6. ORGANOMETALLIC COMPOUNDS By Alwyn G. Davies (Department of Chemistry University College Cower St. London. W.C.1) ACTIVITY in the field of organometallic chemistry continues to increase and it is illuminating to compare the number of references which the Annual Surveys of Organometallic Chemistry have given to the compounds of the non- transition metals in the past three years 1964,900;’“ 1965 1200;Ib 1966,1800.“ A comprehensive account of work yblished during 1967 will be available in the Annual Survey (1968);’“ this present report therefore does not attempt to cover the whole field but rather tries to point out the principsl current trends. Only review articles are listed fairly comprehensively. Three monographs on general organometallic chemistry have been published during the year two will be useful principally as textbooks in undergraduate courses.2*3 The third,4 being the first of two volumes of the third edition of G.E. Coates’s ‘Organometallic Compounds’ will be invaluable also as a reference work for specialists in the field. It deals with the organic compounds of all the non-transition metals except silicon phosphorus and arsenic. It includes many references to work published in 1967 and is the best single source of the background information to this Report. The second volume,’ covering the transition metals will be published early in 1968. The abstracts of the lectures which were presented at the Third International Symposium on Organometallic Chemistry which was held at Munich in August and September show the breadth of current work ;the plenary lectures are to be published in a volume of Pure and Applied Chemistry.General reviews published during the year include the following the mech- anisms of electrophilic substitution of metal alkyls,6 the influence of co-ordina- tion on the reactivity of organometallic compounds,’ insertion reactions of compounds of metals and metalloids involving unsaturated substrates,’ transition metal intermediates in organic synthesis,’ and organometallic pseudohalides. lo Ann. Surveys Organometallic Chem. (a) 1965 1; (b) 1966 2; (c) 1967 3; (d) 1968,4. P. L. Pauson ‘Organometallic Chemistry,’ Arnold London 1967. J. J. Eisch ‘The Chemistry of Organometallic Compounds. The Main Group Elements,’ Macmillan London 1967.G. E. Coates M. L. H. Green and K. Wade ‘Organometallic Compounds,’ vol. 1; G. E. Coates and K. Wade ‘The Main Group Elements,’ Methuen London 1967. ’ Ref. 4 vol. 2 M. L. H. Green ‘The Transition Elements,’ Methuen London 1968. ‘M. H. Abraham and J. A. Hill J. Organometallic Chem. 1967,7 11. ’ 0.Yu. Okhlobystin Russ. Chem. Rev. 1967,36 17. M. F. Lappert and B. Prokai Adv. Organometallic Chem. 1967,5 169. C. W. Bird ‘Transition Metal Intermediates in Organic Synthesis,’ Logos Press London 1967. lo J. S. Thayer and R.West Ado. Organometallic Chem. 1961,5 169. H Alwyn G.Davies Analytical Methods.-When organic derivatives of metals such as lithium magnesium or boron are used in synthesis they are usually prepared then caused to react in situ without being isolated.It is important then that simple and accurate methods should be available for detecting and analysing these compounds in solution. Reagents which will add to a carbonyl group (e.g. RLi RMgX R,Zn) are usually detected by Gilman’s ‘Colour Test 1’’ in which they are treated with Michler’s ketone to give a tertiary alcohol (1) which liberates a blue or green carbonium ion when acid is added. RM + (p-Me,N*C,H,),CO + R(p-Me,N-C,H,),C*OH (l) R(kMe2N*C6H4)2C+ Acetic acid is usually used when both alkyl- and aryl-metallic compounds respond to the test. If the weaker acid catechol is used only the triaryl- methanols (1;R = aryl) ionise enabling the alkyl- and aryl-metallic compounds to be distinguished.Alternatively the coloured solution resulting from the usual test can be treated with aqueous sodium hydrogen sulphate when the colour will be discharged only if R is alkyl.’ ’ Organolithium compounds are usually estimated by a double-titration method. The total of RLi and the ROLi which is usually present as an impurity is determined by titration with acid. The RLi is then caused to react with benzyl chloride or 1,2-dibromoethane the residual ROLi is titrated and the initial concentration of RLi is obtained by difference. Some lithium alkoxides however react slowly with the organic halides which scavenge the alkyl- lithium reducing the accuracy of the method. It is better then to titrate a known amount of benzoic acid in a dimethyl sulphoxide4imethoxyethane-hydrocarbon solvent using triphenylmethane as the indicator.” The reactions involved are RLi + PhC0,H -+ PhC0,Li + RH -+ RLi + Ph,CH -+ RH + Ph3CLi (red) Grignard reagents containing other magnesium bases can be determined by a double-titration procedure in which carbon tetrachloride is used as the organometallic scavenger.’ Alternatively an alkyl-lithium or alkyl-magnesium halide may be titrated with butanol in an ether or .hydrocarbon containing a trace of 1,lO-phenan-throline or 2,2’-biquinolyl.The amines form highly coloured charge-transfer complexes with the organometallic compounds and the colours are discharged sharply at the equivalence point. Metal alkoxides do not interfere. l4 Organoboranes are usually analysed by estimating the boric acid which is l1 J.M. Gaidis J. Organometallic Chem. 1967,8 385. l2 R. L. Eppley and J. A. Dixon J. Organometallic Chem. 1967,8 176. l3 T. Vlismas and R. D. Parker J. Organometallic Chem. 1967,10 193. l4 S. C. Watson and J. F. Eastham J. Organometallic Chem. 1967,9 165. Organometallic Compoundr 221 formed when the boron-carbon bonds are cleaved by alkaline hydrogen per- oxide. It has now been shown that trimethylamine oxide quantitatively oxidises a wide range of organoboranes to alkoxyboranes and titration of the trimethylamine which is evolved gives a method of estimating the R-B groups. It seems unfortunately that the method cannot readily be extended to include derivatives of aluminium or magnesium.' R-B< + Me,NO -+ROB<+ Me,N Group 1.-The organolithium compounds have recently been recognised to belong to the class of alkyl-bridged electron-deficient oligomers which includes also the corresponding compounds of beryllium magnesium and aluminium.Crystalline methyl-lithium contains tetrahedra of lithium atoms with a methyl group centred above each face. Hexamers may occur in solution or in the gas phase ;these probably consist of chair-shaped hexagons of lithium atoms with an alkyl group located above the exo-face of the plane formed by any three adjacent atoms.' Colligative measurements show that organolithiums in ether or tetrahydro- furan may or may not remain associated depending on the structure of the organic groups. Methyl-lithium remains predominantly a tetramer phenyl- lithium is a dimer and benzyl-lithium is a monomer ;in these last two compounds the co-ordination shell of the lithium contains also solvent molecule^.'^ The interaction of these species with other organometallic compounds in solution can be followed by 'H and 7Li n.m.r.spectra. Ethyl-lithium in benzene slowly exchanges its ethyl groups with diethylmercury ;with diethylcadium in benzene the reaction is fast but the intermediate complex LiCdEt, through which exchange occurs can be detected only in ether solution. Diethylzinc on the other hand forms the complex LiZnEt in both solvents.'8 In ethers phenyl-lithium reacts with other organometallic compounds to give the species (Li,MePh), Li,Me,Ph Li,MgMe,-,Ph, Li,MPh, and LiMPh (M = Zn or Mg)." One of the important uses of butyl-lithium is for lithiating organic compounds by the reaction Li-G Ha -+ LiR + BuH The nucleophilic power of the butyl group is increased by additives or solvents which co-ordinate to the lithi~m,~ and in the presence of potassium t-butoxide butyl-lithium will lithiate even benzene and add to ethylene at room tempera- ture.,' Butyl-lithium lithiates dimethyl sulphide in the presence of NNN'N'-tetramethylethylenediamine giving CH S *CH2Li,21 and the corresponding R.Koster and Y. Morita Annalen 1967,704 70. T. L. Brown Adv. Organometallic Chem. 1965,3 365. " P. West and R. Waack J. Amer. Chem. SOC. 1967,89,4395. '* S. Topper G. Slinex and G. Smets J. Organometallic Chem. 1967,9,205. l9 L. M. Seitz and T.L. Brown J. Amer. Chem. SOC. 1967,89 1602 1607. 2o M. Schlosser J. Organometallic Chem. 1967,8,9. D. J. Peterson J. Org.Chem. 1967,32 1717. Alwyn G.Davies oxygen compound CH3 0 CH2Li has been prepared from the reaction between chloromethyl methyl ether and metallic lithium.22 Both reagents show the usual substitution and addition reactions of organolithium compounds and are useful in preparing further methoxymethyl- and methylthiomethyl- compounds. The thioacetals are lithiated more readily than the thioethers and provide a route to ketones by the reaction :23 The extension of this to the preparation of silyl and germyl ketones (R and/or R! = R"',Ge or R"',Si) is described in a later section. The orthothioformates react with butyl-lithium in tetrahydrofuran at -78",and the products (RS),CLi are again useful intermediates in synthesis.24 Tri(pheny1thio)methyl-lithiumis interesting as it appears to present an example of a carbenoid molecule (2) in equilibrium with its carbene (3) It slowly decomposes to tetra(pheny1thio)ethylene (4) and the rate decreases if phenylthiolithium is added.Tri(pheny1thio)methyl-lithium reacts with p-tolythiolithium and tri(p-to1ythio)methyl-lithium with phenylthiolithium to give the same mixture of compounds (PhS),(C7H,S)3-nCLi (n = 0-3) and the same four compounds are formed in the ratio of approximately 1 :2:2 1 when (PhS)3CLi and (C,H,S),CLi are mixed. Electrophiles such as cyclo- hexene epoxide which cannot attack the bulky carbenoid trap the phenyl- thiolithium and drive the equilibrium to the right increasing the yield of olefin.Certain nucleophiles on the other hand will trap the carbene :tributylphosphine reacts in 5 hr. at room temperature to give the ylid (5) in 80% yield and 1,l-dimethoxyethylene and 1,l -di(phenylthio)ethylene give the corresponding cyclopropane derivative^.^' The chemistry of stable a-halogenoalkyl-lithium compounds and the mech- anisms of their carbenoid reactions have been reviewed.26 Details have been published for preparing pure phenyl- p-tolyl- p-anisyl- and p-chlorophenyl-lithium from butyl-lithium and the appropriate aryl iodide 22 U. Schtillkopf H. Kupers H.-J. Traencker and W. Pitteroff Annalen 1967,704 120. 23 E.J. Corey and D. Seebach Angew. Chem.Internat. Edn. 1965,4,1075,1077. 24 D.Seebach Angew. Chem. Internat. Edn. 1967,6,442. " D.Seebach Angew. Chem. Internat. Edn. 1967,6,443. z6 G. Kobrich Angew. Chem. Internat. Edn. 1967,6,41. Organometallic Compounds 223 crystalline phenyl-lithium for example is obtained with a purity of about 99-8%.27 Phenyl-lithium reacts with 1-chlorocyclo-pentene -hexene and -heptene to give the corresponding 1-phenylcycloalkenes. The rates and products when the alkene ring is labelled with deuterium establish that the reaction proceeds predominantly if not exclusively through an elimination-addition reaction involving the cycloalkyne intermediate.2* Group 11.-A distinction can be drawn in Group 11 between the organic compounds of beryllium magnesium zinc and cadmium and those of mercury.The first group of compounds have a very reactive carbon-metal bond (e.g. towards oxygen or water) and interest is still centered on the structures of these compounds and the equilibria they undergo. The organomercury com- pounds have a much less reactive carbon-metal bond; their constitutions are relatively simple and interest centres on the way this bond may be formed or broken and on the potential these reactions have in organic synthesis. Relatively little is known about organoberyllium chemistry. The preparation and structure of many of its simple compounds have been reported largely by G. E. Coates and his a~sociates,~’ who have also reviewed the field.30 For the past two or three years there has been general agreement that the constitution of a Grignard reagent in an ethereal solvent can be represented by the following series of mobile equilibria in which the magnesium has its co-ordination number raised to at least 4 by co-ordination of solvent.The monomeric species RMgX is the principal entity present but binuclear species may be important in concentrated solutions and in less polar solvents. The current picture has been reviewed.* 31 Recent work on the thermochemistry of the reactions between diethyl- 27 M. Schlosser and V. Ladenberger J. Organometallic Chem. 1967,8 193. ’* L. K. Montgomery and L. E. Applegate J. Amer. Chem. SOC. 1967 89 2952; L. K. Mont-gomery A. 0.Clouse A. M. Crelier and L. E. Applegate Ibid. p. 3453. 29 G. E. Coates and M.Tranah J. Chem. SOC.(A) 1967 236 615; G. E. Coates and A. H. Fish-wick ibid. p. 1199. 30 G. E. Coates Record Chem. Progr. 1967,28 3; ref. 4 pp. 103-121. 31 E. C. Ashby Quart. Rev. 1967,21,259. ” A. G. Davies and P. G. Harrison J. Chem. So?. (C),1967,298. Equilibria of this type must be expected whenever a metal which is formally not co-ordinatively saturated carries two mobile ligands at least one of which is capable of bridging. Dibutyltin chloride methoxide Bu,Sn(OMe)Cl for example has been suggested to behave in this way.” 224 Alwyn G. Davies magnesium or diphenylmagnesium with magnesium chloride or magnesium bromide,33 and on the fluorine n.m.r. spectra of p-fluorophenylmagnesium compounds has supported this.34 The halogen bridges in MgCl and MgBr in ether are much stronger than the alkyl bridges in Me,Mg and Et,Mg substan- tiating the assumption that association of the Grignard reagent occurs through the halogen rather than the alkyl groups.35 Similarly in the crystal the amine complex (EtMgBr,NEt,) is bromine-bridged with 4-co-ordinate magnesium and a trans-disposition of the remaining four ligand~.,~ There was previously some doubt whether dialkylberylliums and beryllium halides could take part in equilibria with the alkylberyllium halides.Studies of the ebullioscopy the n.m.r. spectra and the reaction with dioxan of a mixture of dimethylberyllium and beryllium bromide shows that such equilibria do indeed obtain. A 2 1 mixture of Me,Be and BeBr in ether at -75” shows two n.m.r.signals one for Me,Be and one for MeBeBr but at 35” these signals coalesce because of the rapid intermolecular exchange of methyls.37 Diethylzinc and zinc iodide or bromide react slowly in ether at room tempera- ture to give the monomeric species EtZnI and EtZnBr which can be isolated as their complexes with NNN‘N’-tetramethylethylenediamine ; the species Et,Zn and EtZnX however cannot be distinguished by ‘H n.m.r.38 In hydro- carbon solvents. on the other hand the chemical shifts are significantly different but in mixtures of Et,Zn and EtZnX (X = C1 Br I) the signals of only one type ofgroup are apparent interpolated iu position between those of the components implying that rapid exchange occurs even at -60°.39 In the crystal unsolvated ethylzinc iodide is co-ordinatively polymerised by bridging iodine ;40 in contrast the corresponding magnesium compounds consist of mixtures of the species (R,Mg) and MgX2.41 The ethylation of phenylmercuric chloride by diethylzinc is kinetically first- order in each reagent and the relative reactivity of various dialkylzincs (Me < Et < Pr < ‘Pr) has been interpreted as implying an S,i mechanism for the reaction.42 The acidolysis of dipropylzinc by p-toluidine or cyclohexyl- amine in di-isopropyl ether appears to follow a similar mechanism.43 Organozinc urea derivatives (e.g.EtZn -NPh CO NPh,) are trimeric in solution and its has been suggested that they bring about the trimerisation of co-ordinating isocyanate molecules by a ‘template’ mechanism,44 rather 33 M.B. Smith and W. E. Becker Tetrahedron 1967,23,4215. 34 D.F.Evans and M. S. Khan J. Chem. SOC.(A) 1967,1643,1648. ” E. C.Ashby and F. Walker J. Organometallic Chem. 1967,7 P17. 36 J. Toney and G. D. Stucky Chem. Comm. 1967,1168. ’’ E.C.Ashby R. Sanders and-J. Carter Chem. Comm. 1967,997. ” M. H.Abraham and P.H. Rolfe J. Organometallic Chem. 1967 7 35. 39 J. Boersma and J. G. Noltes J. Organometallic Chem. 1967,8 551. *O P.T. Moseley and H. M. M. Shearer Chem. Comm. 1966,876. 41 E. Weiss Chem. Ber. 1965,98,2805; Ann. Reports 1965,62 281. 42 M. H. Abraham and P. H. Rolfe J. Organometallic Chem. 1967,8 395. 43 M. H. Abraham and J. A. Hill J. Organometallic Chem. 1967,7 23. 44 J. G.Noltes and J. Boersma J. Organometallic Chem. 1967,7 P6.Organometallic Compoundr 225 than the repeating ‘insertion’ process which was proposed for the reaction in- volving alk~xides,~~ Improvements have been reported in the preparation of dimethylzinc and diethylzinc from the alkyl iodides and zinc and the stability of the com- plexes formed between various dialkylzincs and 2,2’-bipyridyl or tetramethyl- ethylenediamine have been inve~tiaged.~~ Mercury. Organomercury compounds are prone to react by both electro- philic attack on the carbon and by a homolytic mechanism,49 and the distinction is not always clear. For example the purported S,1 protolysis of dibenzylmercury has been reinterpreted as a homolytic reaction with oxygen,50 and it has been suggested that the exchange of organic groups between Hg” and Hgo might involve an electron-transfer process rather than a four-centre mechanism.Equilibrium constants for the reaction R,Hg + R’,Hg + 2RR’Hg show that thedistributionofthealkylgroups Rand R’may vary widely fromrand~mness.’~ The kinetics of the acidolysis of allylmercuric iodides3 and of 4-pyridiomethyl-mercuric chloride have been studied ;54 it is proposed that in water the latter reaction follows a 1-and 2-anion-catalysed SEl mechanism. Acidolysis of dibenzylmercury and of benzyldihydroxyborane is accompanied by rapid deuteriodeprotonation of the aromatic ring which was ascribed to activation of the ring by hyperconjugative electron release from the metal-carbon bond.55 Mercuric salts are unique in bringing about the rapid oxymetallation of an olefin e.g.Hg(OAc) + MeOH + CH2=CH -+ AcO-CH,*CH,*OMe + AcOH In the presence of nitrite ion the products are p-nitroalkylmercuric com- pounds rather than P-mercurialkyl nitrites. 56 1,2-Dienes in methanol have been shown to undergo 2-mercuri-l-methoxylation.57 The rapid oxymercuration of an olefin and the reductive cleavage of the carbon-mercury bond in situ by sodium borohydride provides a very rapid and convenient method for the Markownikov hydration of an olefin.” The *’ A. J. Bloodworth and A. G. Davies J. Chem. SOC.,1965,6858. 46 N. K. Hota and C. J. Willis J. Organornetallic Chem. 1967,9 169. *’ E. C. T. Gevers Rec. Trav. chim. 1967,86,572; J. G. Noltes and J. Boersma J. Organometallic Chem. 1967,9 1. *’ 0.A. Reutov Russ.Chem. Rev. 1967,36 163. 49 K. C. Bass Organometallic Chem. Rev. 1966,1 391. ’O B. F. Hegarty W. Kitching and P. R. Wells J. Amer. Chem. SOC.,1967,89,4816. ” M. M. Kreevoy and E. A. Walters J. Amer. Chem. SOC.,1967,89,2986. s2 G. F. Reynolds and S. R. Daniel Inorg. Chem. 1967,6,480. ” M. M. Kreevoy D. J. W. Goon and R. A. Kayser J. Amer. Chem. SOC. 1966,88 5529; M. M. Kreevoy T. S. Straub W. V. Kayser and J. L. Melquist J. Amer. Chem. SOC. 1967,89 1201. ’* J. R. Coad and M. D. Johnson J. Chem. SOC.(B) 1967,633. ” W. Hanstein and T. G. Traylor Tetrahedron Letters 1967,4451. ” G. B. Bachmann and M. L. Whitehouse J. Org. Chem. 1967,32,2303. 57 R. K. Sherma B. A. Shoulders and P. D. Gardner J. Org. Chem. 1967,32,241. ” H. C. Brown and P. Geoghegan J.Amer. Chem. SOC. 19;67,89,1522; H. C. Brown and W. J. Hammer ibid. p. 1524; H. C. Brown J. H. Kawakami and S. Ikegami ibid. p. 1525. Alwyn G. Davies reactions are carried out at room temperature under very mild conditions which avoid rearrangement in the alkyl groups and are complementary to the hydroboration route for anti-Markownikov hydration (see below). NaBH, 'C=C' + Hg(OAc) + H,O -,-A-A--&-A /\ I1 Hg OH Some products and yields are given in the following equations. BuCH=CH BuCH(OH)CH (96%) PhCH=CH2 + PhCH(OH)CH (96%) cis-MeCHeHEt -* MeCH(OH)CH,.Et (65%) + MeCH,CH(OH)Et (35%) norbornene 4 fiorbornanol 100"4 yield > 99.8 % em) Cycloalk-2-en- 1-01s give stereospecifically the tr~ns-1,3-diols.~~ In the past few years there has been much interest in the use of phenyl(tri-ha1ogenomethyl)mercury compounds as sources of dihalogenocarbenes by the reaction Phenyl( tribromomet hy1)mercury and phenyl(dibromoch1oromet hy1)mercury (giving PhMgBr and :CC12) react readily in boiling benzene ;phenyl(trich1oro-methy1)mercury is much less reactive but all the reactions are catalysed by iodide ion.This availability of a dihalogenocarbene unit under mild conditions is useful in synthesis and is being exploited by D. Seyferth and his collaborators who have published a review.60 Reactions which have been studied during the current year are as follows C=C -,b-C-bX2;61 HCl -,HCXzC1;62 ROH -,[RO*CHC1,];63 Et,N + Et,N.CCI:CCI ;64 (Me,M),Hg -,Me,M.CCI:CC1,;65 Ph,MH -+ Ph,M.CX,H (M=Si or Ge);66 Me,Sn-SnMe -+ Me3Sn.CC'l,.SnMe3 ;67 59 S.Moon and B. H. Waxman Chem. Comm. 1967,1283. 6o D. Seyferth M. E. Gordon J. Y.-P. Mui and J. M. Burlitch J. Amer. Chem. SOC. 1967 89 959 ;D. Seyferth Proc. Robert A. Welch Foundation Conferences on Chemical Research. IX. Organo-metallic Compounds Robert A. Welch Foundation Houston Texas U.S.A. 1966 pp. 89-135. " D. Seyferth J. Y.-P. Mui and J. M. Burlitch J. Amer. Chem. SOC. 1967,89,4953. D. Seyferth J. Y.-P. Mui L. J. Todd and K.V. Darragh J. Organometallic Chem. 1967,8,29. 63 D. Seyferth V. A. Mai J. Y.-P. Mui and K. V. Darragh J. Org. Chem. 1966 3,4079. 64 D. Seyferth M. E. Gordon and R. Damrauer J. Org. Chem. 1967,32,469. 65 D. Seyferth R. J. Cross and B. Prokai J. Organometallic Chem. 1967,7 P20. 66 D.Seyferth J. M. Burlitch H. Dertouzos and H. D. Simmons J. Organomerallic Chem. 1967 7.405. 67 D. Seyferth and F. M. Armbrecht J. Amer. Chem. SOC. 1967,89,2790. '* D. Seyferth R. Damrauer and S. S. Washburne J. Amer. Chem. SOC.,1967,89 1538. Organometallic Compound 227 Group In.-Boron. Two excellent summaries of organoboron chemistry have appeared,69* 70 together with reviews on the carborane~,~ and on boron- nitrogen and boron-phosphorous compound^.^ About 10 years ago73 it was shown that diborane B2H6 which is readily available from for example sodium borohydride and boron trifluoride would add rapidly to olefins in ethereal solvents to give alkylboranes in which the the boron is carried by the less alkylated carbon atom. These organoboranes serve as very useful intermediates in organic synthesis.Above about 160” tertiary or secondary alkyl boranes rearrange to primary alkylboranes and the rearranged or unrearranged compounds can for example be treated with alka- line hydrogen peroxide to give alcohols with carboxylic acids to give alkanes or with olefins to give alkenes. The early work is summarised in ref. 74. The hydroboration of a hindered olefin may proceed only to the stage of a mono- or di-alkylborane; three products of this type which have their own specific applications in synthesis are (from cyclohexene) dicyclohexylborane (C,H BH ; (from trimethylethylene) bis-( 1,2-dimethylpropyl)borane[(6); ‘di-s-iso-amylborane’ or ‘disiamylborane’]; and (from tetramethylethylene) 1,1,2-trimethylpropylborane[(7); ‘t-hexylborane’ or ‘the~ylborane’].~’ (HMe,C-CHMe),BH (6) Me2CH*CMe,*BH2 (7) This continues to be an active and productive field.Most of the emphasis is still on developing new or improved synthetic methods but some papers have dealt with the mechanisms of the reactions. Electron withdrawal by X in ring-substituted styrenes XC6H4*CH<H2 slightly activates attack of boron at the a-position and deactivates attack at the f3-position which is consistent with the reactions proceeding through 4-centre transition states (8) and (9).’,9 77 If a dialkylborane is prepared by hydroboration of an optically active olefin (e.g. a-pinene) the addition of a third (inactive) olefin can occur with induction 6-6+ 6+ 6-6+ 6-6-6+ (8) (9) (10) 69 M.F. Lappert ‘The Chemistry of Boron and its Compounds,’ ed. E. L. Muetterties Wiley New York ch. 8. ’O Ref. 4 pp. 177-295. R. Kiister and M. A. Grauberger Angew. Chem. Internat. Edn. 1967,6 218. ’’ H. Steinberg and R. J. Brotherton ‘Organoboron Chemistry. Boron-Nitrogen and Boron- Phosphorus Compounds,’ Interscience New York 1967. 73 Ann. Reports 1957,54 188,193. 74 H. C. Brown ‘Hydroboration,’ Benjamin New York 1962. 75 E.g. H. C. Brown and E. Negishi J. Amer. Chem. SOC.,1967,89,5478. ’‘ J. Klein E. Dunkelbaum and M. A. Wolff J. Organometallic Chem. 1967,7 377. ” H. C. Brown and R. L. Sharp J. Amer. Chem. SOC. 1966,88,5851. H* Alwyn G. Davies of asymmetry,78 of a chirality which implies a triangular (10) rather than a rectangular [e.g.(8) or (9)] transition state.79 The rearrangement of the model compounds Bu'BBu', Pr',B,and Bu",B to the appropriate primary alkylboranes are all first-order kinetically. The rates suggest that rearrangement of the t-butyl group involves complete elimination ofthe B-H bond which then adds back in the opposite sense but the (reversible) rearrangement of the isopropyl and s-butyl groups may involve separation of the B-H and olefin fragments only to the degree of a 7c-complex.'' The migration of a boron atom to the end of a carbon chain involves a pro- gression of such addition-elimination processes. The reactions provide an easy route to w-cycloalkyl-cl-alkanols8 and o-cycloalkyl-a-alkenes,82 e.g. IB... B B- A If it is difficult to displace the alkene from the alkylborane (e.g.from triethyl- borane or tri-em-norbornylborane) with decene ; an aldehyde may be used instead.83 At temperatures above those which the alkylboranes isomerise they may eliminate an olefin and hydrogen to give a heterocyclic borane. Aralkylboranes can undergo a similar cyclisation by eliminating an alkane,84 e.g. A number of new reagents (X-Y of varying charge type) have been developed for cleaving the boron-carbon bond. All these like hydrogen peroxide probably react by initial nucleophilic attack of X at boron followed by nucleophilic '' D. R. Brown S. F. A. Kettle J. McKenna and J. M. McKenna Chem. Comm. 1967,667. 79 A. Streitwieser L. Verbit and R. Bittman J. Org. Chem. 1967,32 1530.F. M. Rossi P. A. McCusker and G. F. Hennion J. Org. Chem. 1967,32,450. H. C. Brown and G. Zweifel J. Amer. Chem. SOC.,1967,89,561. H. C. Brown M. V. Bhatt T. Munekata and G.Zweifel J. Amer. Chem. SOC.,1967,89,567. 83 B. M. Mikhailov Yu. N. Bubnov and V. G. Kiselev J. Gen. Chem. (U.S.S.R.),1966,36,65. " R. Koster G. Benedict W. Fenzl and K. Reinert Annalen 1967,702,197. Organometallic Compouncis 1,2-rearrangement of an alkyl group from B to X displacirlg the good leaving group Y. This would be expected to give retention of configuration in R and the cleavage of di-isopinocampheyl-s-butylborane(from B2H6 a-pinene and cis-but-2-ene) with hydrogen peroxide to’ give (R)-s-butyl alcohol and with hydroxylamine- 0-sulphonic acid (NH2-O*S02*OH) to give (R)-s-butylamine has been used to correlate the rotatory power and configurations of these product^.^' Trimethylamine oxide (ONMe,) quantitatively oxidises a wide range of arganoboranes to alkoxyboranes and may have some advantages over alkaline hydrogen peroxide for example for base- or oxygen-sensitive boranes.The ylids CH &Me,,86 CH * 6Ph,,87 and CH iMe288 have been added to those already available (CH -G2and CH -iMe,O) for introducing a CH residue into an R-B bond. A major development in the use of organoboranes in organic synthesis makes use of their reaction with carbon monoxide,89 which will take place at room temperature in an ethereal solvent such as diglyme. The mechanisms of the reactions which occur have not been fully established but they can be reationalised in the following scheme which involves sequential migration of each of the three alkyl groups from boron to carbon.R R R 1 R3BTR2$-C0 + RCCR + kCR + 211 \/ 00 1 OOH3 HO CHzR RB(0H)- CR OH HO * CR3 (13) 1 OOH OXR2 (12) Olefin Yield (%) R(-W R RCH2*OH R,CO R,C-OH But-1-ene Bun 72 85 90 But-2-ene Bus 81 87 Cyclohexene Cyclohexyl 80 80 80 N orbornene exo-N orbornyl 85 82 80 85 L. Verbit and P. J. Hefion J. Org. Chem. 1967 32,3199 86 W. K.Musker and R. R. Stevens Tetrahedron Letters 1967,995. 87 R. Koster and B. Rickborn J. Amer. Chem. SOC.,1967,89,2782. J. J. Tufariello P. Wojtkowski and L. T. C. Lee Chem. Comm. 1967,505. B9 M. E. D. Hillman J. Amer. Chem. SOC.,1962,84,4715; 1963,85,982 1626.230 Alwyn G.Davies First if the trialkylborane R3B in diglyme is treated with carbon monoxide at 1 atm. and 100-125" 1 mol. is absorbed and the product after oxidation with hydrogen peroxide gives the tertiary alcohol (13). The yield is often im- proved by adding glycol which perhaps stabilises the final boronic anhydride as its glycol ester. Some yields are given in the Table.go Secondly if the carbonylation is carried out in the presence of water migration of the third alkyl group is inhibited perhaps by hydrolytic ring-opening of the bora-epoxide. Oxidation then give the ketone (12) as shown in the Table.g1 Thirdly if sodium borohydride or lithium borohydride is present during the carbonylation migration can be restricted to the first alkyl group :the reaction now takes place more readily and 1 mol.of carbon monoxide is absorbed at 45" in 1 hr. and the primary alcohol (11) can be isolated in good yield (see Table).92 The three alkyl groups migrate intramolecularly. No crossed products are formed when a mixture of triethylborane and tributylborane is carbonylated and the mixed dicyclohexyl- 1-octylborane (R,R'B) (from dicyclohexylborane and oct-1-ene) gives the single mixed tertiary alcohol (R,R'C-OH). The dicyclohexylboranes prove to be remarkably reactive and can be car- bonylated at 45" in tetrahydrofuran. Under these conditions the mobility of the cyclohexyl group is low and for example dicyclohexyloctylborane gives an 86% yield of ketones consisting of 92% of cyclohexyl octyl ketone and 8 % of dicyclohexyl ketone.93 The reactions are tolerant towards many func- tional groups (e.9.0-CO-Ph CO-OMe C=N) providing a route to func- tionally-substituted cyclohexyl ketones and as the cyclohexyl group has a high mobility in a Baeyer-Villiger oxidation with a peroxy-acid these ketones may then be converted into the corresponding functionally-substituted alkanecar- boxylic acids,94 e.g. CH2=CH -[CH2l8 .C02Me + 0x0* [CH,] * COzMe RCO H 2H0,~C[CH2]lo.C02Me CH,<H. [CH,] *CH2 *OH + -CO-[CH,] lo*CH2 .OH RC035 H02C* [CH,] * CH OH The 1,1,2-trimethylpropyl group has an unusually low mobility in the car- bonylation step and boranes carrying this group react readily with carbon monoxide only at 60 atm.pressure. Under these conditions two olefins can be linked through a carbonyl group to give mixed ketones by the process 90 H. C. Brown and M. W. Rathke J. Amer. Chem. SOC. 1967 89 2737; H. C. Brown and E. Negishi J. Amer. Chem. SOC.,1967,89 5478. 91 H. C. Brown and M. W. Rathke J. Amer. Chem. SOC.,1967,89,2738. 92 M. W. Rathke and H. C. Brown J. Amer. Chem. SOC.,1967,89,2740. 93 H. C. Brown and M. W. Rathke J. Amer. Chem. SOC.,1967,89,4528. " H. C. Brown G. W. Kabalke and M. W. Rathke J. Amer. Chem. SOC.,1967,89,4530. Organometaiiic Compounds 231 HBH2 olefin sB/R olefin? \H R I O==C' =-w-"' 'R' OH OH Two examples are as follows.95 Dienes can be converted into cyclic ketones by a similar pro~ess.'~ c -o$<-0=3 (78%) In most of the work described in this section the proof of structure of the organoboranes is based on the premise that alkaline hydrogen peroxide always brings about hydroxydeboration with complete retention of configuration in the alkyl group.An interesting possible exception to this rule has appeared in the diboration of alkenes and alkynes with diboron tetrachloride. The common factors between the infrared and Raman spectra show that the adduct between B2C14 and acetylene is cis-Cl,B* CH :CH BC12;97 simi-larly the adduct with but-2-yne is cleaved by base to give cis-but-2-ene. Again the adduct formed by cis-but-2-ene and by trans-but-2-ene is oxidised by hydro- gen peroxide to rneso-and (f)-butane-2,3-diol respectively and the adduct from cyclohexene give cis-cyclohexane- 1,2401.~~ All these diborations are therefore assumed to occur in a cis-sense.Cyclopentene however reacts with B,C14 to give after hydroxydeboration trans-cyclopentane- 1,2-diol; either the diboration must occur in a trans-sense or the hydroxydeboration must give retention of configuration at one site and inversion at the other.99 The 1-or 2-halogenoalkyl-boranes (R,B) or borates (R4B-) can be prepared 95 H. C. Brown and E. Negishi J. Amer. Chem. SOC. 1967.89.5285. 96 H. C. Brown and E. Negishi J. Amer. Chem. SOC.,1967,89 5477. 97 R. W. Rudolph J. Amer. Chem. SOC.,1967,89,4216. 98 M. Zeldin A. R. Gatti and T. Wartik J. Amer. Chem. SOC. 1967.89,4217. 99 H. K. Sahar L. J. Glicenstein and G. Urry,J. Organometallic Chem.1967,8 37. Alwyn G. Davies by hydroboration of a halogeno-alkene or -alkyne or by halogenation of an alkenyl- or alkynyl-borane or by halogeno-alkylation of an alkylborane. These compounds may then react in the following three ways. (1) trans-l,2,Elirnina- tion of R,B-X (X = halogen) under solvolytic conditions. (2) cis-1,2-Elimina- tion of R,B-X under thermolytic conditions. (3) Nucleophilic 1,Zmigration of a group R from boron to carbon displacing X with inversion at the carbon centre. The potential of these reactions in organic synthesis is being investigated ; some parallel work on organoaluminium compounds is described in a later section. But-1-yne reacts with diborane to give a mixture of polymeric 1,l- (mainly) and 1,2-diboroalkane~,'~~ but a dialkylborane such as dicyclohexylborane"' or bis-( lY2-dimethylpropyl)boraneadds to give a vinylborane (14) Bu I -Bu\C..,c<H -(18) IJNaOH "%c'+qc\\\\\\ BuCECH R,BH H0 BBr HI b-R I R Bu Br Bu R (16) (17) (19) trans-Addition of bromine to the double bond then gives the erythro- dibromide (1 5) which undergoes trans-dehalogenoboration to the cis-vinyl bromide (16).Thermal decomposition of the dibromide on the other hand brings about cis-dehalogenoboration to the trans-vinyl bromide (17). Phenyl-acetylene is exceptional in that the solvolytic route gives the trans-bromide and the thermolytic route the cis-isomer.'" Iodine on the other hand does not give a vinyl iodide when it reacts with the vinylborane (19).Under alkaline conditions an alkyl group migrates from boron to carbon perhaps in the iodonium ion (18) then trans-deiodoboration loo G. Zweifel and H. Arzoumanian J. Amer. Chem. SOC.,1967,89,291. G. Zweifel H. Arzoumanian and C. C. Whitney J. Amer. Chem. SOC.,1967,89,3652. lo' H. C. Brown D. H. Bowman S. Misumi and M. K. Unni J. Arner. Chem. SOC.,1967,89,4531. Organometallic Compounds leads to the cis-olefin (19) in 81 %yield. A route is thus available for stereo- selectively introducing an olefinic side-chain on to both acyclic and cyclic systems. O1 Similar rearrangement and elimination reactions occur in the halogeno- alkyl- and halogenoalkenyl-boranes obtained from the hydroboration of alkenyl and alkynyl halides. Polyhalogenated ethylenes and propenes are completely dehalogenated by a sequence of hydroborations and dehalogeno- borations to give ultimately alkylb~ranes,"~ but the adducts of vinyl chlordes or bromides with dicyclohexylborane rearrange providing a route to the secondary alcohols (20).OH (20) The adducts of iodoalkynes [e.g.(21)] do not rearrange in tetrahydrofuran and acidolysis gives the product of cis-hydrogenation. Nucleophiles such as methoxide ion however convert the borane into a borate complex which does rearrange and can then be converted into a variety of functional derivatives such as (22) and (23).'04 Bu \ BUCXI l)zBF 'cx -BU c==c ,B(C6Hl ,)OMe \ H' cBCsHl1 H' C6H 11 (21) C6Hll ( I/OMe \,,,; ki RCO,H Bu Bu H BUCH2 *CO *C6 Hi 1 \/ \Cd' C==C \ H' H H '(22) 'C6H 11 (23) A similar rearrangement also occurs in the a-halogenoalkenyl- and a-halogenoalkyl-boranes which are formed when triphenylborane is treated with the appropriate organolithium reagent,"' and in the ylid which appears to result from treating a triethylpropynyl borate with an acyl chloride.lo6 lo3 R.Koster and W. Fenzl Angew. Chem. Internat.Edn. 1967,6 802. lo4 G. Zweifel and H. Arzoumanian J. Amer. Chem. SOC. 1967,89 5087. G. Kobrich and H. R. Merkle Angew. Chem Internat. Edn. 1967 6 74; Chem. Ber. 1967 100,3371. P. Binger Ancgew. Cheni. Ilrrerrlur. Edii. 1967 6 84. Alwyn G. Davies Aluminium.From the theoretical point of view organoaluminium compounds are interesting because of their unusual structure ;from the practical standpoint they are important because they can be prepared cheaply and will take part in a number of novel and useful reactions.Both aspects have received attention during the past year. Whereas organoboranes are monomeric trimethylaluminium has a structure like diborane in which two methyl groups bridge two approximately tetra- hedrally hybridised aluminium atoms (24; R = R' = Me).'07 In hydrocarbon solvefits at -75" the 'H n.m.r. spectrum shows the presence of distinct terminal and bridging groups but at room temperature a single signal is observed because of the rapid exchange of the methyl groups. (24) The crystal structure has been redetermined,lo8 and the hydrogen as well as the aluminium and carbon atoms have been located confirming the above picture.Crystalline triphenylaluminium is a similar centrosymmetric dimer (24; R = R' = Ph) with considerably distorted bridging phenyl groups (R') which are twisted at an angle of 84.4"with respect to the central ring,lo9 and the low-temperature n.m.r. spectrum shows that in dimethylphenylaluminium it is the phenyl rather than the methyl groups which are involved in bridging (24; R = Me R' = Ph).'" Triethylaluminium is similarly a bridged dimer and the rate of uptake of ethylene by (C2D,),A12 shows that the hydrogen atoms do not participate in bridge-bonding by tunneling.' '' In the crystalline complex (Me3A1)2C4Hs02 dioxan is in the chair form with each oxygen co-ordinated to a Me,AI unit which is nearer trigonal than tetra- hedral.Much of the synthetic utility of boron compounds depends on the ability of only a boron-hydrogen bond to add (reversibly) to a C=C or C=C bond. With aluminium both the A1-H and Al-C bonds can add again reversibly the latter process leading by replication to the oligomerisation or polymerisation of ethylene and a combination of the two processes leading to the dimerisation of higher olefins. Hitherto trialkylaluminium compounds have usually been used in conjunc- tion with olefins often in catalytic reactions. The dialkylaluminium hydrides are now finding increasing use often in conjunction with acetylenes and in lo' P. H. Lewis and R. E. Rundle J. Chem. Phys. 1953,21,986. lo' R. G. Vranke and E. L. Amma J. Amer. Chem. SOC.1967,89,3121. J. F. Molone and W. S. McDonald Chem. Comm. 1967,444. 'lo E. A. Jeffery T. Mole and J. K. Saunders Chem. Comm. 1967 697. l1 ' K. H. Reichert and H. Sinn J. Organometallic Chem. 1967 7; 189. '" J. L. Atwood and G. D. Stucky J. Amer. Chem. SOC. 1967,89,5362. Organometallic Compounris non-catalytic procedures. Much of this is parallel to the work described above involving organoboron hydrides and is being carried out by the same groups of investigators. Hexa-1,5-diene reacts with diethylaluminium hydride with ring-closure but if the reaction is carried out with diethylaluminium hydride etherate the initial hydroalumination is much faster than any subsequent intramolecular organo- alumination and the a-aluminohexene (25) is formed.If a trace of triethyl- aluminium is now added this removes the ether and the aluminomethylcyclo- pentane is again formed.’ ’ I I5 Et,Al ,0Et2 + HAlEtz A dialkylalumium hydride reacts with an alkyne by cis-addition to give a vinylalane (26) ;various halogens (Br2 ICl 12)now cleave the carbon-aluminium bond with retention of configuration giving the pure trans-vinyl halide ;’l4 only bromide reacted in this way with the corresponding vinylborane (14). Methyl-lithium converts the vinylalane into the ate complex (27) which brings about vinylation with retention of configuration ; for example carbon dioxide gives trans-hex-2-enoic acid (28) and formaldehyde gives the corres- ponding alcohol (29).’ ’’ Bu Bu BuCdH Bu,’AIH+ \c_c/H -*2 ‘c=c /H /\ H AlBu ‘x H’ MeLi Bu H Bu Bu H ‘C=d H / ‘CH -OH y-I@ H ;c=c /H AIBui,Me co2 H’‘c=c’ ‘C0,H -(29) (27) (28).R. Reinlcker and G. F. Gothel Angew. Chem. Internat. Edn. 1967,6,872. ‘14 G.Zweifel and C. C. Whitney J. Amer. Chem. SOC. 1967,89,2753. G. Zweifel and R. B. Steele J. Amer. Chem. SOC.,1967,89 2754. Alwyn G.Davies In contrast lithium di-isobutylmethylaluminiumhydride reacts with an alkyne apparently by trans-addition providing a route to derivatives of the trans-oIefin,"6 e.g. R H R AIBui,Me /' R I RMR Li(Bui2MeAlHL '-/ 12 H /\ R \ H /" \R (R = Me or Et) The organic compounds of gallium indium and thallium have been re-viewed.' '' Group 1V.-Preparative and structural problems appear to be less acute in Group IV which is being used as a field for developing and testing theories of constitution and mechanism.The ethynyl' 18*' l9 and the organosulphur'20 derivatives of silicon ger-manium tin and lead have been reviewed and the second edition of Dub's register of the organic compounds of germanium tin and lead has been pub-lished.' ' Silicon. Reviews have been published on carbosilanes,'22 oligo-and poly-siloxane~,'~~ ~ilanes,'~~ siloxy-compounds of transition metals,'25 and organohalogenosilanes. Gilman's group have continued their work on silicon-silicon bonded Com-pounds which are usually prepared by a Wurtz-Fittig reaction on a halogeno-silane. They have prepared the compounds (Me,Si),Si (60-70 % yield),12' C6C1,Si(SiMe3)3,'28 and (Me3Si)3Si-Si(SiMe3)3'29by this procedure and '16 G.Zweifel and R. B. Steele J. Amer. Chem. SOC. 1967,89 5085. K. Yasuda and R.Okawara Organometallic Chem. Rev. 1967,2,255. "'W. E. Davidsohn and M. C. Henry Chem. Rev. 1967,67 73. '19 L. K. Luneva Uspekhi Khim. 1967,36,1140. 120 E. W. Abel and D. A. Armitage Ado. Organornetallic Chem. 1967,5 1. 12' 'Organometallic Cornpoi-rids. 11. Germanium Tin and Lead,' ed. M. Dub 2nd edn. ed. R. W. Weiss Springer Berlin 1967 [vol. I (1966) covered the transition metals.] G. Fritz Angew. Chem. Internat. Edn. 1967,6,677. 123 G. Schott Fortschr. Chem. Forsch. 1967,9,60. lZ4 E. Hengge Fortschr. Chem. Forsch. 1967,9 145. F. Schindler and H. Schmidbaur Angew. Chem. Internat. Edn. 1967,6,683. lZ6 R.J. H. Voorhoeve 'Organohalosilanes.Precursors to Silicones,' Elsevier Amsterdam 1967. 12' H. Gilman and L. C. Smith J. Organometallic Chem. 1967,8 245. 12' H. Gilman and K.Shiina J. Organometallic Chem. 1967,8,369. 129 H. Gilman and R. L. Harrell J. Organometallic Chern. 1967,9 67. 0rganome tal lic Compounds 237 compounds Cl(Ph,Si),Cl and Cl(Ph,Si),Cl by ring-opening of the correspond- ing tetra- and penta-silanes.I3O The silacyclobutanes are interesting because ring-strain enhances the reac- tivity of the Si-C bond. Silacyclobutane itself has been prepared; in the mass- spectrometer it loses ethylene giving the radical ion H2h * CH as the strongest peak.' ' 1,l-Dimethylsilacyclobutanesimilarly loses ethylene at 4W forming 1,1,3,3-tetramethyl-1,3-disilacyclobutane;the dissociation is inhibited by propene or ethylene and water completely suppresses the formation of the disilacyclobutane giving trimethylsilanol and hexamethylsiloxane.It was suggested that these results implied dissociation to ethylene and the molecule Me,SiCH, which if it is not a diradical is the first evidence for the existence of a silicon-carbon double bond.' 32 Me ,Si-CH , II Me,Si--CH, I I + CH,==CH2 + Me2Si==CH2/CH2-siMe2 CHZXH -%6'-Me,SiOH The first insertion of dichlorocarbene into a carbon-silicon bond has been reported for dimethylsilacyclobutane,68 and the compounds R3Si* [CH,] -GeBu,H R,Si*[CH,] *GeBu [CH,] *GeBu,H and Et3Ge[CH,] -GeBu,H have been prepared by the ring-opening of 1,l-dibutyl- germacyclobutane with the appropriate silicon or germanium hydride in the presence of chloroplatinic acid.' 33 Corey and Seebach's route to ketones2 has been extended to the preparation of some trialkylsilyl and trialkylgermyl ketones (e.g. Me,% -CO. Me Ph,Ge. CO- Me Et,Ge *CO-GeEt, Me3Si*CO-GeEt,).134' ' 35 The silyl ketones absorb strongly at 380-420cm.-' and are photolysed in alcohols to give silyl acetals with retention of configuration in the trialkylsilyl group ; the reaction may involve insertion of a siloxycarbene into the OH bond of an alcohol.' 36 Electrophilic rearrangement of the silyl group from carbon to oxygen giving ultimately a siloxyalkene may also occur when the silyl ketone is treated with diazomethane or with triphenylmethylenephosphoranes.'37 (Y R,Si.CO -R' % R,Si-C-R' + R,Si 0.C-R' =% R,Sj -0 .CHR'. OR" u H. Gilman and D. R. Chapman J. Organometallic Chem. 1967,8,451. L. Laane J. Amer. Chem. SOC.,1967,89 1144. 132 L. E. Gusel'nikov and M. C. Flowers Chem. Comm. 1967,864. 133 P. Mazerolles J. Dubac and M. Lesbre Tetrahedron Letters 1967 255. 134 E. J. Corey D. Seebach and R. Freedman J. Amer. Chem. Soc. 1967,89,434. 13' A. G. Brook J. M. Duff P. F. Jones and N. R. Davis J. Amer. Chem. SOC. 1967,89,431. 136 A. G. Brook and J. M. Duff J. Amer. Chem. SOC.,1967,89,454. 137 A. G. Brook W. W. Limburg D. M. McRae and S. A. Fieldhouse J. Amer. Chem. SOC. 1967 89.704. Alwyn G.Davies Sommer's resolution in 1959,' 38 of methyl-1-naphthylphenylsilaneinitiated a series of papers on the stereochemistry ofreactions occurring at the silicon centre.Some other optically active alkylmethylphenylsilanes (RMePhSiX; R = Et Ph2CH Me,C*CH,) have been prepared,'39 and the first disilane Ph3Si SiMePhX has been resolved.'40 Good leaving groups X,such that the pK of HX < 6 (e.g. X = C1 OAc) are displaced by a more basic nucleophile with inversion of configuration probably through a bipyramidal transition state (as for an S,2 reaction at carbon) or intermediate (cf. Me,PF,).14,' Organolithium or organomagnesium reagents however may displace fluorine with retention perhaps by an SNi rea~ti0n.l~~ Less-good leaving groups such as OR H,14 NR2,144 or SR14' are more prone to give retention. Various Group VIII metals have been evaluated in catalysing the reaction R3SiH + HX + R,SiX + H2 for preparing silylamines silanethiols and halogeno~ilanes.'~~ Like the corresponding reactions of hydroxylic com- pound~,'~' many of these reactions proceed with inversion and cannot follow a simple 4-centre mechanism involving adsorbed hydrogen The same catalysts also promote the exchange of hydrogen in the systems H,/R3SiD and R,SiH/R,SiD and catalyse the addition of R,SiH to an olefin; these re- actions now involve retention of configuration at silicon.148 1,2,3,4-Tetrahydro-2-methoxy-2-ol-naphthyl-2-silanaphthalene has also been resolved and shown to undergo many reactions at the asymmetric silicon centre with a high degree of retention of optical purity but the relative configurations of the reactants and products are not yet known.149 Germanium.Organoaluminium compounds have little advantage over Grignard reagents for alkylating germanium tetrachloride,' 50 but tetra-alkyl-lead compounds may be useful for bringing about mono- and di-alkyla- tion.' ' Arylhalogenogermanes can be prepared from the reaction between germanium tetrachloride and tetraphenylgermane in the presence of alu- minium chloride," ' or between germanium tetrachloride and aryl iodides in the presence of copper powder.'52 '" L. H. Sommer 'Stereochemistry Mechanism and Silicon,' McGraw-Hill New York 1965. 13' L. H. Sommer K. W. Michael and W. D. Korte J. Amer. Chem. SOC.,1967,89,868. ''O L. H. Sommer and K. T. Rosborough J. Amer. Chem. SOC.,1967,89 1756. L. H.Sommer G. A. Parker N. C. Lloyd C. L. Frye and K. W. Michael J. Amer. Chem. SOC.,1967,89 857. L. H. Sommer W. D. Korte and P. G. Rodewald J. Amer. Chem. Soc. 1967,89,862. 14' L. H. Sommer and W. D. Korte J. Amer. Chem. Soc. 1967,89,5802. 14' L. H. Sommer and J. D. Citron J. Amer. Chem. Soc. 1967,89,5787. L. H. Sommer and J. McLick J. Amer. Chem. SOC. 1967,89,5806. L. H. Sommer and J. D. Citron J. Org. Chem. 1967,32,2470. 14' L. H. Sommer and J. E. Lyons J. Amer. Chem. SOC.,1967,89,1521. L. H. Sommer J. E. Lyons H. Fujimoto and K. W. Michael J. Amer. Chem. SOC.,1967,89 5483; L. H. Sommer K. W. Michael and H. Fujimoto ibid. 1967,89 1519. 14' R. J. P. Corriu and J. P. Masse Chem. Comm. 1967 1287. F. Glocking and J. R. C. Light J. Chem. Soc. (A),1967,623.lS1 K. Kiihlein and W. P. Neumann Annalen 1967,702 17. lS2 V. F. Mironov and N. S. Fedotov J. Gen. Chem. (U.S.S.R.),1966,36 574. OrganometallicCompounds Trichlorogermane reacts with ketones containing a primary alkyl group condensation and dehydration is followed by addition of the germane to the double bond to give a p-trichlorogermylketone in very good yield e.g. 2 If the ketone R,CO cannot condense the corresponding alkyltrichloro- germane RzCH GeCl, is formed probably through the alcohol RzCH*OH.153 Tris(trimethylgermy1)-arsine and -phosphine have been prepared.’ 54 The Ge-0 bond in tributylmethoxygermane and dributylethoxygermane has been shown to add to the doubly-bonded systems in phenyl isocyanate phenyl isothiocyanate chloral and di-p-tolyl carbodi-imide :’’’it is thus less reactive than the Sn-0 or Pb-0 bonds but more reactive than the Si-0 bond.Tin. An excellent monograph (in German) on organotin chemistry has been published by W. P. Neumann,’” and is to be translated into English. It gives a particularly good account of the organotin hydrides which are largely omitted from this report.”* The following topics have also been reviewed structural aspect^"^ and co-ordination number ;I6’ bivalent compounds and hydrostannolysis.’62 Organotin compounds lend themselves to spectroscopic studies because the lI9Sn isotope has a nuclear spin of 3 and the “’“Sn isotope decays emitting a y-ray which can be used in Mossbauer spectroscopy.163 Some of the simple correlations which were drawn between spectra and structure have not stood up to closer examination.Heteronuclear double resonance is clearly going to be a powerful technique for studying the organic derivatives of many metals. By this method it has been shown that in compounds containing the structure H-C-Sn a plot 153 0.M. Nefedov S. P. Kolesnikov and B. L. Perlmutter Angew. Chem Internat. Edn. 1967,6 628. lS4 I. Schumann and H. Blass 2. Naturforsch. 1967,22b 1105. 15’ Y. Ishii K. Itoh A. Nakamura and S. Sakai Chem. Comm. 1967,224. lS6 Ann. Reports 1965,62,289; 1966,63,371; cf. L. Birkofer,F. Miiller and W. Kaiser Tetrahedron Letters 1967 2781 ;A. J. Bloodworth A. G. Davies and S. C. Vasishtha J. Chem. SOC. (C) 1967 1309. Is’ W. P. Neumann ‘Die Organische Chemie des Zinns,’ Enke Stuttgart 1967.E. R. Birnbaum and P. H. Javora J. Organometallic Chem. 1967,9 379; K. Hayashi J. Iyoda and I. Shiihara ibid. 1967 . 81. lS9 R. Okawara and M. Wada Adv. Organometallic Chem. 1967,5 137. M. Gielen and N. Sprecher Organometallic Chem. Rev. 1966,1,455. 16’ J. D. Donaldson Prog. Inorg. Chem. 1967,8,287. H. M. J. Creemers ‘Hydrostannolysis. A General Method for Establishing Tin-Metal Bonds,’ Schotanus and Jens Utrecht 1967. R. H. Herber Progr. Inorg. Chem. 1967,8 1. 240 Alwyn G. Davies of J(ll9Sn-H) against J('19Sn-'3C) is linear but does not pass through the origin and the assumption that there is adirect correlation between J( 'I9Sn-H) and the s-character of the Sn-4 bond is not valid.164 The correlations between the Mossbauer isomer shift and the ionic bond character in organotin compounds which were based on a limited number of compounds break down when a wider range of compounds are tested.'65 The mass spectra of the organic derivatives of the Group IY metals are characterised by the near absence of the parent ion.As would be expected most of the positive ion current is carried by metal-containing species. Initially the compound R4M decomposes to the radical R' and the ion R3M+ which has the configuration of a third-group metal. Subsequent decomposition then follows the trend towards tervalence with aluminium and predominant univalence with thallium. 66 There is now a lot of evidence that functional organotin compounds for example R3SnX are frequently co-ordinated through the functional group X into polymers containing 5-co-ordinate tin.' 58 Trimethyltin formate ap-parently is usually a polymer of this type and is virtually insoluble in organic solvents.A second soluble form has now been prepared by heating the insoluble form in cyclohexane at 100" for several hours. In carbon tetra- chloride it is a trimer or tetramer; the infrared and n.m.r. spectra suggest that there is an equilibrium in solution between the monomeric and cyclic oligomer but both the soluble and insoluble forms can be sublimed without interconverting. 67 The exchange of functional groups X between different tin sites can be followed by n.m.r. spectroscopy. In the methyltin halides Me,SnX,_, Br/C1 exchange is always very fast Br/I exchange is slower and Cl/I exchange slower still whatever the value of n.The rate decreases as n decreases and is faster in chloroform than in carbon tetrachloride suggesting that the exchange might involve a five-co-ordinate transition state.'68 On the other hand the dependence on temperature of 19Sn-H coupling in stannylamines R,Sn(NR',),_, shows that the rate of symmetrical exchange of amino-groups increases as n decreases or as the size of the organic groups is reduced.'69 In dialkyltin(rv) compounds unsymmetrical exchange between R,SnX2 and R,SnY can give new compounds R,SnXY and a series of methoxides R,Sn(OMe)X have been isolated ;32* a similar reaction involving a poly- lti4 W. McFarlane J. Chem. Soc.(A) 1967 528 165 J.J. Zuckerman J. Inorg. Nuclear Chem. 1967 29 2191; M. Cordey-Hayes R. D. Peacock and M. Vucelic ibid. p. 1177; J. Nasielski N. Sprecher J. Devooght and S. Lejeune J. Organo-metallic Chem. 1967,8,97. 166 J. J. de Ridder and G. Dijkstra Rec. Trau. chim. 1967,86,737; D. B. Chambers F. Glockling and M. Weston J. Chem. Soc.(A) 1967 1759. 16' P. B. Sirnons and W. A. Graham J. Organometallic Chem. 1967,8 479; 1967 10,457;cf. Y. Maeda and R. Okawara J. Organometallic Chem. 1967,lO. 247. E. V. van der Berghe G. P. van der Kelen and Z. Eeckhaut Bull. SOC.chim. belges 1967,76 79. 169 E. W. Randall C. H. Yoder and J. J. Zuckerman J. Amer. Chem. SOC. 1967,89,3438. A. G. Davies and P. G. Harrison J. Chem. Soc.(C) 1967,1313. Organometallic Compounds 241 meric dialkyltin oxide (R2SnO),,17' or sulphide (R2SnS)3,172 and a second component R, SnX4_, gives functionally substituted distannoxanes or dis- substituted heterostannoxanes XR2Sn*0.M (M = Hg T1 Si Ge or Pb e.g.ClBu,Sn*O*HgPh ClMe,Sn*O*SiMeCl, and ClBu,Sn* O.PbBu,Cl) are formed when dialkyltin oxides are treated with derivatives of the other metals MX.173 These reactions may be regarded formally as the insertion of R,SnO or R2SnS units into the Sn-X or M-X bond and polymeric stannoxanes e.g. C1Bu,Sn(0SnBu2),,C1 and BuSn[(OSnBu,),Cl], have been isolated from the telomerisation reaction between dibutyltin oxide and the appropriate amount of dibutyltin dichloride or butyltin trich10ride.l~~ Mixed-metal Compounds.-This topic was discussed last year.75 The stretching frequencies of the Sn-M bonds (M = Sn Ge Mn Mo Fe Co) nave been identified in the infrared spectra.176 Compounds containing the following mixed metal-metal bonds have been discussed Li_Si,'77 Li-Ge,'77.178 K-Ge,179 Hg-Si,'77.1807 181 Hg-Ge,177. 178. 180 182 T1-Ge,178 Si-Ge,177. 178 Si-Sn,177 Ge-Sn,'77* 178* Si-Sb,'84 Ge-Sb,'84 Sn-Sb,'84* 185 Si-Te,'86 Ge-Te,lS6* lS7 Sn-Te.ls6 By the hydrostannolysis reaction germono-stannanes containing up to 8 catenated metal atoms have been prepared.162* Radicals derived from compounds of the type (R,M),Hg (M = Si or Ge) have been used for silylating the aromatic ring,lS1 and for disilating and digermylating C=C C=C and N=N groups.'80 171 A. G. Davies and P. G. Harrison J. Organometallic Chem.1967 7 P13. A. G. Davies and P. G. Harrison J. Organometallic Chem. 1967 8 P19; R. C. Poller and J. A. Spillman ibid. 1967 7 259. 173 A. G. Davies and P. G. Harrison J. Organometallic Chem. 1967 10 P31. 174 A. G. Davies P. G. Harrison and P. R. Palan J. Organometallic Chem. 1967,10 P33. 17' Ann. Reports 1966 63 371. -N. A. D. Carey and H. C. Clark Chem. Comm. 1967,292; H. Schumann and S. Ronecker 2. Naturforsch. 1967,22b 452. 177 N. S. Vyazankin G. A. Razuvaev E. N. Gladyshev and S. P. Korneva J. Organometallic Chem. 1967 7 353. 178 N. S. Vyazankin E. N. Gladyshev G. A. Razuvaev and S. P. Korneva J. Gen. Chem. (U.S.S.R.). 1966,36,969. E. J. Bulten and J. G. Noltes Tetrahedron Letters 1967 1443. K. Kiihlein W. P. Neumann and H. P. Becker Angew.Chem. Internat. Edn. 1967,6 876. C. Eaborn R. A. Jackson and R. Pearce Chem. Comm. 1967,920; C. Eaborn R. A. Jackson ad R. W. Walsingham J. Chem. Soc.(C) 1967 2188. C. Eaborn W. A. Dutton F. Glockling and K. A. Hooton J. Organometallic Chem. 1967,9 175. la3 H. M. J. C. Creemers and J. G. Noltes J. Organometallic Chem. 1967,7 237. E. Amberger and R.W. Salazar G. J. Organometallic Chem. 1967,8 11 1. H. Schumann T. Ostermann and M. Schmidt J. Organometallic Chem. 1967,8 105. N. S. Vyazankin M. N. Bochkarev and L. P. Samina J. Gen. Chem. (U.S.S.R.) 1966,36 1169. N. S. Vyazankin R. V. Mitrofanova and 0.A. Kruglaya J. Gen. Chem. (U.S.S.R.) 1966 36 166.