12 Organometallic Chemistry Part (ii) Main-Group Elements By John D. KENNEDY Department of Inorganic and Structural Chemistry University of Leeds Leeds LS2 9JT 1 Introduction The two journals specializing in organometallic chemistry continue to thrive. Organornetallics is now well established and in this the Editor’s book reviews are recommended reading. Journal of Organornetallic Chemistry has reached its 250th volume and its 20th year and its Editor has been pleased to note an increase in the number of papers from groups in continental Europe. In both journals about 20% of the papers continue to be concerned principally with main-group chemistry. This is reasonable in terms of quantity but in general 1983 seems not to have been the greatest year in terms of the overall quality of organometallic main-group chemistry.Although there is fortunately lively activity in a variety of areas much of the other work this year has left this reporter with a feeling of dkjh uu. Too much of the chemistry seems very routine and in an increasing proportion of the genuinely innovative work the directing interest derives not from the organometallic chemistry itself but for example from the establishment of synthetic routes for organic chemists or from the chemistry of transition-metal centres which have main-group organometallic moieties as ligands. It is not clear whether this is a symptom or a cause of what appears to be a malaise in main-group chemistry in general. It is clear that main-group chemists in the U.S.A.feel that there are problems in maintaining the identity of and the momentum of work in the sub-discipline,’ and in the U.K. there has been dismay among main-group chemists at what they regard as disproportionately massive support for transition-metal chemistry. A large component of the solution to this problem either real or imaginary must rely on the continuous generation of innovative chemistry by the practising main-group chemists. Fortunately strong pockets of creativity are still present and as mentioned in last year’s report,2 a variety of areas ripe for expansion and/or exploitation can be readily identified. 2 Group I Covalent organometallic chemistry of the alkali metals other than lithium remains largely ill-defined and is generally limited to the observation of ‘short’ metal-to- carbon distances in compounds in which the metal is associated mainly with a more ’ A.H. Cowley Chem. Br. 1983 19 480.. ’J. D. Kennedy ARR.Rep. Prog. Chem. Secr. B 1982 79 257. 293 J. D. Kennedy electronegative element. In this context the short Na-C distance of 265.6 (1) pm has been reported this occurs in the trimeric species [(Me3SiNNa)2(SiMe2)]3 in which it is comparable with the longest Na-N bond of 260.1 (3) pm. Progress in organolithium chemistry has remained steady. The influence of ethereal solvents and also of lithium halides on organolithium reactivity is well recognized. Two pieces of work are of significance in this The structure of [(PhLiOEt2),LiBr] is based on a cubic-type framework as in structure (l) in which the atoms C are the ips0 carbons of the phenyl group^.^ The lithium atom opposite to the bromine is the one not co-ordinated to Et20.The distances to carbon from the ether-free lithium at 215 pm are some 13 pm shorter than from ether-bound lithium which may be related to the reactivity. Aryl-lithiums are generally held to be dimeric in solution. This work now suggests that tetrameric units may also be quite stable (unless particularly strong multidentate donors such as TMEDA are present) and indicates that further work on the solution structure of aryl-lithiums is warranted .4 The structure of the intramolecularly etherated tetrameric 3-lithio- 1 -methoxybutine (2; only one organyl group represented) is useful in view of the failure so far to obtain crystalline samples of straightforward alkyl-lithium-ether ad duct^.^ The dimensions are taken to suggest that bond lengths of tetrahedral organolithium clusters are not significantly affected by co-ordination of Lewis bases and that accelerations of reactions may therefore derive rather from strong effects on transition states by the ether additives.’ The compound [LiC(SiMe3)3(THF)2] a substance commonly used to attach the very bulky {C(SiMe,),} group has been shown to be [Li(THF)4][Li{C(SiMe3)3}2] the anionic lithiate unit having a linear C-Li-C system with Li-C (mean) 218 and Si-C (mean) 182 pm; it is the first lithiate species to be structurally character- ized.6 The bulky species [LiC(SiMe,Ph),(THF)] is uniquely monomeric (3).7 The metal atom is covalently bound to the THF oxygen and to the central carbon atom [212 (2) pm] of the {CSi,} unit and interacts strongly with the ips0 carbon atom of one of the phenyl groups [240 (2) pm].The aromatic hybridization at the ips0 carbon appears not to be significantly distorted (compare the aluminium species reported last year2). D. J. Brauer H. Burger W. Geschwandtner G. R. Liewald and C. Kriiger J. Organomet. Chem. 1983 2441. H. Hope and P. P. Power J. Am. Chem. SOC.,1983 105 5320. G. W. Klumpp P. J. A. Geurink A. L. Spek and A. J. M. Duisenberg 1.Chem. SOC.,Chem. Commun. 1983 814. C. Eaborn P. B. Hitchcock J. D. Smith and A. C. Sullivan J. Chem. SOC.Chem. Commun. 1983 827. ’ C. Eaborn P. B. Hitchcock J. D. Smith and A.C. Sullivan J. Chem. SOC.,Chem. Commun.. 1983 1390. Organometallic Chemistry -Part (ii) Main-Group Elements A series of metallocenes [(ba~e)LiC~H~(SiMe~)~] [e.g. (4)] has been characterized (base = quinuclidene TMEDA etc.).8These are air-sensitive crystalline solids and constitute the nearest approach yet to the simplest possible metallocene [Li(C,H,)]. The silylated lithiocenes have been used to prepare yellow crystalline polysilylated plumbocenes from PbC12.9 Other interesting organolithium work reported in 1983 includes the synthesis of optically active 2,2'-dilithio-6,6'-dimethylbiphenyl(5) prepared from the optically pure di-iodo-species and BuLi in Et20 solution." It is stable towards racemization at -10"C and has potential for the synthesis of optically active biphenyl series.Me Me \ 3 Group I1 Although organomagnesium compounds as Grignard reagents pervade the whole of chemistry the organic chemistry of the alkaline earths and of beryllium is not well represented. 1983 has been disappointing for organoberyllium chemistry but it has been interesting to see a report on the preparation and reactions of the solvent-free arylcalcium halides ArCaX." These are made by the reaction between ArX and calcium in the vapour phase and their reactions have been assessed under a variety of conditions that have been found useful for Grignard and organolithium reagents. In general however yields are lower than for these last two better- established reagent types. The organobarium compound [Ba(CMe2Ph)2] has also been reported,12 together with its use as a novel initiator in anionic polymerization.Over the past few years there has been an increasing incidence of the use of lithium organocuprates in organic synthesis and they are now reasonably well recognized as useful reagents. More recently the corresponding organomagnesium cuprates (Normant reagents) derived from the interaction of Grignard reagents with cuprous halides have attracted interest and have been used imaginatively in P. Jutzi E. Schluter C. Kriiger and S. Pohl Angew. Chem. Znt. Ed. Engl. 1983 22 994. P. Jutzi and E. Schluter J. Organomer. Chem. 1983 253 313. lo T. Frejd and T. Klingstedt J. Chem. Soc. Chem. Commun. 1983 1021. 'I K. Mochida and H. Ogawa J. Organomet. Chem. 1983 243 131.'' L.-C. Tang C. Mathis and B. Francois J. Organomet. Chem. 1983 243 359. J. D. Kennedy synthetic work (see other references cited in reference 13). Structurally these reagents have been generally represented as [RCuMgX,] [R2CuMgX] etc. but now solutions in THF have been found to contain species [CU~M~~M~,~+~] 1, where rn = n = 1-4 and 6 and where rn = 2 n = 3.13 Of these [CuMgMe,] is monomeric and [Cu2MgMe4] dimeric. The others are too unstable to be investigated but where n is large it is thought that the compounds are probably based on copper clusters. Another area more familiar in Group I chemistry is that of aromatic radical anions Ar’- and related benzenoid dianions A?-. This now has been more thoroughly examined for magnesium in THF solution and the deep blue anthracene radical anion and its yellow dianion have been characterized with {MgBr}+ co~nterions.’~ There seems to be the germ of a renaissance in organozinc chemistry although much of this is associated with the generation of transition-metal complexes.For example the mixed organozinc-tantalum species (6) is obtained by the use of [Zn(CH2CMe3)2] as a hydrogen-abstracting agent on [TaC13(CHCMe3) (MeOCH,CH20Me)].’S There may be a small but increasing underswell of the use of organozincs in synthesi~,’~”’ for example in P-unsaturated a-amino-ester forma- tion.” In organomercury chemistry steady work continues in the area of polymer- curiomethanes and related compounds u.v. i.r. and Raman spectra together with some preparative work have been reported for the mercuriomethanes them-selves.18-20 An interesting result is the crystal structure of the trimercurated acetal- dehyde species [(OHg,CCHO)( N0,)(H20)].2’ This compound is the product of the mercuration of acetaldehyde by aqueous mercury oxyacid salts and is also obtained from acetylene under similar conditions.The {Hg3CH=O} units are interconnected by oxonium oxygen atoms to form a polymeric columnar [OHg3CCH=O]:+ cation. The {Hg,O} oxonium pyramid is quite flat with the angles HgOHg averaging at 1 16°.21 4 Group I11 There have been few innovative developments in the organic chemistry of the Group I11 metals in 1983. The reaction in benzene solution between A1Me3 and sodium cacodylate Na[AsMe202] yields [A~Me,l~[Me~A10AlMe~]~.~~ This is of interest because firstly it demonstrates the complete methylation of the cacodylate anion l3 E.C. Ashby and A. B. Goel J. Org. Chem. 1983 48 2125 and references cited therein. 14 P. K. Freeman and L. L. Hutchinson J. Org. Chem. 1983 48 879. l5 A. W. Gal and H. van der Heijden J. Chem. SOC.,Chem. Commun. 1983 420. l6 G. A. Molander J. Org. Chem. 1983 48 5409 and references cited therein. 37 M. Bourhis J.-J. Bosc and R. Golse J. Organomet Chem. 1983 256 193. D. K. Breitinger and W. Kress J. Organornet. Chem. 1983 256 217. Iy D. K. Breitinger W. Kress R. Sendelbeck and K. Ishiwada J. Organomet. Chem. 1983 243 245. 20 J. Mink Z. MeiC M. Gil and B. Korpar-eolig J. Organornet. Chem. 1983 256 203. 21 D. Grdenit M. Sikirica D.Matovic&logoviE and A. Nagl J. Organornet. Chem. 1983 253 283. 22 J. L. Atwood and M. J. Zaworotko J. Chem. SOC.,Chem. Commun.. 1983 302. Organometallic Chemistry -Part (ii) Main-Group Elements 297 (one of the first organometallic species known) to the [AsMe4]+ cation and secondly there is the novel anion (7) to fit into the wide range of known aluminoxide structures. Another newly established organoaluminoxide anion is [A1706Me16]- which is encountered on the decomposition pathways of high-oxygen-content organoaluminium compounds such as K[A12Me602].23 Its structure is an open {A1606} cage capped by the seventh aluminium atom (8); each aluminium atom has two methyl groups bound to it and each oxygen one. Me o/A’,oP‘, A1 /\ A] ,A’rA ‘ /A Me,Al-0 ,0-AIMe 88 Al II Me* Al ,Al 0 (7) (8) A novel benzene sandwich complex of gallium [((C6H6)2Ga.GaC14}2( C6H6)3] may be crystallized from a solution of Ga,C14 in benzene under carefully controlled condition^.^^ It contains a quasi-tetrahedral gallium centre in a bent sandwich structure (9) the distances from the metal atom to the carbon plane averaging at ca.284 pm. Other new organogallium species include gallium(Ir1) porphyrins of general structure (10) ;these species are prepared by the reactions of LiR or RMgX on the appropriate chlorogallium( 111) p~rphyrin.~~ Gas-\? 5 Group IV As in last year’s report Group IV chemistry constitutes the bulk of 1983 published material in main-group organometallic chemistry and within this area organosilicon chemistry is predominant.There is a continuing general interest in the use of Group IV species as effective ligands in transition-metal chemistry and in processes such as the transition-metal catalysed reactions of silanes but the predominant interest in these fields is in directions other than the study of the Group IV organometallic chemistry itself. This also applies to the use of Group IV species as reagents for organic syntheses which is also a major field of research. The book ‘Silicon Reagents for Organic Synthesis’ was published in 1983. This seems to deal comprehensively 23 J. L. Atwood D. C. Hmcir R. D. Priester and R. D. Rogers Organornetallics 1983 2 985. ” H. Schmidbaur U. Thewalt and T. Zafiropoulos OrganornetaNics 1983 2 1550.25 A. Coutsolelos and R. Cuilard J. Organornet. Chern. 1983 253 273. 298 J. D. Kennedy with most aspects of the field implied by its title except for the silylation of OH SH and NH (which is reasonable) and it should be a useful information resource for the synthetic organic chemist.26 There are also more specific reviews on methods of preparaing siloxycyclopropanes and their use in organic ~ynthesis,,~ and on rhodium catalysts for enantiomeric hydrosilylation.28 Polymeric species other than silicones have attracted some attention. Alkylsilanes bound to silica gel are of interest because of the potential usefulness of their surface properties. Of this work to cite one example solid-state CP/MAS n.m.r. spectros- copy has been carried out on the product of the silylation of silica gel using dimethyloctadecylchlorosilane(DMODCS) in order to examine the surface struc- tural en~ironment.,~ Another polymeric species poly-( 1-trimethylsilyl)prop-1-yne prepared from the monomer using niobium and tantalum halide catalysts is of interest because of its exceptionally high permeability to 0 gas -an order of magnitude greater than that for [( Me,SiO),] for example.30 Disilene chemistry is now well established and 1983 has seen some consolidatory work in this area.New disilenes reported include tetra-ne~pentyl~' and tetra-t- b~tyl,~, and the structural type has now been characterized by a single-crystal X-ray diffraction analysis on the original tetramesityl deri~ative.~~ The Si=Si distance is 216.0 pm some 18-20 pm shorter than typical Si-Si single bonds the difference (in pm) being greater than that between C=C and C-C.In percentage terms the contraction is some 8-9% for disilicon and ca. 12% for dicarbon. By contrast ditin species such as [Sn,(N(SiMe,),},] exhibit intertin distances no shorter than those typical of intertin single bonds which is taken to indicate a significant T-bonding component for the intersilicon bond. There is however some pyramidaliz- ation at silicon with an angle of 162" rather than the planar 180°.33The 29Si nuclear shielding anisotropy in tetramesityldisilene [Mes2Si=SiMes2] is similar to that of 13C in ethylene whereas that in [Mes2HSi-SiHMes2] is similar to that of 13C in ethane also consistent with the conclusion that the electronic structures of the Si=Si and C=C double bonds are closely similar.34 Associated with this type of work some additional cyclotrisilanes [(SiR2)3] have been made.3',35*36 A tin analogue of these the cyclotristannane [(SnAr2)3] where Ar is {2,6-Et2C6H3} has also now been ~haracterized.~~ It is an orange crystalline compound m.p.(dec.) 175 "C obtained from the reaction between [Ar2SnC1,] and lithium naphthalene. The intertin distances average at ca. 286 pm and aromatic group rotation is slow on the n.m.r. time-scale. All that is now needed to complete the Group IV set is a cyclotriplumbane. 26 'Silicon Reagents for Organic Synthesis' W. P. Weber Springer Verlag 1983. 27 S. Murai I. Ryu and N.Sonoda J. Organornet. Cbem. 1983 250 121. 28 H. Briinner Angew. Chem. Int. Ed. Engl. 1983 22 897. 29 D. W. Sindorf and G. E. Maciel J. Am. Chem. SOC.,1983 105 1848. 30 T. Masuda E. Isobe T. Higashimura and K. Takada J. Am. Chem. Soc. 1983 105 7473. 3' H. Watanabe T. Okawa M. Kato and Y. Nagai J. Chem. Soc. Cbem. Commun. 1983 781. 32 S. Masamune S. Murakami and H. Tobita Organomeiallics 1982 2 1464. 33 M. J. Fink M. J. Michalczyk K. J. Haller R. West and J. Michl 1.Chern. SOC.,Cbem. Commun. 1983 1010. 34 K. W. Zilm D. M. Grant J. Michl M. J. Fink and R. West Organomeiallics 1983 2 193. 35 S. Masamune H. Tobita and S. Murakami J. Am. Chem. SOC.,1983 105 6524. 36 S. Masamune S. Murakami H. Tobita and D. J. Williams J. Am. Cbem. SOC.,1983 105 7776.37 S. Masamune L. R. Sita and D. J. Williams J. Am. Chem. SOC.,1983 105 630. Organometallic Chemistry -Part (ii) Main-Group Elements Other new silicon multiple-bond chemistry is the isolation of the second example of a stable silaethene [Me2Si=C(SiMe3)(SiMeBut2)] (1l) prepared by the 'thermal salt elimination' reaction of equation ( 1).38 It is a crystalline compound which decays within a few days at room temperature and probably lies at the limit of isolatability for these types of compound under normal conditions. Me SiMeBu' Me II /SiMeBu'2 Me-Si-C-SiMe d'Si=C (1) -LiF II F Li Me' 'SiMe (1 1) There is a certain fascination about trying to generate other stable multiply bonded silicon species. The true silicones {R,Si=O} are often postulated by inference trapping experiments et~.~~ but have not yet been detected directly.Corresponding species [Me,Ge=S] and [Me2Si=S] however formed in the thermolysis of [(Me2GeS)J and [(Me,SiS),] respectively have been detected by photoelectron spectroscopy.a Attempts to prepare silicenium ylides such as [R2Si= NBu'] have so far been unsuccessful although the work has generated some other interesting species such as [But&( NBu')C1AlCl2] (12).4' This however has a straightforward a-bonded framework. Ph\ SiMe An elegant piece of work has been the planned synthesis and characterization of the ethenyldisilacyclopropane species ( 13) an air-stable yellow crystalline com- pound m.p. 203°C.42 It was previously thought to be a disilacyclobutane.It is formed in 14% yield from the cophotolysis of [PhC=CSiMes,SiMeJ with [Me3SiSiMes2SiMe3]. Since photolysis of the first of these starting materials is presumed to yield Ph(Me3Si)C=C=SiMes2 and the second Mes,Si it was reasoned that their cophotolysis would yield the adduct of these two products as indeed it does. Much of this novel multiply bonded and smaller polysilane work utilizes bulky stabilizing groups on silicon. The use of such bulky groups on silicon or organosilicon moieties themselves as bulky groups forms the continuing basis of a lot of interesting chemistry in other areas but space considerations preclude the detailing of these this year. A review 'Steric Effects in Organosilicon Chemistry' may however be noted in this c0ntext.4~ N.Wiberg and G. Wagner Angew. Chem Znt. Ed. EngL 1983,22 1005. 39 G. Hussmann W.D. Wulff and T.J.Barton. J. Am. Chem Soc. 1983 105 1263. 40 C. Guimon G. Pfister-Guillouzo H. Lavayssiere. G. Dousse. J. Barrau qnd J. Satge J. Organomet. Chem 1983,249 C17. 41 W. Clegg U. Klingebiel J. Neernann and G. M. Sheldrick J. Organomer. Chem 1983,249,47. 42 M. Ishikawa H. Sugisawa M. Kumada T. Higuchi K. Matsui K. Hirotsu and J. Iyoda Organometallics 1983 2 174. 43 M. Weidenbruch and A. Schafer Rev. Silicon Germanium Tin Lead Comps. 1983 7 127. 300 J. D. Kennedy In larger polysilane chemistry a new class of polyfunctional silanes obtained from Bu,PCl-catalysed Si-Si/Si-Cl bond redistribution in methylchlorodisilanes has been reported.44 Products have polycyclic structures with about seven rings per molecule e.g.[( Me,Si),(MeSi) 17C15] ( 14) and alkylation arylation amination reduction and alcoholysis of the residual Si-Cl bonds have been examined. Other interesting classes of compounds synthesized in 1983 include a number of rotanes [(CH,),Si], such as (15p and some macrocyclic species based on combinations of polysilane units {(SiMe,),) and acetylene units {-C=C-} as ring components; of these last the species (16) is the smallest known cyclic diine.& Me Me I I \I Si Me The stability of the Si-0 bond remains the basis of a lot of chemistry much of which is routine. An interesting rearrangement is that afforded by the photolysis of trimethylsilylfuran [equation (2)] to give a formallenylsilane in high yield,"7 rather than a siloxane species which might otherwise be naively expected.The correspond- ing alkylfurans give complex mixtures of products in low yields under similar conditions. 0 I1 C H SiMe hu pentane -78 "C H/ \ c=c=c/ (2) 0 87% / \ H SiMe Readers will be excited to learn that it has been found that sila- and germa-tranones [for example as in (17)] can be readily made for example by straightforward transesterification reactions and so forth.48349 It is stated that in contrast to the widely studied metallatranes of the Group IV elements their carbonyl-containing derivatives have received only scant attention so fur (this reporter's italics). Does this presage a metallatranone mountain to rival the metallatrane one? A transesterification process has been used to synthesize the 'silacrowns' [R'R2Si( OCH,CH,),O] from polyethylene glycols and simple alkoxysilanes such as [R'R2Si(0Et),] mostly in yields of 50-80°h.50 This easy synthesis in principle enables the introduction of organic moieties that are without precedent in other crown ether systems.So far however the cation solubility enhancements found 44 R. H. Baney J. H. Gaul and T. K. Hilty Organometallics 1983. 2 859. 45 C. W. Carlson X.-H. Zhang and R. West Organometallics 1983 2 453. 46 H. Sakurai Y. Nakadaira A. Hosomi Y. Eriyama and C. Kabuto J. Am. Chem. Soc. 1983 105 3359. 47 T. J. Barton and G. Hussmann J. Am. Chem. SOC. 1983 105 6316. 48 E. KupEe E.Liepins A. Lapsina G. Zelchan and E. Lukevics J. Organomet. Chem. 1983 251 15. 49 G. I. Zelchan A. F. Lapsina and E. Lukevics Zh. Obshch. Khim. 1983 465. 50 B. Arkles K. King R. Anderson and W. Peterson Organometallics 1983 2 454. Organometallic Chemistry -Part ( ii) Main-Group Elements 301 Ph,Sn fiSnPh, I I R seem in general similar to those obtained by more conventional crown ethers. An interesting converse of the principle of Lewis-base crown ethers is afforded by the concept of Lewis-acid crown species as potential complexing agents for anions. This has led to the synthesis of the tin crown compound [Ph,Sn(CH,),] (18) via straightforward Grignard and lithium processes with the final cyclization performed under dilute condition^.^ No anion co-ordination of this twenty-membered ring species has been reported however.Electronegative substituents such as chlorine on tin would presumably enhance this type of behaviour. At the other extreme of cyclostanna-alkane chemistry is the four-membered {SnC,} ring of the first stannacyclobutane [Me2Sn(CH2)2CMe2]. This compound has been isolated in 5% yield as a colourless air-unstable liquid from the straightforward reaction between [Me,C( CH,MgBr),] and [Me2SiC12] at room temperature., A second novel four-membered ring is that in the tin( 11) species 1,3-dibutyl-2,2- dimethyl- 1,3,2,4h 2-diazasilastannetidine (19). This gives an adduct (20) with cyclo- pentadiene [equation (3)] but with cyclohexa- 1,3-diene an unexpected redox process occurs with a quantitative formation of C6H6 metallic tin and [Me,Sn( NHBu'),].~~ Other work noted in tin(I1) chemistry in 1983 is the exchange of the apical tin atom in the nido-cluster [SnC,Me,]+ as summarized in equation (4).54 Usually the apical tin in these species is attacked by nucleophiles.The process of equation (4) however is believed to occur via a more complex reaction sequence initiated by electrophilic attack on the cyclopentadienyl ring. In any event this M. Newcornb Y. Azurna and A. R. Courtney Organometallics 1983 2 175. 52 J. W. F. L. Seetz G. Schat 0.S. Akkerman and F. Bickelhaupt 1.Am Chem SOC.,1983 105 3336. 53 M. Veith and F. Tollner J. Organomet. Chem 1983 246 219. 54 F. Kohl and P. Jutzi Angew. Chem. Int. Ed. Engl, 1983 22 56.J. D. Kennedy novel type of reaction may provide a general access to a variety of other cyclopen- tadienyl element compounds with the nido-cluster structure.54 As usual there has been in 1983 a variety of synthetic and structural work in permutational chalcogenide chemistry of the Group IV elements. Much of this is now routine. In stannoxane chemistry two more [(R,SnO)3] ring systems have been reported in which the tin atoms are four-co-~rdinate.~~*~~ This low co-ordination number arises because the groups R are bulky [{2,6-EtzC6H3} and {(Me,Si),C}]. In related organogermanium chemistry hydrolysis of [Bu'GeCl,] yields [But2Ge( OH),] which is of straightforward four-co-ordinate tetrahedral geometry with inter- molecular H-bonding. Dehydration gives [(Bu',GeO),] which has a planar rather than a puckered {Ge303} ring.56 Hydrolysis of [Bu'GeC13] gives [(BUf2Ge)609] 'the first Group IV sesquichalcogenide [(RM),,Y,,] with n = 3'.This has two cyclic {Ge303} units joined by three Ge-0-Ge linkages (21).57 Other germanium work includes that involving the perfluorophenylgermanium unit {Ge(C,F,),}. In a truly main-group organometallic reaction involving mercury thallium germanium and lithium the treatment of [{ (C6F,)3Ge}3Hgfl( DME) .,] with lithium in dimethoxyethane (DME) is found to give what is believed to be the covalent species [{ (C6FS)3Ge}3HgLi( DME),] other metals generally produce ionic compounds of the [{ (C6F5)3Ge}3Hg]-M+ type.58 Some related work reports the synthesis of what may be Ge-TI bonded species uia the reaction of [(C6F5),GeH] with [TlEt,] [equation (5)].59 [(C,F,),GeH] + [TlEt,] -* [(C6F,),GenEt2] + CH,CH (5) There has been interest in the possibility that hydrogen atoms in positions antiperi- planar to Sn-C bonds may be an active source of hydrogen in redox processes.w2 This has led to the synthesis of inter alia the adamantane-like compound (22).This species has elements of strain not present in adamantane itself because the organic residue has to span the large {Sn3S3} ring and consequently the bridgehead carbon is apparently one of the most flattened methine groups known as well as being effectively antiperiplanar to three Sn-C bonds6 It is not yet clear however what general chemical effects this may have. 55 V.K. Belsky N. N. Zemlyanski I. V. Borisova N. D. Kolosova and I. P. Beletskaya 1. Organomet. Chem. 1983 254 189. " H. Puff S. Franken W. Schuh and W. Schwab J. Organomet. Chem. 1983,254 33. 57 H. Puff S. Franken and W. Schuh J. Organornet. Chem. 1983,256 23. 58 G. A. Razuvaev M. N. Bochkarev and L. V. Pankratov J. Organomet. Chem. 1983. 250 135. 59 M. N. Bochkarev T. A. Basalgina G.S. Kalinina and G.A. Razuvaev J. Organomet. Chem.. 1983,243 405. 60 A. L. Beauchamp S. Latour M. J. Olivier and J. D. Wuest J. Organomet. Chem 1983 254 283. 61 S. Chandrasekhar S. Latour J. D. Wuest and B. Zacharie J. Org. Chem 1983,48 3810. 62 A. L. Beauchamp S. Latour M. J. Olivier and J. D. Wuest J. Am. Cfiem. Soc. 1983 105 7778. Organometallic Chemistry -Part (ii) Main-Group Elements H I Organolead chemistry is not well represented in 1983.The linear relationship between the n.m.r. chemical shifts S('''Pb) and S( "'Sn) for equivalent straightfor- ward organolead and organotin species has been redisc~vered:~ and the synthesis of [Pb( SiMe3)J 'the first organosilicon-lead compound' has been reported.64 The preparation of this latter species [equation (6)] makes use of the silicon Grignard-type reagent [Mg( SiMe,),]. These reagents and corresponding aluminium derivatives may be made by the reaction of [Hg(SiMe3)2] with Mg turnings or Al powder,6' and have not yet been exploited fully as synthetic reagents. 2PbC1 + 2[Mg(SiMe3),J Et70* [Pb(SiMe3),J+ Pb + 2MgCI2 (6) 6 Group V As usual much of organoarsenic chemistry is directed at the synthesis of ligands for transition-metal complexes.An interesting example of these is the strained small-ting species [Ph2As2C2Ph2] (23). This is formed in the reaction of the cyclohexa- arsane species [(AsPh),] with excess PhCECPh which gives a 13.5% yield of the tetraphenyldiarsetine product. In this compound the interarsenic distance is 247 pm the intercarbon 136 pm and the arseniocarbon 196 pm.W Some reactions with transition-metal complexes have been investigated. Ph ph\ c=c / I\ ,As-As Ph 'Ph In terms of organoarsenic chemistry proper the principal innovations also appear to be in the area of multiply bonded chemistry. The first unsupported diarsene [(~,~,~-BU'~C,H,)AS=AS{CH( SiMe,),)] has been made by the reaction between [(2,4,6-Bu1,C6H2)hH2] and (Me2Si)2CHAsC12.67 The interarsenic distance is 222.4(2) pm and the angles AsAsC which average at 96.7(3)" are smaller than angles PPC in similar diphosphenes.Double bonds to phosphorus from both arsenic and antimony have been made similarly by the reactions of [(Me3Si)2CHMC12] (M= As or Sb) with [(2,4,6-Bu',C6H2)PH,] in the presence of DBU in THF. The products (~,~,~-Bu',C~H~)P=MCH(S~M~,)~ are orange crystalline compounds. The 63 T. N. Mitchell J. Organornet. Chem. 1983. US,279. 64 L. Rosch and U. Starke Angew. Gem Inr Ed EngL 1983. 22 557. 65 D. W. Goebel J. L. Hencher and J. P. Oliver Oganornetullics 1983 2 746. 66 G. Sennyey F. Mathey J. Fischer and A.Mitschler Orgonornetollics 1983 2 298. 67 A. H. Cowley J. G. Lasch N. C. Norman and M. Pakulski J. Am. Chem Soc.. 1983. 105. 5506. 304 J. D. Kennedy new starting stibine [(Me3Si)2CHSbC12] was prepared by treatment of SbCl with [( Me3Si)2CHMgC1] in Et20 solution.68 Other arsenic multiply bonded chemistry reported in 1983 includes some work on the aromatic 1 H-1,3-benzarsa~oles.~~ In contrast to the arsabenzenes these .rr-excess species can be alkylated at the arsenic atom as well as lithiated at positions shown in (24) and (25) without a high incidence of lithium reagent addition across the As=C double bond. Alkylations and acylations of the ambident 1-1ithio-deriva-tives (24) and substitution reactions of 2-lithiobenzazarsole species have been de~cribed.~~ Li R (24) (25) There is continuing interest in tetraorganyl-distibines and dibismuthines much of which is stimulated by the thermochromic properties of these Various tetravinyldistibines [R$b2] have been made uia the scheme in equation (7).These are generally yellow in the liquid phase but where R = CH2=CH the compound freezes to a violet solid. When R = isopropenyl an brange solid is formed.70 M(NaorK) CH ClCH CI R,Sb -R,SbM -R,SbSbR (7) N" A variety of dibismuthines has now been made; all are red in solution but the tetramethyl and tetraisopropenyl derivatives together with the bi(bismuthacyc1open- tyl) species (26) freeze to give blue solids.71 Tetraphenyldibismuth is the first crystallographically determined tetraorganyl deri~ative.~~ It is made in 50% yield as an orange solid by the reaction of Ph2BiC1 and Na in NH solution.At liquid nitrogen temperatures it is yellow and the solid-state structure has no significant intermolecular interbismuth interactions. The molecule has a staggered transoid conformation (27) ; all angles approximate to right angles indicating lone-pair s-~haracter.~~ 'I Bi'LBi I' Two other aspects of organobismuth work have been noted in 1983. The first is the synthesis of the metallochiral triorganobismuthines [BiAr'Ar2Ar3]. These are formed by the cleavage of [BiAr1Ar2,] with HBr in methanol to give [BiAr'Ar2Br] 68 A. H. Cowley J.G. Lasch N.C. Norman M. Pakulski and B. R. Whittlesey J. Chem. SOC.,Chem. Commun. 1983 881. 69 J.Heinicke A. Petrasch and A. Tzschach J. Organornet. Chem. 1983 258 257. 70 A. J. Ashe E. G. Ludwig and H. Pommerening Organornetallics 1983 2 1573. 7' A. J. Ashe E. G. Ludwig and J. Oleksyszyn Organometallics 1983 2 1859. 72 F. Calderazzo A. Morvillo G. Pelizzi and R. Poli J. Chem. SOC.,Chem. Commun. 1983 507. 73 H. J. Breunig and D. Muller J. Organornet Chem. 1983 253 C21. 74 H. J. Breunig and D. Miiller Z. Naturforsch. B Anorg. Chem. Org. Chem. 1983 38 125. 305 Organometallic Chemistry -Part (ii) Main-Group Elements followed by treatment with an appropriate Grignard reagent [eMgBr]. The results suggest stable pyramidal structures but enantiomers have not yet been resol~ed.~' The second is the characterization of the six-co-ordinate species [Ph,BiX( MeOx)] (X = halogen MeOx = methyloxinate) which are readily made in yields of 40-70% from [Ph3BiX2] and Na[MeOx].The compounds can be regarded as a straight- forward octahedral bismuth(v) complexes (28) although the B-N bond is readily cleaved in polar solvents which can result in decornp~sition.~~ 7 Group VI Organotellurium chemistry continues to be a lively area both from the chemical and from biological and biomedical points of view. Structural work of note includes the observation uia X-ray diffraction at low temperatures of tellurium(1v) lone-pair and bonding electron-density in Me2TeC1,.77 Reassuringly the results are consistent with classical bonding models for AB4E compounds and there is also support for a donor-acceptor bonding model involving C1 lone-pair density and an empty Te orbital.Organotellurium compounds in synthesis continue to be of importance. One example is their use in the synthesis of a number of olefins allylic alcohols and allylic ethers in a process facilitated by the ready elimination of s-alkylphenyl- telluroxides from the product prec~rsors.~~ A novel involvement of tellurium is in the formation of benzylic chlorides by rearrangement of cycloheptatrienes [equation (8)~'~ 0 R' R2 I \-TeC'a @\ :HCl + {TeCl,} - R3 R' Another interesting organotellurium reaction involves the compound 2,Sdiphenyl- 1,6-dioxa-6a-tellurapentalene(29) which is prepared by reaction (9)." This species oxidatively adds Br or C1 at low temperatures to give the 12-Te-5 pertelluranes (30).These last species can function as mild oxidants and they are also of interest 75 P. Bras A. van der Gen abd J. Wolters J. Organornet Chem. 1983 256 CI. 76 G. Faraglia R. Graziani L. Volponi and U. Casellato J. Organornet. Chem. 1983 253 317. 77 R. F. Ziolo and J. M.Troup J. Am. Chew. SOC.,1983 105 229. 78 S. Uemura and S. Fukuzawa J. Am. Chem. SOC.,1983 105 2748. 79 M. Albeck T. Tamari and M. Sprecher. J. Org. Chem. 1983,48 2276. 80 M. R. Detty and H. R. Luss J. Org. Chem. 1983,48 5149. J. D. Kennedy in that structural studies indicate some intermolecular tellurium-halogen interaction (e.g. Te-e-Br ca. 355 pm) in addition to the direct bonding (average Te-Br 256 pm).80 CI -Te-O' 0 II uph + PhCCl + NEt, Me 0-Te-0 Ph Ph (9) O-pTe-;) Ph U '' Ph There is also interest in mechanistic work.To cite one example the stereochemistry of the addition of TeCl and of [(2-naphthyl)TeC13] to a variety of linear olefins has been studied.81 In this work [(naphthyl)TeC13] ia found to add completely anti-stereospecifically whereas TeC14 gives syrt and anti mixtures. In these reactions p-benzoquinone is highly effective in promoting syn-addition when present in catalytic amounts of 15-20%. The results have been taken to suggest an ionic mechanism involving a telluronium ion intermediate for [(2-naphthyl)TeC13] whereas competing syn-addition and free-radical chain reactions are proposed for the TeCl processes.'' *' J.-E. Backvall J.Bergman and L. Engman,J. 0%.Chem. 1983.48 3918.