12 Organometallic Chemistry Part (ii) Main-Group Elements By J. L. WARDELL Department of Chemistry University of Aberdeen Meston Walk Old Aberdeen AB9 2UE 1 Introduction Reviews on various aspects of organometallic chemistry were published in 1981. Amongst these were the following (i) the formation of Grignard reagents from chemically activated magnesium,' (ii) uses of silicon compounds in organic syn- thesis, (iii) organotin compounds in ~ynthesis,~ (iv) photochemistry of organopoly- ~ilanes,~ (v) organic compounds of divalent tin and lead,5 and (vi) calculations of electronic structures of main-group organometallics.6 Two volumes on organo- antimony(1Ir) compounds have appeared in the Gmelin series.' 2 General One significant growth area in recent years has been cross-coupling reactions of in particular magnesium zinc aluminium mercury and tin compounds.These reactions most frequently catalysed by nickel or platinum complexes were abun- dantly reported in 1981. The synthesis of allyl-arenes from either PhCH2ZnBr and vinylic halides or vinylic alanes and PhCH2X (see Scheme l),described by Negishi et al. can be added to the established reactions which lead to aryl-benzyl alkenyl-allyl and aryl-ally1 coupled compounds.8 From another study,g the reactivity of allyl-X in couplings to alkenyl- and aryl-metals (metal = A1 or Zn) was found to decrease in the sequence X = halogen OAc > OAlR > OPO(OR) > OSiR3. The regioselectivity in catalysed reactions of (E)-RCH=CHCH2X or H,C=CHCHRX (R = Me or Pr; X = C1 OH or OR) with Grignard reagents apparently depends on the metal catalyst used." Scheme 2 shows examples of the effect of the catalyst.Y. H. Lai Synthesis 1981 585. * I. Fleming Chem. SOC.Rev. 1981,10 83. M. Pereyre and J. P. Quintard Pure Appl. Chem. 1981 53 2401. M. Ishikawa gnd M. Kumada Adv. Organomet. Chem. 1981,19 51. J. W. Connolly and C. Hoff,Adv. Organomet. Chem. 1981,19,123. D. R. Armstrong and P. E. Perkins Coord. Chem. Rev. 1981,38 139. 'M. Wieber Organoantimony Compounds Parts I and 11 Gmelin Handbook of Inorganic Chemistry Springer-Verlag Berlin 1981. E. I. Negishi H. Matsushita and N. Okukado Tetrahedron Lett. 1981 22 2715. E. I. Negishi S. Chatterjee and H. Matsushita Tetrahedron Left. 1981 22 3737. lo T. Hayashi M.Konishi K. I. Yokota and M. Kumada J. Chem. Soc. Chem. Commun. 1981 313. 281 282 J. L. Wardell Scheme 1 Me OSiEt PhMgBr 4yPh + pPh + Me-Ph -Catalyst ’ (1) Me (4) Me or (3) (5) Compound Catalyst Proportion (3):(4) :(5) (1) “iClz(dppf)l 88 :11:1 (1) [PdCl2(dPPf)l 4:92:4 (2) “iCb(dppf)l 81 :10:9 (2) [PdCl* (dPPf)l 9:75:16 (dppf = 1,1‘-bisdiphenylphosphinoferrocene) Scheme 2 Predominant inversion of configuration occurs“ in the reaction of (+)-(S)-but-l-en-3-01 and PhMgC1. Use of NiC12 complexes of chiral phosphines e.g. (S)-Pr’CH(NMe2)CH2PPh2 and (-)-norphos in coupling reactions of vinyl bromide to racemic alkyl-Grignard reagents,I2 e.g. PhMeCH(CH2),MgX (n = 1 or 2) and norborn-2-ylmagnesium halides leads to some asymmetric induction e.g.reac-tion (1). NiCl ‘PPh,’ H2C=CHBr + MeCHPhMgX + H2C=CHCHPhMe (1) 9’5”/0chemical yield [67% optical yield of (S)-isomer] A general cross-coupling reaction has been established with organomercurials. A wide range of alkyl- alkenyl- and aryl-mercurials readily react with primary and secondary alkyl- and alkenyl-cup rate^,'^ e.g. reaction (2). H. Felkin M. Joly-Goudket and S. G. Davies Tetrahedron Lett. 1981 22 1157. l2 T. Hayashi K. Kanehira T. Hioki and M. Kumada Tetrahedron Lett. 1981,22,137; H. Brunner and M. Probster J. Organornet. Chem. 1981 209 C1. I3 R. C. Larock and D. R. Leach Tefrahedron Lett. 1981,22,3435. Organometallic Chemistry -Part (ii) Main-Group Elements The biaryl cross-coupling of 1-methyl-2-pyrrolyl-MgBr (or -ZnBr) with aryl halides catalysed by [PdC12(Ph2PCH2CH2CH2CH2PPh2)]{ = [PdCl2(dppb)]} has also been rep~rted,'~ and is shown in Scheme 3.Me Me Me [87%] [73Yo] Reagents i (M = MgBr) PhBr THF heat for 1h [PdCl,(dppb)]; ii (M = ZnCl) QB THF heat for 1 h [PdCl,(dppb)] Scheme 3 Organotin compounds RSnMe3 (R = alkyl aryl indenyl or fluorenyl) react with ArX (Ar = Ph or nitrophenyl) at 120-130°C in the presence of Pd compounds in ClCH2CH2Cl solution to give good yields of RAr." Other interesting cross- coupling reactions16 produce p y-ethylene esters from vinylic halides and Refor- matsky reagents [reaction (3)] and allenic derivatives [reaction (4)]. RCH=CHBr + BrZnCH2C02Et HMPT'rPd(PPh3)41b RCH=CHCH,CO,Et (3) ,, Bt 45 .,c H2C=C=CHX or HCEC-CH~Y RZnBr*THF P H2C=C=CHR (4) [Pd(PPh&I [>80Yo] (X= Br or I Y = Br or Ac) (R = Ar vin 1, alkynyl or algnyl) An interesting aryl-coupling reaction of ArMgBr takes place in Et20 in the presence of ClCH,C=CCH,Cl (or ClCH,CH=CHCH,Cl); high yields (>70%)of Ar are obtained for meta-or para-(but not ortho-) substituted Ar gro~ps.'~ There have been several on the formation and detection of organometallic radical complexes [(R,ML)'] e.g.[RMg(phen)] [RMg(bipy)] [EtZn(Bu'NCHCHNBu')] [R2Al(bipy)] [R,M(thioketone)] (M = Si Ge or Sn) l4 A. Minato K. Tamao T. Hayashi K. Suzuki and M. Kumada Tetrahedron Left. 1981 22 5319. Is A. N. Kashin I. G. Bumagina N. A. Bumagin and I. P. Beletskaya J. Org.Chem. USSR (Engl. TrunsL),1981 17 18. K. Ruitenberg H. Kleijn C. J. Elsevier J. Meijer and P. Vermeer Tetrahedron Left. 1981 22 1451; J. F. Fauvarque and A. Jutand J. Orgunornet. Chem. 1981,209,109. l7 S. K. Taylor S.G. Bennett K. J. Heinz and L. K. Lashley J. Org. Chem. 1981 46 2194. E. C. Ashby and A. B. Goel J. Orgunomef. Chem. 1981,221 C15. l9 J. T. B. H. Jastrzebski J. M. Klerks G. van Koten and K. Vrieze J. Orgunornet. Chem. 1981 210 c49. *' W. Kaim J. Orgunornet. Chem. 1981 222 C17; A. Alberti P. F. Colonna M. Guerra B. F. Bonini G. Mazzanti Z. Dinya and G. F. Pedulli ibid. 1981 221 47; A. Alberti A. Hudson A. Maccioni G. Podda and G. F. Pedulli J. Chem. Soc. Perkin Trans. 2 1981 1274. 284 J. L. Wardell Rn+lM + L + [(RnML)'] and [R2M(benzo[2,1-b ; 3,4-b']dithiophen-4,5-dione)](M = As,'Sb or Bi).These complexes were prepared by the reaction of the appropriate organometallic com- pound with the chelating ligand L. In addition to these radical cation complexes of aluminium were also obtained21 [reaction (5)]. AlMez A new theoretical approach to nucleophilic addition to carbonyl groups has been put forward.** This involves charge-transfer stabilization of transition states. The feature of the transition state critical for stereoselectivity of the reaction is the existence of a low-lying vacant orbital UT associated with the u-bond that is being formed in the reaction. Electron delocalization into the u$ orbital will stabilize the transition state and may thereby enhance the reaction rate.The stereochemistry of nucleophilic addition to cyclohexanones is determined by two factors (i) steric hindrance which favours equatorial approach and (ii) electron donation from the ucc and uCH bonds of cyclohexanone into the ur orbital which favours the axial approach since the carbon-hydrogen bonds are better donors of electrons. 3 Group1 The use of ultrasound in organic synthesis has been further illustrated by the formation of R-R from equimolar amounts of lithium (in the form of a wire) and RX (R = aryl benzyl acyl or alkyl) in THF solution.23n This report comple- ments an earlier finding23b that good yields of RLi are obtained from lithium (4 equivalents) and RBr (e.g. R = Pr Bu or Ph) using ordinary ultrasound laboratory cleaners.7-Lithionorbornadiene has been prepared for the first time from 7-chloronorbornadiene and (p-Bu'C6H4C6H4Bu'-p)' Li' (6). The restated the advantages of using (6) (rather than sodium naphthalene) as the metallating agent as being that electron transfer is favoured over radical combination owing to the greater steric hindrance in (6) and that lithium as a counter-ion results in a lower degree of carbanionic character in the radical anion. &Substituted organo-sodium and -potassium compounds have been obtainedz5 by mercury-alkali-metal exchange reactions of organomercurial compounds [reac- tion (6)]. A study ab initio was conducted on the relative energies of R- and RLi. A close relationship (attentuation factor = 0.71) was found between the relative energies '' W.Kaim J. Organomet. Chem. 1981,215,325,337. *' A.S.Cieplak J. Am. Chem. SOC.,1981 103,4540. 23 B. Han and P. Boudjouk Tetrahedron Lett. 1981 22 2757; J. L.Luche and J. C. Damiano J. Am. Chem. SOC.,1980,102,7926. 24 J. Stapersma and G. W. Klumpp Tetrahedron 1981 37 187. " J. Barluenga F. J. Fananas and M. Yus,J. Org. Chem. 1981,46,1281. Organometallic Chemistry -Part (ii)Main-Group Elements 285 (i) PhM R-CH-CH2HgBr (ii) M b R-CH-CH2M’ (6) I I ZH ZM (R = H or Ph; Z = 0 or PhN; M = Li Na or K; M’ = Na or K) of the carbanion (R-) and those of the corresponding lithium compounds RLi (R = alkyl alkynyl cycloalkyl or cycloalkenyl).26 It thus appears quite reasonable to equate the carbanion with the corresponding organometallic compound.von R. Schleyer and co-workers have also continued their theoretical studies on the structures of organolithium compounds and have reported on further non-classical structures e.g. of LiCH2X (X = OH or NH2) [the structures of lowest energy i.e. (7) contain bridging HO or NH2 groups] LiCH2CH2Li (partially bridged structure) and (2,6-x2C6H3Li) (8; X = H or OH). The structure for (8)that has X H.. / \ ‘C-Li (7) X = OHorNH2 the lowest energy calculated by the MNDO method contains planar tetraco- ordinate bridging carbon Extended aromatic n-delocalization the stability of multi-centre cr-bonds involving lithium and intramolecular solvation were con- sidered to be responsible for this arrangement. MNDO calculations on the dimeric disolvate (PhLi.H20)2 however pointed to tetrahedral bridging carbon atoms in the most stable structure.The change from planar to tetrahedral bridging carbon atoms is a consequence of lithium becoming a poorer 0-donor and n-acceptor on intermolecular complexation. It is interesting that the closest species to (PhLi.H20)2 to have its structure determined by X-ray crystallography28 was (P~L~sTMED)~ which does contain tetrahedral bridging carbons. The X-ray structure of (2,6-MeOC6H3Li)6.Li20 (9)has been ~btained.~’ Perhaps because of the presence of the Li20 moiety the structure of (9) is far removed from that predicted by von R. Schleyer et al. for [2,6-(H0)2C6H3Li]2. In (9) there is a Li80 cluster which is composed of two Li pyramids each of which is connected to the oxygen via its Li base.The remaining six Li faces are occupied by aryl groups. There is considerable interest in polylithiated species. While it is possible to prepare CLi4 CH2Li2 etc. it has been difficult to characterize them owing to poor solubility thermal instability [e.g.see reactions (7)and (S)] and lack of appreciable vapour pressure up to 650°C. However it now appears that polylithiated species may survive for short distances on flash vacuum thermolysis; e.g. 90% CH2Li2 successfully negotiated a distance of lOcm under vacuum on being heated from 26 P. von R. Schleyer J. Chandrasekhar A. J. Kos T.Clark and G. W. Spitznagel J. Chem. SOC., Chem. Commun. 1981,882. 27 J. Chandrasekhar and P. von R. Schleyer J. Chem. SOC. Chem.Commun. 1981 260; A. J. Kos E. D. Jemmis P. von R. Schleyer R. Gleiter U. Fischbach and J. A. Pople J. Am. Chem. Sac. 1981 103,4996; T. Clark P. von R. Schleyer K. N. Houk,and N. G. Rondan J. Chem. SOC.,Chem. Commun. 1981,579. 28 D. Thoennes and E. Weiss Chem. Ber. 1978,111,3157. 29 H. Dietrich and D. Rewicki J. Orgunornet. Chem. 1981 205 281. 286 J. L. Wardell CL~~ B CLL + ~2~i4 + ~ yi; + ~3~i4 2 ~ i ~ (7) [20°/0] [3OYo] [40°/o J [lOYo] CL~~ :iLi + C2Li2 [100 Yo ] room temperature to 1500 "C in less than 3 seconds. The ion (CH2Li2),,+ (n = 1-5) was detected.,' Lithiation of terminal mono- or di-alkenes has been achieved" by using lithium in the presence of 1,5-diphenyl-l,6,aA 4-trithiapentalene (10) and ZnC12 or FeCl,; e.g.reactions (9) and (10). In contrast RCH=CH2 is lithiated by lithium in the presence of (10)and PdCl to give allyl-lithiums. s-s-s P h w Ph RCH=CH2 + Li (10) b (E)-RCH=CHLi (9) ZnCI or FeCI Several chiral ligands have been used in asymmetric addition of RLi to carbonyl the chelating compound (1 1) proved particularly effective resulting in 95% e.e. in the reaction of BuLi with PhCHO in Et20 at -120 "C. (11) New syntheses of aldehydes33 and ketones34 have been reported [reactions (11) and (12)]. 4 Group2 A new procedure for the preparation of highly reactive zinc or magnesium metal powders involves reduction of the metal chlorides in glyme by lithium with a 30 L. A. Shimp J. A. Morrison J. A. Gurak J. W. Chinn Jr. and R. J. Lagow J. Am.Chem. SOC. 1981,103,5951. " B. Bogdanovic and B. Wermeckes Angew. Chem. Int. Ed. Engl. 1981,20,684. 32 J. K. Whitesell and B. R. Jaw J. Org. Chem. 1981 46 2798; J. P. Mazaleyrat and D. J. Cram J. Am. Chem. SOC.,1981,103,4585. 33 G. A. Olah and M. Arvanaghi. Angew. Chem. Int. Ed. Engl. 1981 20,878. 34 S. Nahm and S. M. Weinreb Tetrahedron Lett. 1981,22 3815. 287 Organometallic Chemistry -Part (ii)Main-Group Elements (i) RLi or RMgX + RCHO+ Q (ii) H,O+ CHO H [e.g. R = Ph; 94%] 0IIR'C-N MeOMe (i) R2Li or R2MgX R' 'c=o (ii) H,O+ R2' [R' = Ph R2 = Me; 93%] catalytic amount of naphthalene present as an electron carrier. The zinc powder so formed is particularly reactive more so than that obtained from reduction with it reacts with PhBr (to give a 73% yield after refluxing for one hour) and C1CH2C02Et.Magnesium slurries obtained by evaporation of Mg in a rotating- solution reactor reacted with cyclopropylmethyl bromide in THF and with benzo- cyclobutenylmethyl bromide at low temperatures to give high yields of unre-arranged Grignard reagents as shown by trapping with COz or PhCHO. Normal methods of forming Grignard reagents provide very much more ring-opened prod- uct~,~~ e.g. as shown in Scheme 4. Polar aprotic sulphonamides in particular [Sole product] [Sole product] Reagents i Mg slurry Et20 at -50 "C; ii C02,H20; iii Mg (granulated) THF,at 30 "C Scheme 4 (Et2N)2S02 have been shown to be useful solvents for Grignard reaction~.~~ Solutions of RMgBr (R =Et Pr" Pr' or Ph) in (Et2N)2S02 prepared in high yields e.g.of 87% in Pr'MgC1 at ambient temperature are stable for weeks. Solutions in hexane (25%) of ZnEt and 2 equivalents of (Et2N)2S02are also stable. Whitesides3* has reported further on the mechanism of formation of a Grignard reagent. The forms of the dependence on the rate of reaction of cyclopentyl bromide with a rotating disk of magnesium in Et20 on the angular velocity and on other factors are all those that would be expected for mass-transfer-limited reactions. Additions of RMgX to alkynes catalysed by [(Cp),TiC12] selectively produce (E)-alkenyl Grignard reagents in almost quantitative yields,39 e.g. Scheme 5. Ashby has reported further4* on Grignard additions to carbonyl compounds. When a Grignard reagent reacts with a diary1 ketone Ar2C0 a radical anion- '' R.D. Rieke P. T. J. Li T. P. Burns and s.T. Uhm J. Org. Chem. 1981,46,4323. 36 E. P. Kundig and C. Perret Helu. Chim. Actu 1981,64 2606. 37 H. G. Richey Jr. R. D. Smith B. A. King T. C. Kester and E. P. Squiller J. Org. Chem. 1981 46 2823. 38 K. S. Root J. Deutch and G. M. Whitesides J. Am. Chem. SOC.,1981,103,5475. 39 F. Sato H. Ishikawa and M. Sato Tetrahedron Lett. 1981,22 85. 40 E. C. Ashby and J. R. Bowers J. Am. Chem. Soc. 1981,103,2242. 288 J. L. Wardell Ph PhCGCMe + Bu'MgBr A \ /Me Ph \ /Me /c=c\HBrMg + /c=c 'MgBr [90Yo ] [loo/,] ii 1 PhCMe=CMeH + PhCH=CMe2 90 10 Reagents i [(Cp),TiCl,] ii Me1 Scheme 5 radical cation pair is formed. This can collapse to the 1,2-addition product or dissociate to a radical anion and a free radical within the solvent cage.Further reactions can lead to the 1,2-addition product or a conjugate (e.g. 1,6-) addition product or the radicals can escape from the solvent cage to form pinacol. The 1,2-addition products show free-radical character as indicated by the cyclized addition product from the reaction of Ph2C0 with a tertiary Grignard reagent [e.g. H2C=CH(CH2)3CMe2MgCl in THF] or a primary Grignard reagent [e.g. H2C=CH(CHz)2CMe2CH2MgBr in Et20]. The 1,6-addition process also shows some free-radical character (Scheme 6). R RMgX + Ph2C=0 + Ph2C=O--Mg/ $ [Ph2C-0- RMgXt] (a-complex) \ "J 1 R' + PhzC-OMgX -[PhzC-OMgX R'] + PhzCOMgX I R 11 RH Ph2C-OMgX H -1 (1,2-adduct) etc.PhzCI -0MgX Roc:;Mgx (1,6-adduct) Scheme 6 Ashby4' has also obtained the first direct evidence for the involvement of the s.e.t. mechanism in reductions of Ar,C=O e.g. (mesityl),?C=O (see Scheme 7) using RMgX where R is a primary secondary or tertiary alkyl group. The rate of electron transfer [step (a) in Scheme 71 does not depend on the stability of R. radical and is in the sequence R = But > Pr' > Bus > Et > hexenyl > Bu' > PhCH = ButCH2> Me while the rates of transfer of P-hydrogen [step (b)] are in the order Et > hexenyl > Pr' > Bus > Bu' >> But. Combination of the two steps renders Bu"MgBr a useful reducing agent. The reaction of (CF&Hg and Me2Cd in donor solvents (L = THF glyme diglyme or py) pr wided (CF3)2Cd.L,.These complexes are generally more reactive than (CF,),Hg; e.g. products derived from a carbene ( CF2) can be obtained at lower temperature^.^^ '* E. C. Ashby and A. B. Goel J. Am. Chem. SOC.,1981,103,4983. 42 L.J. Krause and J. A. Morrison J. Am. Chem. SOC.,1981,103,2995. Organometallic Chemistry -Part (ii) Main-Group Elements X / (mesityl)2C=O + RMgX $ (me~ityl)~C=O--Mg a,[(mesityl)&-~ RMgXt] 'R (a-complex) (A,, ca. 575 nm) Scheme 7 The role of charge-transfer (C/T) complexes of mercury salts and arenes in mercuriation reactions has been investigated. Absorption maxima for the complexes Hg(OCOCF3)2.ArH in solution in CH2C12 are at 267(PhC1) 273(PhH) and 288 nm ArH + HgX2 + ArHgX (mesitylene) re~pectively.~~ The second-order rate constants for the disappearance of these C/T absorptions coincide with the rate-constants (k) for mercuriation of the arenes.The relative reactivities (log k/ko)of arenes in mercuriation are linearly related to the relative charge-transfer energies (Ahva) using PhH as the reference arene. Thus the transition state for mercuriation can be linked to the charge-transfer excited state [ArHt Hg(OCOCF3)27]$. Kochi and Fukuzumi have also considered oxymerc~riations.~~ A significant finding was that while there are quite distinct R'CH=CH2 + HgXz + R20H + R'CHOR2CH2HgX patterns of reactivities in brominations and oxymercuriations of alkenes the reac- tivities of the alkenes appear identical when the differences between the steric effects in the transition states for bromination and oxymercuriation are explicitly taken into account.Barluenga et al. have reported on amidomercuriation and sulphonamidomercuri- ati~n;~' these reactions were coupled with subsequent demercuriations (Scheme 8). R3CONHCHR'CHR2HgN03 3 R3CONHCR'CH2R2 R'CH=CHR~ TsNHCHR'CHR2HgN03 -% TsNHCHR'CH2R2 (Ts = p-MeC6H4S02) Reagents i Hg(NO,), CH,CI, reflux; ii R3CONH,; iii NaBH,; iv TsNH Scheme 8 Hydroxymercuriations of mono- or di-substituted alkenes occur in high yield and with very high regioselectivity (Markownikov) when HgX2 (X = OAc 43 S. Fukuzumi and J. K. Kochi J. Phys. Chem. 1981 85 648; J. Am. Chem. SOC.,1981 103 7240; J. Org. Chem. 1981,46,4117. 44 S. Fukuzumi and J.K. Kochi J. Am. Chem. SOC.,1981,103,2783. J. Barluenga C. Jimenez C. Najera and M. Yus J. Chem. SOC.,Chem. Commun. 1981,670 1178. 290 J. L. Wardell i ii RO Ro RO RO (R=PhCH;?) OH Reagents i Hg(OAc), THF at 20°C; ii aq. KCl; iii Et,BuN+ C1- OH- NaBH, CH,Cl,; iv 0,. NaBH, Me,NCHO Scheme 9 OCOCF3,NO3,or 03SMe) is used. In marked contrast only Hg(OAc) was effective in the Markownikov hydration of 1,1-di-,tri- and tetra-substituted alkene~.~~ Use of the oxymercuriation-demercuriation of alkenes has been made in a carbohy- drate4’ synthesis (e.g. Scheme 9). Reduction of organomercurials RHgX including oxymercuriated species to RH has been achieved using N-benzyl-1,4-dihydroni~otinamide.~~ In addition Bu3SnH has proved to be superior to NaBH4 in reductions of peroxymercurials prepared from non-terminal alkene~.~’ Giese et al.” have reported on further synthetic uses of radicals that were generated by the reduction of RHgX using borohydride reagents; a good illustration is the one-pot coupling of dienes and electron-deficient alkenes (Scheme 10).H2C=CHCH=CH2 H2C=CHCH(OMe)CH2HgOAc ii 1 iii iv H2C=CHCH(OMe)CH2CH2CYZH t-[H2C=CHCH(OMe)CH2.] Reagents i Hg(OAc), MeOH; ii NaBH(OMe),; iii H,C=CYZ (Y= H Me or C1; Z = CN COMe or C0,Me); iv hydrogen abstraction Scheme 10 5 Group3 The mechanism of the zirconium-catalysed carboalumination of alkynes has been further examined. These reactions are indeed direct carboaluminations assisted by zirconium-containing species (rather than carbozirconations assisted by an alane).’l The reaction of hept-1-yne and Et,Al in the presence of MeClZr(Cp) [reaction 46 H.C. Brown P. J. Geoghegan Jr. and J. T. Kurek J. Org. Chem. 1981,46,3810. 47 J. R. Pougny M. A. M. Nassr and P. Sinay J. Chem. SOC.,Chem. Commun. 1981 375. 48 H. Kurosawa H. Okada and T. Hattori Tetrahedron Lett. 1981 22 4495. 49 A. J. Bloodworth and J. L. ‘Courtneidge J. Chern. SOC.,Chem. Commun. 1981 1117. B. Giese and K. Heuck Chem. Ber. 1981 114 1572; B. Giese K. Heuck and U. Lunig Tetrahedron Lett. 1981 22 2155. ” T. Yoshida and E. I. Negishi J. Am. Chem. SOC., 1981,103,4985. Organometallic Chemistry -Part (ii)Main-Group Elements 291 n-C5H11 H (i) MeClZr(Cp) \c=c/ + n-C5HI1C=CH +Et3Al (ii) H,O Et' \H 70 L93% total yield J (13)] gave only traces of methylated alkenes.Rapid Me/Cl exchanges occur in the Me3A1/C12Zr(Cp) system but not in any other Me,A1C13-,/Me,C12-,Zr(Cp)2 mixtures; however all systems undergo carbometallation reactions of hept- 1-yne. Negishi also recommended51 that to limit the extent of hydroaluminations that occur when using branched-chain alkyl-alanes the combination R2A1Cl/Cl2Zr(Cp), rather than R,Al/Cl,Zr(Cp), should be employed. Carbo- aluminations of propargyl or homopropargyl derivatives5 that contain OH OSiMe2Bu' SPh or I by Me3Al proceed in a highly stereo- and regio-selective manner to give the corresponding (E)-(2-methyl-alkeny1)dimethylalanes(12). This high regioselectivity is in marked contrast to other known carbometallations.Cleavage of the C-A1 bond in (12) can lead52 to a variety of difunctionally substituted alkenes (e.g. see Scheme 11). Z(CH&CrCH Z(CH2) H -%Z(CH2) H \/ \/ Me /C=C\AlMe2 Me/c=c \C02Me (12) (Z =OH OSiMe2Bu' SPh or I; n =1or 2) Reagents i Me,Al Cl,Zr(Cp), at r.t. ClCH,CH,Cl; ii ClC0,Me Scheme 11 The reactions of R3Al (R =Me Et or Bu) with diary1 ketones or Ph,CCl were shown to proceed via s.e.t. mechani~rns;~~ (mesityl),CH was obtained from (mesityl),CO and Et,Al in THF. Reactions of isobutylaluminium halides with Pr'COPh have been investigated in Et20 solution at 0 "C. Di-isobutylaluminium halides rapidly reduce the ketone to Pr'CHOHPh but BuiAlX2 and Bu3'A12X3 give rise to Pr'CHXPh and Me2C=CHPh in addition to the carbinol.When chiral (2-methylbuty1)aluminium derivatives are employed both Pr'CHOHPh and Pr'CHXPh are optically active.53 Addition reactions of various organo-aluminium compounds R21A1Y (Y =OR2 SR2 SeR' or NR22) have been reported; 1,4-addition of R2A1SPh or of R2AlSeMe to @-unsaturated carbonyl compounds occurs; the reaction of the aluminium enolates with aldehydes provides aldol add~cts;~~ e.g. see reaction (14). Aminolysis of epoxides occurs readily if Et2AlNR2is [reaction (15)]. The compound 4-Me-2,6-Bu2'C6H20A1Bu2' has been shown to be a most useful 52 C. L. Rand D. E. van Horn M. W. Moore and E. I. Negishi J. Org. Chem. 1981,46,4093. "G. Giacomelli and L. Lardicci J. Org. Chem. 1981,46 3116. 54 A. Itoh S. Ozawa K. Oshima and H.Nozaki Buff.Chem. Soc. Jpn. 1981,54 274. "L. E. Overman and F. A. Flippin Tetrahedron Lett. 1981 22 195. 292 J. L. Wardell reductant in prostaglandin syntheses e.g. for reducing PGE methyl ester to PGFz methyl ester in 95% chemical yield and with 100% selectivity.’6 The compound Me(CHz)3CH(OMe)CH2Tl(OAc)2, prepared from hex-l-ene and Tl(OAc) in MeOH is stable for a week. By contrast the methoxythalliation adduct obtained from Tl(OCOCF3)3 undergoes rapid oxidative dethalliation (ca. 85YO dethalliation after 1 hour) to give 1,Z-dimethoxyhexane and 2-metho~yhexanol.~~ The Me0 and HO groups in these products were considered to arise by easy exchange of ligands at the thallium centre followed by transfer of these Me0 or HO groups from thallium to C-1 in a SNiprocess.6 Group4 Further work has been carried out on silenes. Dimethylsilene (MezSi :) generated from Me12Si6 by photolysis adds regiospecifically to allylic methyl ethers and allylic methyl s~lphides;~~ e.g. see reaction (16). MelzSi6 -% MeZSi Me,C=CHCH,OMe b H2C=CHCMezSiMezOMe Insertion of (Me,Si)PhSi :[produced from (Me3Si)3SiPh] into a variety of carbon- chlorine bonds of RCI has been reported” (R = allyl alkyl or vinyl; e.g. see Scheme 12). (Me3Si)3SiPh -% (Me3Si)PhSi (Me3Si)PhSi + R2C=CHX RzC-CHX + [ >/ ]Ph hMe3 RzC=CH X \//St+ Ph SiMe3 X = C1,R = H X = Br,R = Me Scheme 12 56 S. Iguchi H. Nakai M. Hayashi H. Yamamoto and K. Maruoka. Bull. Chem. SOC.Jpn. 1981,54,3033. ’’ A.J. Bloodworth and D. J.Lapham J. Chem. SOC.,Perkin Trans. I 1981,3265. ’* A.Chini and W. P. Weber Inorg. Chem. 1981,20 2822;D.Tzeng and W. P. Weber J. Org. Chem. 1981 46,693. ’’ M. Ishikawa K. I. Nakagawa and M. Kumada J. Organomet. Chem. 1981 214 277; M.Ishikawa K. 1. Nakagawa S. Katayama and M. Kurnada ibid. 1981 216 C48;J. Am. Chem. Soc. 1981,103 4170. Organometallic Chemistry -Part (ii)Main-Group Elements 293 The spirosilane (13) has been produced by the reaction of butadiene6' with the cyclic silene (14) (Scheme 13). The spirosilane was also obtained from the con- densation of silicon vapour with butadiene in a Timms 'freeze-fry' metal- evaporation apparatus (a temperature of ca. 1600 "C was required).60 (310°C) . H2C=CHCH=CH2, Si I / Meo'3 GiD Me& (14) (13) Scheme 13 Dimethylgermylene (MezGe :) generated61 from 7-germabenzonorbornadienes (15) added stereospecifically (as expected for a singlet species) to (E,E),4-diphenylbutadiene and to diallenes (Scheme 14).Only the (Z,Z)-and (E,E)-pairs Me Me \/ R A [Me2Ge:] -!!+ PhoPh Ph H /ce\'H ki R Me Me (15) /\ MC Me (16) R' = Me,R2 = Ph R' = Ph,R2 = Me Reagents i heat at 70-150 "C; ii (E,E)-PhCH=CHCH=CHPh; iii meso-PhMeC=C=C=C=C=CMePh Scheme 14 of isomers of (16) were obtained from meso-diallene. This is as anticipated for a thermal [2 + 41 cheletropic reaction of the Me2Ge The X-ray structures of (Cp),Sn and (MeSC=J2Pb have been determinedq6' Each compound is monomeric and has pentahapto-bonded rings; for (Cp),Sn d(Sn-C) is 2.56-2.85 A the angles (ring centroid)-Sn-(ring centroid) being 148.8 and 143.70'; for (Me,C,),Pb d(Pb-C) is 2.69-2.90 A and the angle (ring centroid)-Pb-(ring centroid) is 151".The divalent Pd" species (17) is monomeric and soluble in such as THF MezN-CH; (17) 60 P. P. Gaspar Y.S. Chen A. P. Helfer S. Konieczny E. C. L. Ma and S. H. Mo J. Am. Chem. Soc. 1981,103,7344. 61 M.Schriewer and W. P.Neumann Angew. Chem. Znt. Ed. Engl, 198120 1019. 62 J. L. Atwood W. E. Hunter A. H. Cowley R. A. Jones and C. A. Stewart J. Chem. SOC.,Chem. Commun. 1981,925. 63 P.P. de Wit H. 0.van der Kooi and J. Wolters J. Organomef. Chem. 1981 216 C9. 294 J.L.Wardell CHC13 or PhH [reaction (1 7)].Reversible thermal decomp~sition~~ of R3SnSnR3 to the radical R3Sn' occurs in compounds having bulky R groups; for (2,4,6-R3C6H2)3SnSn(2,4,6-R3C6H2)3, the dissociation temperatures are 180 100 and 20 "C for R =Me Et and Pr'.The silaethene (18) (m.pt 95 "C) was obtained by photolysis of the acyl-silane (19); compound (18) was characterized by i,r. n.m.r. and mass spectra.65 On standing in solution (18) reverts to (19). 0 II (Me3Si)3Si-C-C10HI5 (Me&)zSi=C ,OSiMe3 \ ClOHl5 (18) v(Si=C) = 1135 cm-' S[29Si(sp2)]=41.8 p.p.m. S['3C(spZ)] =214.2 p.p.m. 3 Silaethenes (21)have been synthesized by retro-diene cleavages of (20),under flash vacuum pyrolysis (Scheme 15) and trapped in argon matrices at 10 K. The i.r. and U.V. spectra of (21) were recorded.66 Six, /I (20) Y =CF3 or (X =H D or C1) COZMe Reagents i YCzCY; ii flash vacuum pyrolysis (650"C; lop4Torr) Scheme 15 Evidence was found for the isomerization of 2-silapropene (MeSiH=CH2) and dimethylsilylene (Me2Si :).Dimethylsilylene photolytically generated from Me12Si6 in an argon matrix at 10 K or a hydrocarbon matrix at 77 K is converted into MeSiH=CH by visible light.Annealing of argon matrices of MeSiH=CH2 at 50 K provides the dimer (Scheme 16); however at a higher temperature and in a hydrocarbon matrix rapid reversion to MezSi :OCCU~S.~'From the low-pressure pyrolysis of 1-methylsilacyclobutane at 625"C in a flow system both MeSiH=CH2 hr Me H (450nm) Ar matrix \n/ Me,Si:= MeSiH=CH Si Si EtCHMeEt /v\ matrix H Me at 100K Scheme 16 64 H.U. Buschhaus W. P. Neumann and T. Apoussidis Liebigs Ann. Chem. 1981 1190. 65 A. G. Brook F. Abdesaken B. Gutekunst G. Gutekunst and R. K. Kallury J. Chem. Soc. Chem. Commun. 1981,191. 66 G. Maier G. Mihtn and H. P. Reisenauer Angew. Chem. Znt. Ed. Engl.. 1981,20,597. 67 T. J. Drahnak J. Michl and R. West J. Am. Chem. Soc. 1981,103,1845;R. T.Conlin and D. L. Wood ibid. p. 1843. Organometallic Chemistry -Part (ii)Main-Group Elements and Mez% :could be separately trapped by butadiene and Me,SiH respectively in yields greater than 60%. Thermolysis and photolysis of (22) provide different products,68 as illustrated in Scheme 17. It was reported that photointerconversion of (22) and (23) occurs at Conditions i heat; ii hv Scheme 17 all temperatures studied.In solution loss of MezSi=SiMez and isomerization to (23) are competing decomposition pathways of (22). In argon or 3-methylpentane matrices loss of MezSi=SiMez from (22) is prevented and so only photoisomeriz- ation occurs. Trapping of MezSi=SiMe2 by anthracene or cyclopentadiene was also reported. Amongst the products of the flash vacuum pyrolysis of (24) is the dimer of 1-methylsilatoluene (25),69 which suggests the intermediacy of the silatoluene formed as shown in Scheme 18. Conditions i heat at 600 “C (1,3-rearrangement); ii elimination of Me,SiOMe Scheme 18 Three distinct routes to carbon-metal-bonded compounds from metal-metal compounds have been reported. These are reactions of (i) Me3SiSiMe3 and dihalogenonitrobenzenes in the presence’’ of [Pd(PPh,),] [reaction (18)] (ii) R,MM‘ and alkyl alkenyl or aryl halides” (M = Ge Sn or Pb; M’ = Li or Na) HMPT for 3 h Me3SiSiMe3+ 2,5-C12C6H3N02-2-NoZ-5-ClC6H3SiMe3 (18) (2 equiv.) [(Ph,P),PdI 68 Y.Nakadaira T.Otsuka and H. Sakurai Tetrahedron Letf. 1981 22 2417 2421; J. D. Rich T. J. Drahnak R. West and J. Michl J. Organomet. Chem. 1981 212 C1. 69 T. J. Barton and M. Vuper J. Am. Chem. SOC. 1981,103,6788. ’O H. Matsumoto K. Shono and Y.Nagai J. Organomet. Chem. 1981,208 145. ” M. S. Alnajjar and H. G. Kuivila J. Org. Chem. 1981 46 1053; J. san Filippo and J. Silbermann J. Am. Chem. SOC. 1981,103,5588; V.S. Zaugorodnii N. D. Grigor’eva and A. A. Petrov Zh. Obshch. Khim. 1981,51,2155; W.Kitching H. Onszowy and K.Harvey J. Org. Chem. 1981,46,2423. 296 J. L. Wardell and (iii) alkyne~~~ and cuprates e.g. (PhMezSi)zCuLior (R3SnCuX)Li which provide alkenyl-metal compounds. Organosilylated hydroxylamines R:Si -N(OR2)X (X = Et02C ArCO ArS02 or Me) have been shown to be nitrene [reaction (19)]. The OR2 RtSiN ’ -B R$iOR2 + [ :N-X] (19) ‘x stereochemistry of nucleophilic substitutions at chiral germanium centres e.g. (25) has been extensively studied. The stereochemical results are similar to those found for silicon O-Me Ge / ‘*.\ X Me (25) X = C1 OR SR NRz or PR2 7 Group5 Arsabenzene (26) undergoes electrophilic substitutions mainly at the 2-and 4- positions; e.g. the ratio of rates of acetylation at -78 “C are 40 :(1):300 for the 2- 3- and 4-positions respectively.Arsabenzene is lo3-lo4 times more reactive than PhH. Other substitutions that have been studied by Ashe were nitration and proton-deuteron exchange as well as protodesilylation of 2-and 4-trimethylsilyl- ar~abenzenes;~~ in the proton-deuteron exchanges and protodesilylations the 2-positions were more reactive than the 4-positions which is the opposite of the finding for acetylation and nitration. Several interesting heterocyclic arsenic species have been synthesized; these included some fourteen-membered quadridentate cyclic ligands (27) prepared by high-dilution [reaction (20)]. The stereochemistry was assigned from the n.m.r. spectra. (20) (X = AsMeorPPh) Y = 0,L = OMes Y = S L = OMes Y = AsMe L = C1 72 E.Piers J. M. Chong and H. E. Morton Tetrahedron Lett. 1981 22,4905; I. Fleming T. W. Newton and F. Roessler J. Chem. SOC.,Perkin Trans. 1 1981 2527; D. E. Seitz and S. H. Lee Tetrahedron Lett. 1981 22,4909. 73 Y. H. Chang F. T. Chiu and G. Zon J. Org. Chem. 1981,46,342. 74 J. Dubac J. Cavezzan A. Laporterie and P. Mazerolles J. Organomet. Chem. 1981,209 25. ” A. J. Ashe 111 W. T. Chan T. W. Smith and K. M. Taba J. Org. Chem. 1981,46 881. 76 E. P. Kyba and S. S. P. Chou J. Org. Chem. 1981,46,860. Organometallic Chemistry -Part (ii)Main-Group Elements The first monocyclic three-membered arsenic ring compound (Bu'As) (28) has been obtained from the reaction of KBu'AsAsBu'K and Bu'AsC12 at -78°C. Compound (28) is table'^ in the dark and in the absence of air at -3O"C but it oligomerizes to (Bu'As) at room temperature.Another interesting cyclic arsenic derivative77 is But6Ass (29) which is the major product of the reaction between Bu'AsCl, AsC13 and Mg. Bu' Bu' Bu'As -AsBu' 'A! Bu'As AsBu' Bu' 'As' \A! Bu' Bu' 2,2',5,5'-Tetramethyldistibolyl (30) is a thermochromic compound. In reflected light (30) is iridescent purple-blue while in transmitted light it is bright red. In CSbLi CSb-SFJ Me Me Me (30) solution in CC1 or PhMe and in the melt it is pale- The crystal structure has some interesting features. The molecule adopts a staggered trans configuration about the Sb-Sb axis with the rings in approximately parallel planes perpendicular to this axis. All the Sb atoms are aligned in collinear chains along the b crystal axis; the Sb * -Sb intermolecular distance of 3.625(2) 8 should be compared with a van der Waals separation of 4.4 8,.The C-Sb-C bond angles are ca.90" indicating that p-orbitals of Sb are used in bonding. ". KN(SiM(,Iz n-C,H,,CHO + Ph&CH,CH,,BF THF n-c,H~,gc'J~ (21) 10% HMPT Me [loo% trans] Reactions of unstabilized arsonium ylides prepared in situ with aldehydes79 provide epoxides; e.g. reaction (21). Some routes to Ph2R'AsCH2R2 BF, which are used in these reactions are given in Scheme 19. Ph3As 5Ph3kH2Prn BF4-Ph3AsMe,BF4-Ph2AsLi -%Ph2AsCH2Pri " ii + Ph2Bu'&CH2Pri,BF4-Reagents i BuOH (CF,SO,),O py; ii Na'BF,-; iii PrI KN(SiMe,),; iv Pr'CHJ THF; v Bu'CI AICI Scheme 19 77 M.Baudler and P. Bachmann Angew. Chem. Int. Ed. Engf. 1981,20 123; M. Baudler J. Hellmann P. Bachmann K. F. Tebbe R. Frohlich and M. Feher ibid. p. 406. 78 A. J. Ashe 111 W. Butler and T. R. Diephouse J. Am. Chern. Soc. 1981,103 207. 79 W. C. Still and V. J. Novack J. Am. Chem. SOC.,1981,103 1283. 298 J. L. Wardell 0 0 0 iii 1 Reagents i Ph,BiCO (92%); ii PhSBi (72%); iii Ph,BiOCOCF (58%) Scheme 20 Further uses of phenylbismuth(v) compounds'' in organic synthesis have been reported. The compound Ph4BiOCOCF3 is a useful reagent for selective formation of phenyl-oxygen bonds. Comparisons with other phenylbismuth species are shown in Scheme 20. D. H. R. Barton J. C. Blazejewski B. Charpiot and W. B. Motherwell J. Chern.Soc.Chem. Commun. 1981 503; D. H. R. Barton J. P. Kitchen D. J. Lester W. B. Motherwell and M. T. B. Papoula Tetrahedron 1981.37 Suppl. No. 9 p. 73.