12 Organometallic Chemistry Part (ii) Main-Group Elements By J. L. WARDELL Department of Chemistry University of Aberdeen Meston Walk Old Aberdeen A59 2UE 1 Introduction An authoritative review of the synthetic uses of a-metallated isocyanides has appeared.' A comprehensive survey of the preparation of aryl- and heteroaryl- trimethylsilanes was made topics covered the direct C-Si coupling cycloaddition modification of silyl-aromatics by incorporation of further functional groups and conversion of existing substituents.2" Another useful review on organosilanes was concerned with electrophilic substitution.26 Among the points covered in a review on the stereochemistry of organo-arsenic compounds were configurational stability and the energy barriers to inversion of asymmetric amine~.~ Several methods of direct synthesis were also reported with direct electrochemical synthesis being re~iewed.~ This method has been successfully used for Cd Zn Hg Al In and Sn derivatives.The low-temperature co-deposition of metal vapours with solvents in high excess followed by warming and subsequent partial re-clustering of metal atoms allows preparations of very active metal atoms in the form of slurries to be made; organometallic derivatives of Cd Zn Al In Sn and Pb were readily obtained from these slurries and organic halides.' Another synthesis is the co- condensation of reactive free radicals [e.g.CH3* and CF3-; produced from C2H6 and C2FG by radio-frequency glow discharge] with metals at -196 "C; derivatives of Cd Hg Bi Ge and Sn were so prepared.6 2 Group1 Ab initiu M.O.calculations (STO-3G) were made on pentaco-ordinate cations CH3M2'(M = Li and Na as well as BeH and MgH). The structures (l),of symmetry C, can be envisaged as models for electrophilic substitutions occurring with reten- tion while the D3hstructure (2) is a model for processes that occur with inversion. The DJh form was calculated to be the more stable for CH3Li2+ a species that is U. Schollkopf Pure Appl. Chem. 1979,51 1347. (a) D. Habich and F. Effenberger Synthesis 1979,841;(6) T. H. Chan and I. Fleming ibid. p. 761. F. D. Yambushev and V. I. Savin Russ. Chem. Rev. 1979,48,582. D. G. Tuck PureAppl. Chem. 1979,51,2005. K. J. Klabunde and T. 0.Murd0ck.J. Org. Chem.1979,44,3901. T. J. Juhlke R. W. Braun T. R. Bierschenk and R. J. Lagow J. Amer. Chem. Soc. 1979,101,3229. 272 J. L. Wardell known in the gas phase. The results suggest (i) that three-centre two-electron bonds may favour linear over cyclic arrangements and (ii) electrophilic aliphatic substitu- tion may proceed either with retention or inversion of configuration depending on the circ~mstances.~" It was also pointed out that a second-row substituent e.g. M =Na stabilizes methyl cations CHzM' more effectively than does its first-row counterpart .7 H M-C-MI+ H H-..I MC+' H' 'M (2) D3h The stabilizing influence of Li substituents on strained or unsaturated molecules such as ethylene cyclopropane acetylene and various bi- and poly-cyclic species was calculated (STO-3G basis sets) to be significant; e.g.the strain in tetra- lithiotetrahedrane (3) was calculated to be less than one-fourth of that in tetra- hedrane itself.' The compound Li& (3) reported last year9 to be produced by photolysis of Li2C2 reacts with Me1 to give a species having all the properties expected of tetramethyltetrahedrane." von Schleyer" also looked at the structures energies and bonding of lithium-substituted allenes propynes and cyclopropenes by ab initio methods. The most stable arrangements involve acetylidic and bridging lithium atoms; e.g. allenyl-lithium has a bent carbon skeleton which accommodates simultaneous bonding of Li to C-1 and to C-3 as shown in (4) but not to the nearest atom C-2; for C,Li4 (5) H there are two such bridging lithium atoms and two acetylide-type lithium atoms.The carbenoid CHF,Li is suggested (from ab initio calculations) to exist in three isomeric forms (i) a CHF2- Li' ion-pair (ii) a CHFLi' F-ion-pair (6) and (iii) (the least stable) a CHF.LiF complex; i.e. none has a classical structure that contains tetra- hedral carbon." The 13C n.m.r. spectra of carbenoids (7) CBr3Li and MeCBr,Li all labelled with 13C at the carbenoid centre were recorded at -100°C in THF solution. From the CBr3Li spectrum three compounds could be dete~ted;'~ these ' (a) E. D. Jemmis J. Chandrasekhar and P. von R. Schleyer J. Amer. Chem. SOC.,1979 101 527; (6) T. Clark and P. von. R. Schleyer Tetrahedron Letters 1979,4641. J. D. Dill A.Greenberg and J. F. Liebman J. Amer. Chem. SOC.,1979,101,6814. M. G. Hutchins Ann. Reports (B),1978 75 120. lo N. S. Zefirov V. N. Kirin N. M. Yur'eva A. S. Koz'min N. S. Kulikov and Yu. N. Luzikov Tetrahedron Letters 1979 1925. E. D. Jemmis J. Chandrasekhar and P. von R. Schleyer J. Amer. Chem. SOC.,1979,101,2848. T. Clark and P. von R. Schleyer Tetrahedron Letters 1979,4963. l3 D. Seebach H. Siegel K. Mullen and K. Hiltbrunner Angew. Chem. Internat. Edn. 1979 18 784; H. Siegel K. Hiltbrunner and D. Seebach ibid. p. 785. Organ om eta llic Chemistry-Pa rt (ii ) Main -Group Elements Br Br-.. I Br.. ,C-Li ,CLLi,Br- Br Br Br (7) n=4or6 (8) (9) were the carbene :CBr2 and two CBr,Li species one having tetrahedral carbon and the other (more stable) either like (8) or (9),i.e.analogous to (6). All carbenoids exhibit large downfield shifts of the carbenoid carbons. Previously a preparation of primary alkyl-lithiums from olefins (Scheme 1)was reported; now a complement to it -the preparation of secondary or tertiary alkyl-lithium from the same olefins (Scheme 2) -has been p~b1ished.l~ R'R2C=CH2 + PhSH i,R'R2CHCH2SPh R'R2CHCH2Li Reagents i Radical initiator; ii Li THF Scheme 1 R'R~C=CH~+ PhSH 4R'R2C(SPh)CH2 R'R2CL,CH2 Reagents i HCIO,; ii Li THF Scheme 2 The relative ortho-directing ability of groups Y in aromatic lithiations has been further studied," both intramolecularly using YC6H4CONEt2 (1O) and inter- molecularly involving competition between phenyloxazoline and PhY for BuLi.After suitable trapping the metallation of (10) by Bu"Li and tetramethylethyl- enediamine in THF at -100°C indicated CONEt2 to be superior to S02NEt2 oxazoline MeO Me2NCH2 C1 C02H and Me in directing lithiation to an ortho-position. In the intermolecular reactions a sequence of ortho-directing ability was established as Me2NS02 >CONEt >oxazoline>CH,NMe anion crossover was detected e.g. between the compound o-LiC6H4C=NCMe2CH2 and PhS02NMe2. d Metallation of the acetal (H-2) protons in 1,3-dioxolans,l,3-dioxans,and open- chain acetals is only possible if the proton can occupy an equatorial-like con- formation; i.e. a preferred equatorial deprotonation even in the case of a carbanion a to oxygen.16 A hydroxyl substituent activates cyclopropanes towards metallation by Pr'Li; the major product of reaction of cyclo-C3H5CHR(OH) after carboxyl- ation,17 was cis-1-RCH(0H)-2-HO2C-cyclo-C3H4 the other products being the trans-isomer and l-RCH(OH)-l-H02C-cyclo-C3~.Lithiation of (E)-R'SCH=CHCH2XR2 (11; X = 0 or S) by BuLi occurs18 at the sp3 carbon; in contrast lithiation of (11;R'=Ph XR2=NMe2) happens as shown in Scheme 3. l4 C. G. Screttas and M. Micha-Screttas J. Org. Chem. 1979,44713. l5 (a) P.Beak and R. A. Brown J. Org. Chem. 1979,44,4463; (b) A. I. Meyers and K. Lutomski ibid.,p. 4464. l6 A. I. Meyers A. L. Campbell A. G. Abatjoglou and E. L. Eliel Tetrahedron Letters 1979,4159. G.W.Klumpp M. Kool,M. Schakel R. F. Schmitz and C. Boutkan J. Amer. Chem. SOC.,1979,101 7065. '* J.J. Fitt and H. W. Gschwend J. Org. Chem. 1979,44303. '"n J. L. Wardell PhS H BuLi H/-CNMe __* Li ---NMe Scheme 3 R'CH~ CHR2R3 H \/ i ii \C=N H/C=N R1R4C/H \CHR2R3 Reagents i LiNPr',; ii R4X Scheme 4 The lithiation and alkylation (Scheme 4) of aliphatic aldimines has been shown to give a ratio of syn-to anti-products of 96:4. This is interpreted as representing a minimum value for the syn :anti ratio of the lithiated aldimine intermediates." The factor responsible for the preferential syn stabilization though not yet identified is determined to be >18 kJ mol-'. Complete regiochemical control2' pertains in the generation of alkenyl-lithiums from arenesulphonylhydrazones(e.g. Scheme 5). Me Me Li \C=N-NHS02Ar & \C=N -5 \c=c / H / /\ C5HllCH2 CSHIlC/H \NS02Ar Me C5H1I I I Ar =~,~,~-PI-'~C~H~ Li Li Reagents i Bu'Li at -78 "C,THF; ii 0 "C Scheme 5 Transmetallation of allyl-tin and -lead compounds by organolithiums continues to be a most useful source of unsymmetrically substituted allyl-lithiums; the utility of the method is enhanced by development of new allylic-tin species uia Wittig-style reactions.21 Another source of allyl-lithiums i.e.the conrotatory ring-opening of cyclopropyl-lithiums (e.g. see Scheme 6) has also attracted further attention. The ring-opening of (12; X =CN) to endu,endo-and exu,exo-(13) proceeds at a slower rate than the isomerization of the latter to the thermodynamically more stable isomer exo endo-(13). Percentages of equilibrium conformations and rotational barriers in X 'H H\ 4c.y / -C -C + exo,exo-(13) H Ph / \ Ph Li+ Ph (12) endo,endo-(13) X =H alkyl aryl or CN Scheme 6 l9 R.R. Fraser and J. Banville J.C.S. Chem. Comm. 1979 47. *O A.R.Chamberlin and F. T. Bond Synthesis 1979,44. 21 D.Seyferth and R. E. Mammarella J. Organometallic Chem. 1979 177 53; D.Seyferth and K. R. Wursthorn ibid. 1979,182,455;B. Mauze ibid. 1979 170,265. Organometallic Chemistry-Part (ii) Main-Group Elements these and other allyl-alkali-metal compounds were determined. The potential steric congestion in the endo,endo-isomers is not realized as the rings adopt a cyclophane- like conformation; in addition an expansion of the angles at sp2carbon atoms of ally1 occurs." The dynamic behaviour and structure of propyl-lithium enriched with I3C and 6Li was studied by n.m.r.spectroscopy. An advantage of using 6Li is that its quadrupole relaxation is too slow (unlike that of 7Li) to perturb the spectra. The hexamer undergoes fast intra-aggregate C-Li bond exchange to at least -80 "C and inter- aggregate exchange at higher temperatures. Evidence was also gained for different species at lower temperature^.^^ 3 Group2 Interestz4 in (cyclopentadienyl)zberylliumremains high. New electron-diff raction data at 120" were interpreted as being compatible with a C, symmetry and in particular with a slipped sandwich (or pentahapto trihapto) model e.g. (14) -a angle between C5H5 planes = -.4(3)" (14) structure similar to that obtained by X-ray diffraction in which d3was shown to be 1.2 A but not compatible with D5dsymmetry or [v-C5H5 a-C,H5] structures.The potential energy of the molecule was found not to alter much as d3changes between 0 and 1.2 A. Ab initio calculations with a double-5 basis were also carried out. Lower energies are obtained for the [?r-C5H5 a-C5H5] and D5dmodels in keeping with various earlier calculations but clearly in conflict with the electron-diffraction data. Ionization potentials obtained from the He (I) photoelectron spectrum were compared with the calculated orbital energies satisfactory agreement being found for the slipped sandwich structure. The Raman spectra of solid (at -100 and 25 "C) and liquid [(C5H=J2Be](at 65 "C)also suggested the presence of 'IT-bonded rings -one pentahapto and the other polyhapto.Allylic magnesium compounds and benzyne generated in situ undergo three competing reactions (a)nucleophilic addition (b) ('IT' + T') and (C) (7r4+'IT') cycloadditions (Scheme 7). With cyclohexyne only nucleophilic additions result.* While the addition of R'MgX (R1= alkyl or aryl) to [BrMgC_CCHR20MgBr] (Rz=H or Me) in the presence of Cu'X provides 22 G. Boche K. Buckl D. Martens D. R. Schneider and H. U. Wagner Chem. Ber. 1979 112 2961; G. Boche K. Buckl D. Martens and D. R. Schneider Tetrahedron Letters 1979,4967;T. B. Thompson and W. T. Ford J. Amer. Chem. Soc. 1979,101 5459. 23 G. Fraenkel A. M. Fraenkel M. J. Geckle and F. Schloss J. Amer. Chem. SOC.,1979,101,4745. 24 A. Almenningen A.Haaland and J. Lusztyk J. Organometallic Chem. 1979,170,271; R. Gleiter M. C. Bohm A. Haaland R. Johansen and J. Lusztyk ibid. p. 285; J. Lusztyk and K. B. Starowieyski ibid. p. 293. 25 J. G. Duboudin B. Jousseaume and M. Pinet-Vallier J. Organometallic Chem. 1979,172 1. 276 J. L. Wardell Scheme 7 [(BrMg),C=CR1CHR20MgBr] allylmagnesiurn bromide26 produces the cyclized material (15). The carbomagnesiation of the unsaturated alcohols. Ph2(HO)C(CH2),CH=CHz (16; n = 0 1 2 or 4) and of cycloalkenols e.g. (2-cyclohexenyl)diphenylcarbinol(17) occurs using RMgX (R = alkyl PhCHz or But) and [(allyl)2Mg] but not with primary alkyl- or aryl-magnesium~.~~ The reaction is catalysed by Ni but is retarded in THF or if amines are present. The order of reactivity ofcompounds (16) was established as n = 1> 0 >> 2 >> 4.The mechanism of the uncatalysed reaction of (17) with [(CH2=CHCH2)MgX] is shown in Scheme 8,in OH OMgCH2CH=CH2 / Ph'Cb4 & Ph,,cI^ / -Ph,C /&CH ,CH=CH Reagents i CH,=CH2MgX. Scheme 8 which a unirnolecular cisaddition (with respect to the OH group) occurs.z7 The Grignard reagent (1 8) from MeCHCICHzCHMeCH=CHz cyclizes reversibly in ethereal solutions to stereoisomers of (19); at 100 "C,in THF the equilibrium constant K(= [(19)]/[(18)]) is 3.4 with a forward rate constant of 6.8 x s; these values comparez8 with those for the unsubstituted cyclobutylmethylmagnesiurn & &CH2MgCl BrMgb CHR20MgBr Me MgCl Me (15) (18) (19) 26 J.G. Duboudin and B. Jousseaume Synth. Comm. 1979,9,53. " J. J. Eisch and J. H. Merkley,J. Amer. Chem. SOC.,1979,101 1148; J. J. Eisch J. H. Merkley and J. E. Galle J. Org. Chem. 1979,44,587. E.A.Hill and M. M. Myers J. Organometallic Chem. 1979,173 1. Organ ome tallic Chemistry -Part (ii) Ma in -Group Elements 277 system of 0.94 x and 2 x s. Compounds R1MgOR2 (20) as well as the zinc and aluminium analogues decompose on heating to an alkane R'H an olefin R2H and the metal oxide,29 in a process involving a cyclic six-centred transition state; e.g. methylmagnesium-threo- 1,2-diphenyl-1 -propoxide produces exclusively (2)-diphenylpropene. As (20) is produced from R12Mg and an alcohol the process is in essence a useful method of dehydrating alcohols.29 OMgX R'MgX + R'R'CHCO Scheme 9 The reactivity of R'MgX in the enolization of ketones e.g.as shown in Scheme 9 was established as R' = Et >Pr' >Me >> But and is a consequence of both steric and electronic factors. The reaction involved co-ordination of R'MgX to the ketone and subsequent rate-determining removal of hydrogen from the a-carbon in a six-membered transition Results from a detailed study of the reaction of PhCH2MgCl with H2C0 indicate that it is not the paradox as often stated but has many features in common with other aldehyde-benzyl-Grignard reactions; the products in yields that are dependent on the condition^,^' are o-Me2C6H4CH20H 0-HOCH2CH2C6H4CH20H,and PhCH2CH20H. Several T-arene complexes of cadmium@) and zinc(@ i.e.[M2+(ArH)] have been isolated from solutions of [Cd(AsF,),] [Cd(SbF6),] and [Zn(SbF6),] with methylbenzenes in liquid SO2. Related species [Hg2+(ArH),] (n = 1or 2) have also been prepared. Such complexes are sensitive to water and organic solvents. Stability constants for the complexes [Cd(AsF&.ArH] are smaller than those of [Hg2(ArH)]" and [Hg(ArH)]" and are in the range 0.5-2.1 1 mol-'. Localized bonding of the arene to the metal is indicated from 'H and 13C n.m.r. data; complexation generally produces deshielding of the '13Cd resonance.32 The first well-characterized organo-mercury(1) derivatives (21) have been described33 (Scheme 10). The corresponding Hg" ketenides (22) are similarly AcOHg-Hg H+ \ 2Hg2X2 + Ac20 3 /c=c=o XHg-Hg (21) AcOHg H+ \ 2HgX2+Ac20 -/ c=c=o X = OAc NO3 or C104 Scheme 10 29 E.C. Ashby G. F. Willard and A. B. Goel J. Org. Chem. 1979 44 1221. 30 A. G. Pinkus and W. C. Servoss J.C.S. Perkin ZZ 1979 1600. 31 R. A. Benkeser W. DeTalvo and D. Darling J. Org. Chem. 1979,44 225. 32 L. C. Damude and P. A. W. Dean J. Organometallic Chem. 1979,168,123; 1979,181 1. 33 E. T. Blues D. Bryce-Smith and H. Karimpour J.C.S. Chem. Comm. 1979 1043. 278 J. L. Wardell prepared (Scheme 10). Complexes (21) and (22) [i.r. v(CC0) ca. 2070(s) v(HgC) 276(m) and v (CCO) 62O(w)] are probably polymeric being involatile infusible and insoluble species and (happily) non-explosive except for X = C104. Reactions with dilute hydrochloric acid [providing Hg"' (n = 1 or 2) from (22) or (21)] with hydrogen chloride gas [producing keten and AcCl] and with bromine {giving [(XHg,)(AcOHg,)CBrCOBr];X = c104,n = 1 or 2 from (22) or (21)} as well as thermolysis (to C20) all support the proposed formulae.The secondary deuterium isotope effects in the intramolecularly competing methoxymercuriation of CH2=CD2 (23) (Scheme 11)and cis-MeCH=CDMe were CH2=CD2 -+ [MeOCH2CD2HgC1] + [MeOCD2CH2HgCl] (23) CY P Reagents i [Hg(OAc),] MeOH; ii NaCl Scheme 11 determined from the isomer ratios a :p to be 1.12 and 1.06 respectively. These values indicate that the transition states do not have symmetrical structures as do mercurinium ions but have appreciable C-0 bonding.34 4-Alkyl-cyclohexenes undergo oxymercuriation-demercuriation in a remarkedly stereoselective but non- regioselective manner; for 3-alkyl-cyclohexanes both a stereo- and regio-selectivity results.35 Organomercury complexes of guanosine (24) (GLH,; R = NH2) and related species including inosine (24; R = H) were amongst those Infrared (24) R = ribosyl spectra of solids prepared from MeHgNO or PhHgOH (R'HgX) at an appropriate pH as well as n.m.r.spectra in (CD,),SO solutions indicated that the binding sites were at N-1 for [RIHg(LH)] at N-7 for [R1Hg(LH2)]N03 and at both N-1 and N-7 for [(R'Hg)2(LH)]N03. In addition to these 1 1and 2 1species a 3 1complex i.e. [(MeHg),L]N03 (binding at N-1 N-7 and C-8) can be obtained either on heatingor on prolonged standing of solutions at pH 7 containing ratios of MeHgNO to LH2 of 3 1.The hydrogen attached to C-8has enhanced acidity owing to the co-ordination of MeHg at the adjacent N-7. The following conclusions were obtained from a study of the reduction of organo-mercury(I1) compounds by sodium dithionite (i) for simple alkyls the predominant reaction is a one-electron reduction to give an alkyl radical with the loss of any enantiomeric resolution possessed by prochiral substrates (ii) for aryl substrates symmetrization results and (iii) for oxymercurials reversion to an alkene 34 S. Shinoda M. Isemura and Y. Saito Bull. Chem. SOC.Japan 1979 52 1855. 35 H. C. Brown G. J. Lynch W. J. Hammar and L. C. Liu J. Org. Chem. 1979,44 1910. 36 E. Buncel A. R. Norris W. J. Racz and S. E. Taylor J.C.S. Chem. Comm. 1979,562; A.J. Canty and R. S. Tobias Inorg. Chem. 1979,18 413. Orga nom eta 11ic Chemistry -Part (ii) Main -Group Elements occurs.37 The reaction of oxymercurials with H2C=CHR (R = CN CO,Et or Ph) in the presence of [NaBH(OMe)J leads38 to the replacement of HgX by CHzCH2R (Scheme 12). + H2C=CHR + [NaBH(OMe),] -Scheme 12 4 Group3 A theoretical study using double-l basis sets was made on the complex between an aluminium atom and acetylene whose e.s.r. spectrum had previously been obtained at liquid-helium temperatures and interpreted as arising from a CT-bound complex. However the most stable of the bound isomers was calculated to be the vinylidene structure (25) (binding energy ca. 20 kcal mol-') while the cis-(and trans-)- AlCH=CH species (26) had a binding energy of only ca.8 kcal mol-'. A resolution of this apparent conflict was suggested3' to be that at the temperature of liquid helium there is insufficient energy to overcome the barrier of the 1,2-hydrogen shift required for conversion of (26) into (25). Matrix-isolation techniques were used to obtain the complex between an aluminium atom and benzene.40 It was deduced that A1 complexes with one of the C=C units of the ring. H A1'\c=c. AI-C=CH~ \H (25) (26) Hydroalumination of alkynes by [HA1(NR2)J in the presence of [Cp2TiC12] as catalyst in benzene occurs stereospecifically with cis- addition; e.g. from PhC=CMe,(E)-[PhCH=CMeA1(NR2),] (10%)and (E)-[(R2N),A1(Ph)C=CHMe] (90%) were obtained. The regiochemistry of the product(s) is determined by that of the intermediate alkynyl-titanium Carbometallation of certain alkynols can be accomplished under mild conditions with transition-metal-organo-aluminiumsystems; e.g.[Et2AlCl] [Cp2TiC12] and HC=CCH2CH20H at 0 "C provides after hydrolysis trans-EtCH=CHCH2CH20H and CHz=CEtCH2CH20H in a 1:1ratio. Changing the catalyst to the more bulky and less readily reduced [(q5-MeC6H4)2TiC12] increases the overall yields but without having much effect on the regio~electivity.~~ Organo-zirconium(1v) complexes have been as precursors of organo- aluminiums (Scheme 13). The transmetallations occur more readily for alkenyl than 37 L. M. Sayre and F. R. Jensen,J. Org. Chem. 1979,48 228. 38 B. Giese and K. Heuck Chem. Ber. 1979,112,3759,3766.39 M. Trenary M. E. Casida B. R. Brooks and H. F. Schaefer J. Amer. Chem. SOC.,1979,101 1638. 40 P. H. Kasai and D. McLeod J. Amer. Chem. Soc. 1979,101 5860. 41 E. C. Ashby and S. R. Noding J. Organometallic Chem. 1979,177,117;see also J. Org. Chem. 1979,44 4364. 42 D. C. Brown S. A. Nicholas A. B. Gilpin and D. W. Thompson J. Org. Chem. 1979,44 3457. 43 D. B. Carr and J. Schwartz J. Amer. Chem. Soc. 1979,101 3521. 280 J. L. Wardell c1 [CpzZr(H)ClI__* CpzZr' -% [CpzZrClz]+ (RAICl2) 'R Reagents i alkene or alkyne; ii AlCl Scheme 13 alkyl substituents and proceed predominantly with retention of configuration at carbon. Acyl groups can also be transferrred. Silica-supported titanium chloride and polystyrene-supported titanocene dichloride have been to catalyse the hydroalumination of alkanes and dienes by LiA1H4.Racemic l-olefins are iso- merized by the homogeneous catalytic system (R)-NN-dimethyl- l-phenyl- ethylamine-A1Bu'3-nickel(N-methylsalicylideneamine)z:both the unchanged 1-olefins and the (E)-2-olefins that are formed are optically active indicating that the reaction is stereoselective; e.g. EtCPhHCHzCH=CHz is 35% isomerized to (-)-(R)- (E)-EtCPhHCH=CHCH3 (0.24% optical purity) with the unchanged l-olefin having a (+)-(S)config~ration~~ (0.12% optical purity). Cyclopropylmethyl allylic and benzylic acetates are alkylated by trialkyl-aluminiums in CHzCl2 solution at room temperature; carbo-cationic intermediates have been detected.46 Esters may be converted into amides by treatment with R'zA1NR2z; thus m-N02C6H4C02Me and [EtzA1NH2] from [Et,Al] and NH3 produced rn-NozC6H4CONH2 in 91'/o yield.47 Thallium(II1) tris(trifluoromethylsu1phonate)is much more effective in aromatic thallati~ns~~ than is [Tl(OCOCF,),]; mono-thallation of polyfluoro-benzenes readily occurs using [Tl(OSO,CF,),] in CF3CO2H.Oxythallation of norbornene deriva- tives using [Tl(OAc),] in MeOH provides cis-exo-acetoxythallated adducts (27),in contrast to the analogous reaction of the mercury compound which leads to the methoxy-derivatives. Treatment of the adducts (27) with NaBH4 provides olefins and some exo-al~ohols.~~ 5 Group4 The preparation and spectroscopic characterization of the elusive species dimethyl- silylene MezSi (28) has been achieved.Irradiation at 254 nm of (MezSi)6 in rigid hydrocarbon glasses at 77K produces singlet silylene (28) (Y= 1220cm-' A, =453 nm). Trapping of (28) by various agents including hexene but not MezSi(OMe)* was possible. Irradiation of (28)with visible light led to the formation of 2-silapr0pene.~' As well as the usual traps for silylenes e.g. P-diketones and alkene~,~' a silylene such as (28) can be trapped as its dimer MezSi=SiMez by anth~acene;~~ thus heating 2,3-dibenzo-7,7-dimethyl-1,4,5,6-tetraphenyl-7-.UF. Sato H. Ishikawa Y. Takahashi M. Miura and M. Sato Tetrahedron Letters 1979 3745. 45 G. Giacomelli L. Lardicci R. Menicagli and L. Bertero J.C.S. Chem. Comm. 1979,633. 46 A. Itoh K. Oshima S. Sasaki H. Yamamoto T. Hiyama and H. Nozaki Tetrahedron Letters 1979,4751.47 J. L. Wood N. A. Khatri and S. M. Weinreb Tetrahedron Letters 1979,4907. 48 G. B. Deacon and D. Tunaley Austral. J. Chem. 1979,32,737. 49 S. Uemura H. Miyoshi M. Okano I. Morishima andT. Inubushi J. Organometallic Chem. 1979,165,9. T. J. Drahnak J. Michl and R. West J. Amer. Chem. SOC.,1979,101,5427. W. Ando and M. Ikeno J.C.S. Chem. Comm. 1979,655;M. Ishikawa K. I. Nakagawa and M. Kumada J. Organometallic Chem. 1979 178 105. 52 Y. Nakadaira T. Kobayashi T. Otsuka and H. Sakurai J. Amer. Chem. SOC. 1979,101,486. Organometallic Chemistry-Part (ii) Main-Group Elements 281 . D1 Si=Si, / Me Ph RR3 (29) R3 (301 silanorbornadienein the presence of anthracene at 350 "C provides (29; R' =R2= Me R3-R3 = -CH=CHCH=CH-).Geometric isomerism in Si=Si bonded species e.g. (30); has been Thermolysis of (29; R' = Me R2 = Ph R3 =H) in the presence of anthracene at 300°C provides (29; R'=Me R2=Ph R3-R3= -CH=CHCH=CH) via trans-(30). In a similar fashion the cis-isomer also reacts stereospecifically. The use of higher temperatures and less reactive enophiles than anthracene lead to a reduced stereoselectivity. These results clearly show the Si=Si to be a true double bond with slow (E)",(2)isomerism at the temperatures used. 53 During an ab initio study using non-empirical pseudopotential methods on various C2H4Si isomers it was calculateds4 that the stability sequence is silylacetylene<silacyclopropene (3 1)=silacyclopropylidene (32) <2-sila-allene < 2-silapropyne.Particularly noteworthy was the stability of singlet (32) and the non-aromatic character of (3 1).Photolysis of HC_CSiRl2SiRz3 provides silylethyl- enes silacyclopropene and silapropadiene derivatives (e.g.as in Scheme 14). These PhMeSi=CH2 + HC-CSiMe2Ph hu HCGCSiMezSiMezPh __* + 'She2 PhMe2SiCH=C=SiMe2 Scheme 14 Reagents i LiNPr', C5HI2 0 "C Scheme 15 were trapped" by MeOH. Successful attempts have been made56 to generate and trap the silylbenzene derivative (33). Compound (34) was generated from 1 l-di-n- butyl-4-t-butyl-4-methoxy-l,4-dihydrostannin. To contrast with Scheme 15 only substitution at silicon occurs when the less hindered (34; R =Me X = C1) is treated with LiNEt, to give initially (34; R=Me X=NEt,). Trapping of (33) by con- jugated dienes provides (7'+ 7') cyclo-adducts." H. Sakurai Y. Nakadaira and T. Kobayashi J. Amer. Chem. SOC.,1979,101,487. 54 J. C. Barthelat G. Trinquier and G. Bertrand J. Amer. Chem. Soc. 1979,101,3785. 55 M. Ishikawa H. Sugisawa K. Yamamoto and M. Kumada J. Organometallic Chem. 1979,179 377. 56 G. Mark1 and P. Hofmeister Angew. Chem. Internat. Edn. 1979 18 789. 282 J. L. Wardell Interest has been maintained in research on silaethylenes A direct experimental determination of AH for Me2Si=CH2 was made using ion cyclotron resonance The method employed was to determine the minimum base strength required for the formation and detection of BH' by ion cyclotron resonance via deprotonation of Me3Si' (Scheme 16) and then from the known B + Me3SiCI 5Me3Si+ 2Me2Si=CH2 + BH+ Scheme 16 enthalpy of proton transfer to the base B a value for AHf (ca.20.5 kcal mol-*) was obtained.A T-bond energy of 34 kcal mol-' was also calculated. Lower values were reported for these properties from calculations based on the thermodynamic cycle involving the thermal decomposition and dissociative ionization processes for 1,l-dimethyl-1-silacyclobutane.57b Photolysis of acyl-p~lysilanes~~ at 360 nm gives rise to carbenes and/or silaethyl- enes of enhanced stability (Schemes 17 and 18). While the trapping (by alcohols and OSiR R:SiSiR;C(0)R3 -% R:SiSiR&O-CR2 + RiSi=C / \R3 Scheme 17 0 (Me3Si)3Si-C-Bu'II hv ,0SiMe3 (Me3Si)2Si=C - (Me3Si)2Si-1 /OSiMe3C /\But \But (Me3Si)2Si- C-OSiMe3IBut Scheme 18 (35) unsaturated compounds) and dimerization of these silaethylenes were generally studied (Me3Si)2Si=C(OSiMe3)But was shown to have a moderate lifetime at ambient temperature and to be in equilibrium with its head-to-head dimer (35).Spectral characterizations were made by U.V. and by 'H I3C and 29Si n.m.r. The enhanced stability was attributed to both steric and electronic factors particularly of the Me3Si groups. The X-ray structure of (35) and another head-to-head dimer of a silylethylene i.e. (Me3Si)2C=C=SiPh2 were reported.59 Other silicon-carbon double-bonded intermediates were formed in the photolysis of 1-and 2-naphthyl- SiR2SiR3. From the 1-naphthyl derivatives,60 even in the presence of a trapping 57 (a) W. J. Pietro S.K. Pollack and W. J. Hehre J. Amer. Chem. Soc. 1979 101 7126; (b)L. E. Gusel'nikov and N. S. Nametkin J. Orgunometallic Chem. 1979 169 155. '13 A. G. Brook J. W. Harris J. Lemon and M. El-Sheikh J. Amer. Chem. SOC.,1979 101 83; A. G. Brook S. C. Nyburg W. F. Reynolds Y. C. Poon Y. M. Chang J. S. Lee and J. P. Picard ibid.,p. 6750. " M. Ishikawa T. Fuchikami M. Kumada T. Higuchi and S. Miyamoto J. Amer. Chem. SOC.,1979,101 1348. 60 M. Ishikawa M. Oda N. Miyoshi L. Fabry M. Kumada Y. Yamabe K. Akagi and K. Fukui J. Amer. Chem. SOC.,1979,101,4612. Organometallic Chemistry-Part (ii) Main-Group Elements 283 agent 1-HR2Si-2-R3Si-naphthaleneswere obtained uia 1,3-hydrogen shifts in the intermediate Si=C-bonded species. Claisen sigmatropic rearrangements of PhOSiMezCH=CHz (36) and related species were reported;61 (36) gave on heating at 350 "C l-oxa-5,6-benzo-2,2- dimethyl-2-silacyclohexane.Photolysis of Me3SiC( =N2)C02R1 in R20H yields products (i) Me3SiCHOR2C02R' from insertion of the corresponding carbene into the 0-H bond of R20H (ii) Me3SiC(OR3)HC02R2 (R3 = R' or R') by Wolff rearrangement and (iii) Me2Si0R2CMeCO2R' (37) apparently from the silene Me2Si=CMeC02R1. However in the gas phase,62 the precursor to (37) was shown to be the keten Me,Si(OR')C(Me)=C=O. A method of preparation of tri- substituted ethylenes stereoselectively is based on the reaction of R'COCR2HSiR33 with R4Li and on the subsequent highly discriminative elimination of R33Si and the oxide group from the adducts.syn-Elimination occurs under basic conditions whereas anti-elimination proceeds with Two preparations of that most useful reagent Me3SiI in situ have been published by Olah;64 these are the reactions of (Me& with I and of Me3SiCl with NaI in MeCN. The addition of Me3SiI to @-unsaturated ketones is a new use of this reagent.65 Gielen continued his work66 on chiral tin compounds with details of the synthesis optical stability and stereo-reactions of hydrides such as [(PhMe,CCH,)R(Ph)SnH] (R=Me or Bu'). The chiral hydrides obtained by asymmetric reduction of the corresponding racemic halides by chiral [HA1(OC6H3Me2-2,6)-(OCHPhCHMeNMe,)]- Li' only slowly racemize in benzene solution at room temperature (t+17days). The H-D exchange with [Ph3SnD] occurs with retention of configuration at tin.In contrast to the structure of [Ph3SnOSnPh3] those of O[(PhCH2)3M]2 (M = Ge or Sn) have linear M-0-M fragment^.^^ The synthesis and structure of the nido-cluster (38) was reported;68 compound (38) is sensitive to air and to moisture. As well as the fast intramolecular exchanges in [C5H5SnMe3] and [(cyclo-nonatetraenyl)SnMe,] (by 1,9-sigmatropic shifts) in solvents such as THF or DME [(MesCs)zSnll]+HBF4 Ph CN (39) 61 J. Ancelle G. Bertrand M. Joanny and P. Mazerolles Tetrahedron Letters 1979 3153. 62 W. Ando A. Sekiguchi T. Hagiwara T. Migata V. Chowdhry F. H. Westheimer S. L. Kammula M. Green and M. Jones J. Amer. Chem. SOC.,1979,101,6393. 63 M. Obayashi K. Utimoto and H. Nozaki Bull. Chem. SOC.Japan 1979,52 1760.64 G.A. 0lah.S. C. Narang B. G. B. Gupta andR. Malhotra J. Org. Chem. l979,44,1247;Angew. Chem. Internat. Edn. 1979,18 612. 65 R. D. Miller and D. R. McKean Tetrahedron Letters 1979 2305. M. Gielen and Y. Tondeur J. Organometallic Chem. 1979 169 265. 67 C. Glidewell and D. C. Liles J.C.S. Chem. Comm. 1979,93; Acta Cryst. 1979,35B 1689. 6a P. Jutzi F. Kohl and C. Kriiger Angew. Chem. Internat. Edn. 1979,18 59. 284 J. L. Wardell intermolecular exchanges via ion-pairs in the presence of HMPT have been recog- ni~ed.~' The 7-stannanorbornane derivative (39) from 1,l-dimethyl-2,3,4,5-tetraphenyl-stannacyclopentadieneand (CN),C=C(CN), is stable below -30 "C; at higher temperatures (39) decomposes (at -10 "C ti = 17 min) to 5,5,6,6-tetracyano- 1,2,3,4-tetraphenyl-1,3-cyclohexadieneand Me2Sn which can be trapped or allowed to p~lymerize.~' The insertion of (CN),C=C(CN) into C-Sn bonds proceeds uia charge-transfer complexes under both photochemical and thermal activation.The activation step is transfer of an electron from the charge-transfer complex the same paramagnetic and intermediate species being formed in both the thermal and photochemical reaction^.^' A similar study was concerned7* with the insertion of (CH)2C=C(CN)2 into H-M bonds (M = Si Ge or Sn). The sequence of events is given in Scheme 19 in which tcne is tetracyanoethylene (40) is a charge-transfer complex and ke,t.is the rate constant for electron transfer. R3MH + tcne -+ [HMR3-tcne] 5[HMR3' tcne'] (40) J [(CN)2HC(CN)2CMR3]e [H' MR; tcne'] Scheme 19 Palladium complexes in particular [PhCH2Pd(PPh3),C1] catalyse the coupling of %Sn with PhCH2X and ArX.Various functional groups are tolerated in this high-yielding synthesis. a-Deuteriobenzyl bromide and Me4Sn provide the inverted PhCHDMe Compounds [ArPb(OCOR),] prepared by plumbylation and by transmetallation of mercury and silicon derivatives are useful phenylating reagents towards ArH phenols and p-dike tone^.^^ 6 Group5 It has been variously established that correlations exist between core-ionization energies and proton affinities. The data for arsabenzene however fall well off the correlation line for arsines and it was considered that the low basicity is due to the inability to undergo the necessary geometric rearrangement on pr~tonation.~~ It was deduced76 from the n.m.r.spectrum of 4-methylstibabenzene in a nematic phase that there is no large C-C bond alternation within the ring and that the length of C-a-C-p is only slightly greater than that of C-p-C-7. The thermally labile 69 (a) G. Boche F. Heidenhain and B. Staudig Angew. Chem. Internat. Edn. 1979,18,218;(b)A. Bonny and S. R. Stobart J.C.S. Dalton 1979,786. 70 C. Grugel W. P. Neumann and M. Schriewer Angew. Chem. Internat. Edn. 1979,18 543. 71 S. Fukuzumi K. Mochida and J. K. Kochi J.Amer. Chem. SOC., 1979,101,5961;see also 0.A. Reutov V. 1. Rozenberg G. V. Gavrilova and V. A. Nikanorov J. Organometallic Chem. 1979,177,101. 72 R. J. Klinger K. Mochida and J. K. Kochi J Amer. Chem. SOC.,1979,101,6626.73 D. Milstein and J. K. Stille J. Amer. Chem. SOC., 1979,101 4992. " H. C. Bell J. R. Kalman J.T. Pinhey andS. Sternhel1,Austral. J.Chem. 1979,32,1521;H. C. Bell J. R. Kalman G. L. May J. T. May J. T. Pinhey and S. Sternhell ibid. p. 1531; H. C. Bell J. T. Pinhey and S. Sternhell ibid. p. 1551; J. T. Pinhey and B. A. Rowe ibid. p. 1561. 75 A. J. Ashe M. K. Bahl K. D. Bomben W. T. Chan J. K. Gimzewski P. G. Sitton and T. D. Thomas J. Amer. Chem. SOC.,1979,101 1764. 76 T. C. Wong M. G. Ferguson and A. J. Ashe J. Mol. Structure 1979 52 231. Organometallic Chemistry-Part (ii) Main-Group Elements arsanaphthalene (41) previously unknown was prepared77 as shown in Scheme 20. The 13C n.m.r. spectrum of (41) was obtained despite its slow decomposition in solution.Treatment of (41) with CF3C~CCF provides (42; R =CF3). R R (42)R= H (41) y4y Reagents i (R = 2-pyridyl) NdN R Scheme 20 Mesityl(diphenylmethylene)arsane [2,4,6-Me3C6HzAs=CPh2] which is a compound with an isolated double bond is stable at ambient temperature in the absence of air and shows little tendency to oxidize.” It was synthesized from [2,4,6-Me3C6HzAs(C1)CHPh2] and diazabicycloundecene. A. J. Ashe D. J. Bellville and H. S. Friedman J.C.S. Chem. Comm. 1979 880. 78 T. C. Klebach H. van Dongen and F. Bickelhaupt Angew. Chem. Internat. Edn. 1979,18 395.