a 1:1complex with a cyclic polyether does not necessari ly indicate that the metal ionis located within the cavity of the macrocyclic compound. For example. the cobal tdichloride dicyclohexano-lB-crown-6 complex can be ei ther a chain or sandwich-typeof complex. 15

Sandwich

lj )


11/44

Chain

The number of functional atoms and the coplanarity of a macrocyclic l igandare important as individual influences upon the complexing abi l i ty of a polyetherbut Pedersen has shown 2 that these two influences are closely re la ted Whenthere are seven or more oxygen atoms present in the polyether ring, the atoms areunable to arrange themselves in a coplanar configuration. 2 Consequently. i f thereare no other at ta inable three dimensional symmetrical configurations. tbe complexwill be less stable than a complex with fewer. but coplanar. functional atoms.

Symmetry is thus an important factor influencing the s tab i l i ty of a poly-etheral or cryptate complex. Where there are more than seven oxygen atoms. ori f the cation to crown ether ra t io s much greater than one. l 6 three dimensionalsymmetry i s often at tainable. The most ommon of these i s a configuration inwhich the oxygen atoms arrange themselves around the surface of a r ight ci rcularcylinder with the apices of the C O C angles pointed toward the center of thecylinder. This configuration i s termed cyl indrical symmetry.2 One of the great-est advantages in using a cryptand 1s the three dimensional symmetry afforded bythem. The cation is completely enclosed within the cryptand leading to such

9)


12/44

very s table complexes as described by Dye and c o ~ o r k e r s 1 7 1 8 Since complexation in croW S and cryptates can be described as a Lewis acid

base phenomenon. the basici ty of the macrocyclic ligand i s fundamental to theformation of a s table complex. The basici ty of the oxygen donors in the r ing canbe affected by inductive effec ts caused by the nonethyleneoxy-substitutions in ther ing. Saturated groups have a greater electron donating abi l i ty than unsaturatedgroups. As a resul t saturated compounds are bet ter coroplexing agents. l 4

Dye19 and Lehn 20 have reported that the activation energy for formation ofthe 2.2.2.-cryptate complex with a sodium cat ion i s higher than for several crownethers . This is to be expected because the additional ster ie hindrance of thecryptands makes complex formation energetical ly l ess favorable. However. the i rstabi l i ty af te r complexation makes their use as a l igand desirable.

The stabi l i ty of a cation complex results from the balance between the freeenergy of the 501ution and of complexation. 21 The solvent plays a major role inthe formation of a complex. Crowns and cryptands can be dissolved in cormoon ,- rorganic solvents and are also soluble in aqueous solutions . Commonly methanol ormethanol-water 2• 9,22 have been used; methanol is a poor solvent for crown ethersbuc an exceltent solvent for the inorganic sal ts 14 Other commonly used solventsare tetrahydrofuran. benzene. diethyl ether and dimethyl sulfoxide.

Applications of macrocyclic polyethersThe abi l i ty of crowns aod cryptands to form complexes with a lka l i and alkal ine

earth metal ions and a l imited number of other ions is the i r moat noteworthycharacterist ic . This property of complexation allows crowns to solubil ize otherwise insoluble ionic compounds in organic solvents.

One of the most in terest ing examples of th is property of crowns was reported

by Ssm and SilJDIlons. 23 They obtained the purple benzene solution of potassiumpermaogaoate by addition of a crown to the benzene. However. th is i s one of the

.6)


13/44

few examples in which an insoluble sa l t can be dissolved in a nonpolar solventl ike benzene simply by adding the crown ether . Normally a more polar solvent,such as methanol, must be used to dissolve the ionic s a l t ~ Z 3 This use of crowns8S complexing agents to increase ionic ac t ivi ty b ~ ~ d application in organicoxidations, where the concentration of the oxidizing agent can be easily controlledwhile in an organic phase, rather than in the more common aqueous phase.

Another practical use that has ar isen for crown ethers i s the i r effect ivenessas agents for the solubil ization of potassium fluoride in polar and nonpolaraprot ic organic solvents. This solubilized fluoride, or naked f luor ide, i s astrong nucleophile, providing a fac i le and eff ic ient means of obtaining organic

24fluoride compounds in high yields . Tradit ional methods for the synthesis offluoride compounds involve more diff icul t and hazardous techniques.

Other anionic species that have been obtained in th is naked form are thehydroxide ion used in saponification reactions,9 superoxide ion obtained frompotassium superoxide in dimethyl sulfoxide. Z5 and cyano groups used to displace

26halogens in organic reactions o Another development has been the use of thechelating effece of the macrocyclic polyethers with potassium hydride in te t ra-hydrofursn to metallate m e t h a n e l ~

Platinum I I ) complexes of te r t ia ry phosphines are usually soluble in organicsolvents but insoluble in water. Alkali sal t s have the reverse solubi l i t ies .

Using a crown ether to solubil ize potassium hydroxide in benzene or dichloromethane. Pt2Cl2(OH)2L2 can be obtained from sym-trans-Pt 2C14LZ where U-PEt3,28P eZPh or PEt2Ph6

Both crowns and cryptands have shown a remarkable abi l i ty to complex a lka l iand alkal ine earth metal cat ions. One development of in te res t i s the dissolutionof potassium and cesium metals in tetrahydrofuran and diethyl ether by perhydrodibenzo-lB-crown-6 forming substantial · concentrations of solvated electrons. 29


14/44

Another report followed with the re la ted dissolut ion of sodium but in this casea crystal l ine sol id could be obtained when 202020-cryptand and a sodium mirror wereput into a cowman solution. The crystals were invest igated and showed what appearedto be a sodium cation contained within the cryptate and another sodium ion outsidethe cryptate with a nearest sodium-sodium distance of 7 006 A that was concludedto be a sodium anion. 17• 18

Crown ethers have been used extensively by Cram and co-workersl2.30-36 incomplexing ammonium ions. The ammonium ions are bound to the oxygen atoms of thernacrocyclic polyether by hydrogen bonds. Another insert ion complex i s formedbetween a crown ether and a diazonium sa l t This complex has also been studiedby Cram and co-workers, but as of yet no crysta l has been obtained0 39

Macrotricyclic molecules can also form stable select ive anion complexes withthe spherical halide anions. Anion complexation was observed by 13C N R spectroscopy. The anion is held ins ide the molecular cavi ty of the cryptand in i t stetraprotonated form by a tetrahedral array of N+-Ht.oX- hydrogen bonds. 37 Thisstructure has been confirmed by the determination of the crysta l s tructure of

4 38[ l ~ c cryptate -H4 ] , where the C indicates that the substrate is includedin the l igand).

8)


15/44

Carboranes

The appl icat ion of crown ethers in organic synthesis i s re la ted to theirabi l i ty to solubi l ize ionic reagents in nonpolar media and thereby increase theact ivi ty of the ionic species. Crown ethers have been employed in the conversionof alkyl , acyl and aryl halides to the i r respective fluorides in ace toni t r i le byl8-crown-6 act ivated potassium fluoride. 24 Analogously, halide-subst i tu ted car-boranes might undergo similar nucleophilic aromatic subst i tu t ion .

1.2-C2Bl I2 and l,7-C2BlOH12, o-carborane and m-carborane respect ively, are2- -icosahedral cage systems derived from B12H12 by replacement of H by the iso-

electronic CH (see Figure I . Carborane chemistry has benefited from intensivetheoretical effor t s directed toward understanding their unique bonding.

BondingCarboranes have electron-def icient s t ructures in which che total number of

4valence electrons i s l ess than the number of atomic orbi ta ls avai lable for bonding.To explain the remarkable s tab i l i ty of such electron-def icient molecules as car-boranes and the heavier boranes, there must be some degree of electron delocal izat ion. This picture of delocal izat ion is also consis tent wich the aromatic character or super aromaticity of c r o r n e s ~ There are two main theoret ical bondingschemes which can effect ively explain such bonding: 1 a local ized three-centerbond approximation. and 2 construction of molecular orbi ta ls extending over the

40entire cage system. Since the former i s more useful in open frameworks whenextensive electron delocal izat ion i s not expected, only the l a t t e r i s applicableto carboranes .

The delocalized bonding and thermal and hydrolytic stabi l i ty of carboranescan also be pictured in terms of resonance stabi l i ty as in aromatic hydrocarbons.

(9)


16/44


17/44

Additional evidence of delocal izat ion of electrons i s found in observed inductive. 41ei f ects in c a ~ e su bs t i t u t i on r e a c t ~ o n S

The high symmetry and evidence of aromatic character make the carboranesreasonable candidates for molecular orbi ta l bonding theor ies. The f i r s t suchcalculat ion was performed by Longuet-Higgins and o b e r t s ~ which led to the pre

2diction of a stable B12Hl2 icosahedral anion. which was la te r confirmed byexperimental resu l ts . These authors assumed that each B-H bond in the moleculeinvolved a normal two-center two-electron bond. leaving three orbi ta ls and twoelectrons on each boron -to be used in the cage framework bonding. Such a systeminvolves 36 molecular orbi ta ls 13 of which are bonding orbi ta ls . The neutral

2molecule has only 24 electrons and consequently the B12H12 ion contains two addit ional ,e lectrons and hence a more stable closed-shel l configurat ion. More complicated and extensive molecular orbi ta l treatments of carboranes have been undertakenby Lipscomb and Hoffrnann. 43,44 Among the most general resu l t s of these LCAO MOcalculat ions are that the carbon atoms are the most posi t ive locat ions on the cage.In ~ r a s t the boron atoms tend to be more negative . the greater the i r distance

45from the carbon atoms. These charge densi t ies are not consis tent with re la t iveelectronegativi t ies of boron and carbon .

Chemistry of carboranesCarboranes exhibi t extraordinary resistance to degradationo Consequently,

i t i s possible to carry out a variety of reactions on subst i tuent groups at tached4 6to the cage, whLle leaving the cage system in tac t . Most of carborane chemistry

involves subst i tu t ions on the carbon atoms ei ther by the react ion of subst i tu tedacteylenes with bis l igand) decaborane compounds such as the synthesis of 1i sopropeny1 carborane from i sopropeny1 ac e ty 1eni!; :

= c -c = H HI . 2H 3


18/44

or by wetal la t ion of the carbons and subsequent react ion with other r g n ~ An example of such a react ion i s the synthesis of o-carboranyl dicarboxylic acid. 41

L i C CLi\ 0lO lO

One of the main motives behind such work is the poss ib i l i ty of incorporat ing thethermally s table carboranes into high polymers such as si l icones to increasethermal s tabi l i ty .47

Halogen derivativesDirect halogenation of carboranes, unlike most react ions carr ied out on these

molecules, leads only to boron-subst i tuted products. Attack by bromine. chlor ineor iodine has been shown to be highly stereospecif ic . Firs t the more negativeboron atoms furthest from the carbon atoms are at tacked, followed by the adjacent

41barons. The carbon atoms and those barons direct ly bonded to them do not appearto undergo electrophil ic Friedel-Crafts halogenation. This observed sequence ofsubst i tu t ion correlates well with ground s ta te charge dis tr ibutions predicted onthe basis of nonempirical molecular orbi ta l methods.45• 48,49 While the s t o i h i o ~

·:letery, cata lys ts and react ion condit ions may affec t the product dis t r ibut ion .the sequence of subst i tu t ion appears invar iant .

Direct f luorinat ion by hydrogen fluoride i s largely non-select ive yie ldingboron-subst i tuted derivat ives containing from one to ten f luorine atoms o Excessf luorine forms B-decafluorocarborane but no subs t i tu t ion occurs at the carbon. 5

Photochemical halogenation by chlorine and bromine i s somewhat less select ivethan Friedel-Crafts halogenation as might be expected for a free radical react ion.The i n i t i a l subst i tu t ion general ly s ta r t s with the boron atoms fur thest frow the

(12)


19/44

carbons, but in the case of chlorine the reaction proceeds unt i l a l l ten borons41have been halogenated. Photochemical bromination proceeds slowly giving only

the mono through tetra-subst i tuted carboranes.

Reactions of halogen derivativesBoron-halogen bonds in carborane derivatives are general ly quite stable . In

contrast to tne hydrolyt ic stabi l i ty of a l l other B-polyhalocarboranes t the B-decafluorQcarboranes will hydrolyze ei ther on immersion in water or exposure to moist

50a ir .n important and dis t inc t ive property of B-halogenated carboranes is the i r

part ic ipat ion in nucleophil ic subst i tut ion react ions with copper I ) chloride.I t has been found that a l l halogen atoms in 9-bromo-. 9-iodo-. 9.l2-dibromo- and9,12-diiodocarboranes are replaced by chlorine when these compounds are treatedwith copper (I) chloride at 250 - 350 0 c. 52 The react ion of 8.9.10.12-tetraiodoo-carborane with excess copper (I) chloride results in the replacement of onlythree iodine atoms by chlorine. 52 The mechanism for these subst i tut ion react ionshas not been established. although Zakharkin and Kalinin53 suggest a four-centert ransi t ion s ta te involving the at tack of copper (I) chloride upon the B-Br bond.followed by the spl i t t ing out of copper I ) bromide.

A related reaction of some synthetic importance is the Ullman react ion ofB-iodo-o-carborane with copper powder in tetrahydrofuran yielding 8.B -bi s (o-carboranyl)0 52

GuTH

Although the boron-halogen bond in carborane halogen derivatives are lessreactive toward nucleophil ic subst i tut ion than the halogen derivatives of benzene

(13)


20/44

and the metallocenes, the appl icat ion of crown ethers in nonaqueous solventsprovides a possible synthetic route to otherwise unobtainable p o l ~ u o r o c r b o r n e s 9-bromo-o-carborane and 9.10-dibromo-m-carborane were obtained by stoichiometricFriedel-Crafts bromination of the respective unsubsti tuted carboranes. Then aser ies of reactions were undertaken va


21/44

Hexafluoroosmate (IV) ion

. The application of crown ethers in the synthesis of t ransi t ion metal complexeshas received l i t t l e at tent ion. But the recent work by Fakley and Pidock 28 indicatesthat t rans i t ion metal alkyl- or aryl-complexes containing cyanide can be obtainedby using crown ethers in organic solvents. The synthesis of f luorinated t rans i t ionmetal complexes usually involves a f luor inat ing agent such as hydrogen f luoride orbromine-trifluoride. Both of these reagents are di f f i cu l t to ~ r with becauseof their high reac t iv i ty and toxic i ty . Consequently, a synthesis of hexafluoroosmate IV) ion via a crown ether act ivated/or naked f l u o r i d ~ ion was undertaken.

In the class ic work of Ruff and his col laborators , although the i r work wasdirected mainly to making simple f luorides such s osmium te t rafluoride and ir idiumtetraf luoride, they observed that f luor inat ion of a metal l ic osmium int imately

, mixed with an alkali-metal f luoride. produced white sa l t l ike subscances6 54These substances were.more careful ly examLned by Hepworth, Robinson and Westland. 54They prepared several quinquevalent sa l ts of osmium and ir idium by fluocinationof the metal or of a metal halide by brominetrifluoride o

The research described within this report was an attempt to prepare potassiumhexafluoroosmate (IV). K20sF6 from osmium tetrabromide, OSBr4654,55 Since l i t t l einformation was found describing the physical charac ter i s t ics of potassium hexa

fluoroosmate (IV), the compound was synthesized by t radi t ional routes employingbromi . f l id . dd.z i d f l S4o m ~ n e t r ~ uor e as an OX1 LZLng an u o r ~ n t ~ n g agent o

The K20sF6 compound obtained i s now being studied by Patterson and co-workersat the University of Maine at Orono to obtain the low temperature luminescence andabsorption spectra. They hope to assign the absorption bands of the electronic

s p e c t ~ y means of a crysta l . f ie ld model with spin-orbit coupling and the vibrational modes using standard group theory methods for octahedral complexes.

15)


22/44

EXPERIMENT L


23/44

MaterialsAnbydrous potassium fluoride Alfa Inorganics) was dried in vacuo for three

hours at 600

C. The anhydrous potassium f luoride was then stored in a deBicatorcontaining r i e r i t e ~ Acetonitr i le Matheson), tetrahydrofuran Baker), a-xyleneMatheson), dimethylformamide Fisher) and dimethyl sulfoxide Fisher) were dis-

t i l l ed and stored over molecular sieves type 5A, Fisher) to insure dryneas.Sulfur dioxide Matheson Gas Products) and r o m i n ~ r i f l u r i d e Matheson Gas Products) were used without further purificat ion.

The crown ether used in a l l reactions was dibenzo-18-crown-6 Aldrich, 98pure). The ether was .dried for two hours at 100 0 and used without further purificat ion. Osmium te t roxide Alfa Inorganics) and hydrogen ~ Q m i d e 4 8 , Matheson)were used as obtained. O-carborane and m-carborane graciously supplied by Professor H. Bushweller of SUNY a t Albany) were used without further purificat ion.

Spectroscopic measurementsAll inirared spectra were obtained using a Perkin-Elmer model 137 spectro

photometer . The samples were in the form of potassium bromide pel le ts . Electronicspectra were recorded on a Perkin-Elmer model 200 UV-VIS spectrophotometer in

11aqueous solution. B N R and GC-MS spectra were obtained a t the University ofMichigan under the guidance of Professor Ro Rudolph.

Preparation of start ing materials9-bromo-o-carborane was prepared by a Friedel-Craf ts bromination of o-carborane

using aluminum tribromide as a catalyst and one equivalent of bromine. This procedure developed y Smith, Knowles and Schroeder56 can be used to obtain al l ofthe mone-, di- , t r i - and tetrabrominated carboranes. In a typical experiment theapparatus used was a SO rol Pyrex glass flask f i t t ed with a ref lux condenser and adropping funnel. 0.027 g of aluminum powder 1.0 mmol) was placed in the f laskand the system was flushed with nitrogen. 0.24g of bromine 1.5 romol was added


24/44

dropwise while cooling the f lask with a water-ice slush. After the formation ofaluminum bromide, 1 .28g of bromine 8.0mmol) w ~ e a d d e d l l5g of o-carborane8.0 mrnol) was dissolved in 10ml of cold carbon disulf ide and th is solution was

slowly added to the chi l led aluminum tribromide-bromine mixture. The mixture waswarmed and then refluxed for two hours. I t went colorless af ter refluxing andthe hot solution was f i l tered The solvent was evaporated, and the products wererecrystallized from hexane. 9-bromo-o-carborane was purif ied by vacuum sublimationa O.953g of product was obtained or a yield of 54 . The melting point was

o 0 56found to be 190-191 C with a reported melting point of 19U C.9,lO-dibromo-m-carborane was prepared in the same manner as described above.

The only change was to double the amount of bromine used in the Friedel-Craf tsreaction. The product was recrystallized from carbon tetrachloride and purif iedby vacuum sublimation. O.61g or a yield of 30 w e r ~ o b t a i n e d af ter sublimation.The melting point was 189 0 C,whicb corresponded to the reported melting point . 56

General method used in naked f luoride experimentsEach reaction was carr ied out in a 50 ml Pyrex glass f lask f i t t ed with a

ref lux condenser. The system was protected from moisture by a Drieri te drying tube.25 mi of dry solvent placed in the reaction f lask along with catalyt ic

amounts of dibenzo-lB-crown-6 and an excess of anhydrous potassium f luor ide.This mixture was s t i r red by a magnetic s t i r r ing device, and af ter 30 minutes thesubstrate waS added•• The mixture was continuously s t i r red and refluxed. Afterrefluxing for 48 hours, a qual i ta t ive tes t for bromide using a chlorine-watermixture was performed. following the l i t e ra tu re procedure 57). When the tes tindicated no bromide present the mixture was refluxed for an addit ional 24 hours.After 72 to 96 hours of refluxing. the mixture was f i l tered while s t i l l warm.Products were Lsolated by recrystall ization and purif ied by vacuum sublimation oraddit ional crystal l izat ions.

18)


25/44

In a typical experiment 0.5 mmo of a bromo-substituted carborane was addedto a solution of 0.145g of n ~ ~ r o u s potassium f luoride (2b5mmolc) and catalyt icamounts of dibenzo-lB-crown-6 ~ 3 6 g , O . l m r o o l . The mixture was refluxed at theboil ing point of the solvent used. Table I summarizes the experiments and the i rresu l t s The reaction products where characterized by melting points and infrared

s ~ e c t r a . which indicated no reaction had occured.

Table ISubstrate Solvent Reflux temperature recovery of substra te

(oC)ace toni t r i le 81 89dimethylformamide _153 9u

d i m e t h ~ sulfoxide 189 04 (decomposed)o-xylene 142 95su I fur dioxide R.T.* 95tetrahydrofuran 66 90

ace toni t r i le 81 90dimethylformamide 153 93sulfur dioxide R.T.* 100tetrahydrofuran 66 82

Since sulfur dioxide i s a gas a t room temperature ~ a l l reactions involving sulfur dioxide were performed in a sealed tubeb

Preparation of K20sF6Osmium tetrabromide was prepared from osmium te t roxide by refluxing with 48

hydrogen bromide following the l i terature procedure (54). The black osmiumtetrabromide crystals were slowly dried over a small flame unti l a l l of the solventwas removed. Then they were dried over a flame for two hours to produce blackfr iable crystals

Osmium tetrabromide i s soluble in d i m e t b ~ sulfoxide, dimethylformamide and

(19)


26/44

acetoni t r i le . Table I I summarizes the reaction conditions that were attempted.In a typical experiment 0.51g of osmium tetrabromide l . O ol) was added to awarm solution of 1.75g of anhydrous potassium f luoride .03 mole) and catalyt icamounts of dibenzo-18-crown-6 .01 mole). The mixture was refluxed for 24 hours,and the hot solution ~ f i l te red. The crystals were isolated by evaporation andrecrystal l izat ion from alcohol-water . The crystals were character ized by electronicspectra and physical appearance.

Potassium hexabromoosmate IV) was prepared following the l i terature procedure55). Similar experiments to those attempted with osmium tetrabromide were under

taken. The products were characterized by electronic spectra . The resu l t s ofthese experiments are also summarized in Table I I .

Table I ISubstrate Solvent recovery of substra te

acetoni t r i le 98dimethyl sulfoxide 97dirnethylformamide 92

ace toni t r i le 100dimethylformamide 97dimethyl sulfoxide 98sul fur dioxide oPotassium hexafluoroosmate IV) was eventually obtained by the oxidation and

fluorination of osmium tetrabromide by bromine t r i f luor ide following the l i t e r a -ture procedure 54). All experiments involving bromine t r i f luor ide were run ina quartz reaction vessel. The yellow compound obtained was character ized byultraviolet-vDDble spectra. A yield of 0.198g of potassium nexafluoroosmate IV)or 27 was obtained from O.493 jo osmium tetroxide.

20)


27/44

DIS USSION


28/44

CarboranesThe infrared spectrum of 9-bromo-o-csrborane Figure II exhibi ts the charac

t e r i s t i c C-H and B-H stre tching regionsa The decrease in the B-H s tretch in tens i tycompared to the same absorption in the spectrum of o-carborane Figure I I I i sdue to the substi tut ion of a bromine atom for a hydrogen atom. The bromine substitut ion has been shown to be select ive subs t i tu t ing f i r s t a t posit ion 9,41 butposit ions 8,9,10, and 12 have nearly equal framework charges.

The infrared spectrum of 9,lO-dibromo-m-carborane Figure IV also exhibi tsthe strong ~ ~ and ~ stre tching absorptionsa Again the B-R absorption of theunsubstituted m-carborane Figure V i s greater than the B-H absorption in the subs t i tu ted species. The subst i tut ion occurs at the 9,10 posi t ions as predicted by

evidence. 4 I ,56,58.59theoretial calculat ions and shown by experimentalProducts from the attempted syntheses of 9-fluoro-o-carborane and 9,10

difluoro-m-carborane were isolated by recrystal izat ion techniques . A qual i tat ive for bromide was performed on the solvents aEter the products were i so la ted .

In i t i a l ly the t es t reagent was s i lver ni t ra te . but the [ Ag dibenzo-18-crown-6)]NO] complex formed making the detection of s i lver bromide di f f i cu l t . A methodemploying chlorine-water was la ter used for the tes t . In a l l cases the t es tindicated that no bromide was present . The infrared spectra and melting points ofthese products also indicated that no react ion had taken place. There was aposs ib i l i ty that small amounts of the desired products were synthesized but theywere int imately mixed with the unreacted substrate. Gas chromatography would bean ideal means to sepQrate the compoundsa A sample which was thought to containsome of the fluoro derivative was sent to the University of Michigan for a GC MSspectrum. Professor Ra Rudolph supervised both GC MS and n· NMR spectra. Bothof these spectra indicated that none of the fluoro der ivat ive was formed.

22)


29/44

-

.- .+' ;C -

1Q lo r J;/]- ...J-Y Lt= .J0C -

r-

- .J}

.J


30/44

-

0tt-. ::L


31/44

r I-

JJ)

fJJIE

J

- jf0n..

c:= == === -


32/44


33/44

The work in this report indicates that the stabi l i ty of the halogen-boron bondi s such that nucleophilic subst i tu t ion i s very di f f i cu l t The hydrolytic stabi l i ty

50of polyfluorocarboranes i s much less than that of the other p o l y h a l o c a r b o r a n ~ Perhaps a greater understanding of nucleophilic subst i tu t ions in carborane moleculecould be obtained by work involving the replacement of f luorine atoms in B-polyfluorocarboranes. The possibi l i ty of employing crown ethers to increase thereactivity of ionic species in the synthesis of B-substi tuted carboranes from B-polyfluorocarboranes remains to be investigated.

Osmium compoundsOsmium tetroxide i s a vola t i le and toxic compound. Therefore great caution

was used in handling and preparing a l l of the osmium compounds.Products from the attempted crown act ivated f luor ide synthesis of potassium

hexafluoroosmate IV) were isola ted by recrystal l izat ion techniques. Potassiumhexafluoroosmate IV) is a yellow solid which dissolves in water producing ayellow solution . All products from the attempted synthesis retained the red osmiumtetrabromide color. botb as a sol id and in solut ion. I f low yields of the productwere obtained the electronic spectra would have indicated the presence of thehexafluoroosroate IV) ion. The electronic spectra however indicated that onlythe bromo derivat ive was present . Other recent s tudies have suggested that whenthe product complex i s anionic/the i so la t ion of the complex is very diff icul t

+because the counter ion [K Crown ether)] s tabi l izes the product in solut ion.There are generally no such diff icul t ies when the role of [K crown ether)] +i s purely catalyt ico I f the hexafluoroosmate IV) ion could be obtained by crownactivated fluoride techniques. i t i s questionable whether the potassium sa l t ofthe complex could be isola ted and purif ied.

In the reaction of potassium bexabromoosmate IV) with cata ly t ic amounts ofdibenzo-18-crown-6 in sulfur dioxide a red solid was obtained. From the infrared

27)


34/44

spectrum of the substance i t was concluded that i t contained no sulfur dioxide.The electronic spectrum of the substance shows the strong absorptions t 490,450 and 250nm ch r cterist ic to the hexabrornoosmate (IV) ion. The substance hadno melting point but decomposed t 235 0 C From the avai lable information t wasconcluded that the red substance i s the [K2 (dibenzo-18-crown-6)] OsBr6 complex.Similar t ransit ion metal complexes have been reported. 28

Crystals of potassium hexafluoroosmate (IV) were obtained following a t r d i -t ional procedure using bromine t r i f luor ide as an oxidizing and fluorinating agent.The crysta ls were characterized by electronic spectroscopy, but no conclusiveevidence was obtained. The cryst l s were given to Dr Patterson and co-workersat the University of Maine. Orono. r Patterson hopes to obtain the low-temperature luminescence and absorption spectra in tbe vis ib le and near infrared regions.Hexafluoroosmate (IV) ions give sharp d-d t r nsi t ion absorptions which do notinvolve the high-intensi ty . short wavelength charge t ransfer bands.

Acknowledgement

The author i s grateful to The Committee to Fund Students Special Projectsfor a grant to subsidize this research, to the Colby College Chemistry Departmentfor their support, and Dr Wayne L. Smith for his helpful discussions and moralsupport.

(28)


35/44

Basic s tructure

12-crown-4

14-crown-4

o15-crown-S

01 0

APPENDIX I

Attached groups

l,2-Benzol,2-Benzo; 5,6-benzo2-Methylj 4-methyl;6-methylj 8-methyl1,2-Cyclohexano

l,2-Benzo; 3,4-benzol,2-Butylbenzoj3,4-butylbenzol,2-Cyclohexanoj3,4-cyclohexanol,2-Butylcyclohexano;3,4-butylcyclohexano

1,2-Benzo

l,2-ButylbenzQI 2-Naph to1,2-Cyclohexyll,2-BuCylcyclohexano1,2-0ecalyl1,2-Benzoj 3,4-benzQl,2-Vinylbenzo (polymer)l,2-Cyclohexanoj3.4-cycLohexanol,2-4-MethylbenzQ

(29)

Ions bound by l igands

N8,K

L i Na. K, Rb

Li. NaLi,Na,lC,Rb

Na,K

Li,Na,K

Li,Na.K

Li,Na,K,Cs

K

Li.Na,K,Rb,Cs

Na,K


36/44


37/44

I

18-crown-6 (continued)

I9-crown-6

b20-crown-7

~ ~ ( 3lj

21-crown-7

c1VJ ?l f

24-crown-8

1,2-Benzo; 3.4-benzo;7,8-benzol,2-2,3-Napbtho1,2-2.3-Naphtho;5.6-2.3-naphtho1,2-Vinylbenzo (polymer)

1.2-Benzo; 3.4-benzol,2-Benzo; 3.4-benzo5.6-benzQ

1.2-Benzo;J,4-benzo1.2-Benzo; 3.4-benzo;5-pentamethylene

1.2-Benzo; 3,4-benzo;5-oxygen

1.2-Benzoj 3,4-benzoa1.2-Cyclohexano; 3,4cyclohexano1.2-Benzo; 3,4-benzo;S,6-benzo

a1,2-Benzo; 5,6-benzol,2-Cyclohexano; 5,6cyclobexaoo

1 2 B ~ n £ o ~ ~ 3 ; Q ~ ~ e t i ? o t 5.6-benzo; 7,8-benzo1.2-2,3-Naphthoj 5,62,3-naphtho

Li.Na,K,Rb

Li,Na,K,Rb,Cs

K

K Cs

K.Cs.Na,LiK CsLi,Na,K,Cs.Rb

K Cs

Li,Na,K,Rb,Cs


38/44

30-crown-10

60-crown-20

1 1 1 - c ryp t and

1.1.2. -cryptane

2.10 2. -crypta nd

2.2.2. -cryptand

l 2-Cyclobexano; 3 4cyclohexano

1 2-Benzo; 3 4-benzo1 Z-Cyclohexano; 3 4cyclohexano

. 1 : d. : ) .. - ; 0 ; :

•• J

1 2-Benzol l-Benzo; 3-4-benzQ

32)

Li Na K Rb

K

H,Li

Li,Na,K,Rb,Cs,MgCa Ba. Sr

Li,, Na.K, Rb,Cs. gCa Sr Ba

Li Na K Rb Cs MgCa Sr Ba Tl +Na,K,BaNa,K,Ba


39/44

3.2.2.-cryptand

3.2.3.-cryptand

3.3.3.-cryptand

1.4-dithia-1S-crown-5o A S1,4-dithia-18-crown-6

1.7-ditbia-1B-crown-6

2,3-4-Metbylbenzo

2.J-4-Methylbenzo

8.9-Benzo; 17,18benzo

Li,Na.K,Rb,Cs.MgCa. Sr. Ba

Li.Na.K,Rb,Cs.M.gCa,Sr,Ba

Li.Na,K,Rb,Cs,MgCa.Sr.Ba

K Ag

K Ag

K.Ag

33)


40/44

l,10-dithia-18-crown-6

14,l5-Benzo K)Ag

8,9-Benzo;benzo 17,18 K,Ag

S l tl 4 10 l3- te t ra th ia18-crown-6

2,3-Methylbenzo; Na.K,Ag11.12-methylbenzo

II a Na,K,Ag\:1

a These macrocyclic l igands are able to complex ions without addi t ional nonechyleneoxy substi tut ions .For a more complete compilation of ion binding synthetic mult identateroacrocyclic ligands see J . J . Christensen. D. J . Eatough and R.M. Izat t Chern.Rev•• 351 1974).

34)


41/44

APPENDIX IIPublications dealing with synthetic procedures for the preparation of

rnacrocyc1ic ligands.Macrocyclic polyethers

L C.J. Pedersen. J . Am. Chern. oc 89. 7017 (1967)2. C.J. Pedersen, J Am. Chern. Soc •• 92. 386 391 (1970)3. C.J. Pedersen. J . Am. Chem. Soc •• 89, ~ S (1967)4, C.J. Pedersen and H.K. Frensdorff. Angew. Chern. Internat .

Edit •• 11. 16 (1972)5. G.W. Gokel and H.D. Durst. Syntheses. 516 (1976)6. Newkone. McClure, Simpson. and Danesh Khoshboo. J Am.Chern. Soc •• !ll.. 3232 (1975)7. Tarnowski and Cram. J. Chern. Soc. Chern. Comm •• 661 (1976)8. Parsen. J Chern. Soc•• Perkin, 245 (1975)9. Krespan. J Org. Chern •• 12. 3144 (1974)

For practical purifications of l8-crown-6 see:1. Goke1, Cram, Liotta. Harris, and Cook. J Org. Chern ••

~ 2445 (1974)2. Tina-Pol and Grunwald, J. Am. Chern. Soc •• ~ 2879 (1974)

Macrocyc1ic po1ythioechers1. Oc ymowyc z , Mak. and Michna. J Org. Chem. ) 2079 (1974)2. W. Rosen and D. H. Busch. J Ain. Cbem. Soc •• 4694 (1969)2. ..3. W Rosen and D.H. Busch. J Chern. Soc. Chern. Comma • 148 (1969)4. w Rosen and D.H. Busch. Inorg. Chem •• 2., 262 (1970)

Macrocyc1ic polyam ines1. A,B.P. Lever. Advan. Inorg . Chern. Radiochem .• I. 27, (1965)2. J J Christensen. D.J. Eatough and R.M. Izat t Chern Rev., 74.

351 (1974) and references therein.

35)


42/44

REFERENCES

1 J . J . Christensen, D. J . Eatough and R. M. Izat t , Chern. Rev. , 74, 351 (1974) •2) C. J. Pedersen, J . Am. Chem. Soc. , 89, 7017 (1967) •3) C. J . Pedersen, J . Am. Chern. Soc. , 89, 2495 (1967).4) C. J . e e r s e n ~ J. Org. Chern. 36, 254 (1971).5) A. B. P. Lever Advan. Inorg. Chern. Radiochem. , 2. 27. (1965) •6) G. W Goke1 and H. D. Dur s t Synthesis, 516 (1976)7) J . Smid. Appl. Chern. , 48)' 343 (1976) and sources therein.8) M. Newcomb, G. W. Goke1 and D. J . Cram. J . Am. Chern. Soc. J 96 6810 (1974),9) c. J . Pedersen and H. K. Frensdorff, Angew. Chern, 84, 16 (1972).

10) B. Dietrich. J . M. Lehn. and J . P. Savrage. Tetrahedron Lett . 1969. 2889.11) J . M. Lehn, Accounts of Chemical Research. 1 ~ 49 (1978).12) R. M. Izat t . D. P. Nelson. J . H. R y t t i n g ~ B. L. Haymore and J . J . Christensen,J. Am. Chern. Soc •• 93. 1619 (1971).13) K. H. Wong. G. Konizer and J. Smid, J . Am. Chern. Soc •• 21. 666 (1970).14) C. J . Pedersen, J . Am. Chern. Soc., 92 386 & 391 (1970).-15) A. C. L. Su and J . F. Weiher, rnorg. Chern., 2, 176 (1968).16) D. N. Reinhoudt, R. T. Gray, F. Dejong and C. J . S m i t ~ Tetrahedron. 33, 563(1977).17) J . L. Dye. J . M. Ceraso. M. T. Lok, et a l •• J . Am. Chern. Soc., 2&, 608 (1974).18) F. J . Tehan, B. L. Barnett, J . L. Dye, J . Am. Chem. Soc •• 7203 (1974).19) J . M. Ceraso, J . L. D y e ~ J . Am. Chern. S o c ~ 4432 (1973).20) J . M. Lebn, J .P . Sauvage. B. Dietrich, J . Am. Chern. Soc., 21, 2916 (1970).21) J . M. Lebn, and J . P. S a u ~ a g e J J . Am. Chern. Soc •• 12. 6700 (1975)22) H. K. Frensdorff. J . Am. Chern. Soc •• 2 1 ~ 600 (1971).23) D. J. Sam and H. E. Simmons, J . Am. Chem. Soc., 94.4024 (1972).24) C. L. Lio t ta and H. P. Harris, J • .Am. Chern. Soc. J 94, 2250 (1974).

6 )


43/44

25) J . S. Valentine and A. B. Curtis , J . Am. Chern. Soc. , 21., 224 (1975) .26) T. Sasaki, S. Eguchi, M. Ohnoond, F. Nakata, J . Org. Chem 41, 2408 (1976) •27) E. Bunce1 and B.. C. Menon, J . Chern. Soc •• Chern. Comm., 64 (8) (1976).28) M. E. Fakley and A. Pidcock, J . Chern. Soc. Dalton, 1444 (1977) .29) J. L. Dye, M G. DeBacker and V. A. Nicely. J . Am. Chern. Soc., zz 5226 (1970) •30) W. D. Curtis , R. M. King, J. F. Stoddart and G. H. Jones, J . Chern. Soc. Chern.Comm•• 284 (1976).

31) J. M. Timko, et aI J. Am. Chern. Soc •• ~ 7097 (1974).32) R. C. Helgeson, J . M. Timko and D. J . Cram. J . Am. Chern. Soc., 22, 7380 (1974).33) E. P. Kyba et aI J. Am. Chern. Soc., 12, 2692 (1972).34) R. C. Helgeson, K. Koga, J . M. Timko and D. J . Cram, J . Am. Chern. Soc., ~3021 (1974).35) R. C. Helgeson et aI, J . Am. Chern. Soc., 22 6762 (1974).36) L. R. Sousa, K. H. Hoffman, L. Dap1an and D. J . Cram, J . Am. Chern. Soc., 2E,7100 (1974).37) E. Graf and J . M. Lehn, J . Am. Chern. Soc., 98 (20), 6403 (1976).38) B. Metz, J . M. Rosa1ky and R. Weiss, J . Chern. Soc., Chern. Comm. 533 (l976).39) K. Madan, D. J . Cram, J . Chern. Soc•• Chern. Comm., 481 (1973).40) R. N. Grimes, Carboranee , 1st ed , , Academic Press, Lnc , , New York, N.Y.,1970, p 13.41) ibid, chapters 6 and 7 and references therein.42) ibid, p. 17.43) R. Hoffmann and W. N. Lipscomb, J . Chern. Phys., ]&, 2179 (1962).44) R. Hoffmann and W. N. Lipscomb, J . Chern. Phys.,37, 2872 (1962).45) R. Hoffmann and W N. Lipscomb, J. Chern. Phys., 36, 3439 (l962)46) R. N. Grimes, Carboranes . 1st ed., Academic Press, Inc. , New York, N.Y.•

1970, p 65.47) F o A. Cotton and G. Wilkinson, Basic Inorganic Chemistry , 1st ed. , JohnWiley and Sons, Inc.) New York. N.Y. 1976, p. 241.48) J . A Potenza and W. N. Lipscomb; Inorg. C h e m ~ 1471 (1966).

37)


44/44

49) J Ao Potenza, W No Lipscomb. Go D. Vickers and H. A. Schroeder, J AmChern Soc •• 88. 628 (1966).

50) S. Kongpricha and H. A. Schroeder, Inorg. C h e m ~ 2449 (1969).51) H. Schroeder, T. L. Heying, J R. Reiner. lnorg. Chern., 1 1092 (1963).52) R. N. Grimes, Carboranes , 1st ed Academic Press, Inc •• New York, N. Y.,1970, p. 143 and references therein.53) L. I Zakharkin and V. N. Ka1inin., Izv. Akad. Nauk SSSR, Sera Khim. p. 25771967) •54) M A. Hepworth, P. L. Robinson and G. J Westland. J Chem. Soc •• 4269 (1954).55) F. P. Dwyer and J W Hogarth. Inorg. Synth.,2, 204 (1957).56) H. D. Smith, T. A. Kuowles and H. Schroeder, Inorg. Chern., ~ 107 (1965).57) W. B. Meldrum, E. W. Flosdorf and A. F. Daggett, Semimicro Qualitative Analysiof I n o r ~ a n i c Materials. , 1st ed •• American Book Company, New York. N.Y. 1939, p. 258) H. A. Beall, and W N. Lipscomb, Inorg. Chem',2J874 (1967).59) c. O. Oben1and and S. Papetti , J Org. Chem. 31 3868 (1966).J I

crown ethers _ applications in inorganic synthesis

Documents