9 Organometallic Chemistry Part (ii) Main-Group Elements By P. D. LlCKlSS Department of Chemistry and Applied Chemistry University of Salford Salford M5 4WT Main-group organometallic chemistry continues to thrive with the fields of multiple bonding between heavier main-group elements and reactive intermediate chemistry continuing to grow and ‘precursor’ chemistry in which novel organometallic monomers are prepared as precursors to either ceramic materials or polymers is becoming a field in its own right. Vigorous growth also continues in the field of preparation and characterization of unusual organolithium reagents. A new book’ gives excellent coverage of most aspects of main-group chemistry. The format of this Report is the same as that of last year concentrating mainly on new structural features and novel or potentially useful reactions.Once again much of interest has been excluded because of the limited space available. 1 Group I Three new indicators N-pivaloyl-o-toluidine,2 N-pivaloyl-o-benzylamine,2and PhTeTePh,3 are proposed as reagents for the direct titration of organolithium reagents. The compounds are all stable simple to prepare give sharp end points and should prove useful to those who regularly titrate for example commercially supplied Bu”Li. The cleavage of THF by organolithium reagents is a common problem and has often limited the situations in which this very useful solvent can be used. Such cleavage is greatly reduced by the addition of Mg(CH2CH20Et) to the reaction solution allowing for example Bu‘Li and C6H11Li to be prepared readily in THF.4 The investigation of organolithium reagent structure by X-ray crystallography and NMR spectroscopy continues to reveal various novel structural features.Fast- atom-bombardment mass spectrometry has also been used to determine the degree of aggregation of RLi compound^.^ The first structural characterization of a non- conjugated 1,2-dilithioethane has been carried out.6 Treatment of tetrakis (trimethyl- sily1)ethylene with lithium metal affords 1,2-dilithio[tetrakis(trimethylsilyl)]ethane which can be isolated as a yellow crystalline THF adduct. The lithium atoms are ’ Ch. Elschenbroich and A. Salzer ‘Organometallics’ VCH Weinheim FRG 1989. J. Suffert J. Org. Chem. 1989,54 509. Y. Aso H.Yamashita T. Otsubo and F. Ogura J. Org. Chem. 1989 54 5627. C. G. Screttas and B. R. Steele J. Org. Chem. 1989 54 1013. A. K. Abdul-Sada A. M. Greenway and K. R. Seddon J. Organomet. Chem. 1989 375 C17. ‘A. Sekiguchi T. Nakanishi C. Kabuto and H. Sakurai J. Am. Chem. SOC.,1989 111 3748. 261 262 P. D. Lickless each coordinated to the two central carbons and an oxygen of a THF molecule the average C-C bond length is 1.597 A. The solid-state structure of 1-1ithio-2-methoxybenzene' consists of tetrameric units in which the four lithium atoms form a pyramid with a lithiated arylcarbon being found above each triangular face and bonded to the three lithium atoms forming the face. There also appeardo be short Li...HC interactions between a lithium and an aryl hydrogen in a different tetramer.Use of 6Li NMR spectroscopy shows that the tetrameric structure remains intact in toluene-d solution but on addition of TMEDA dimers are formed and addition of N,N,N',N',N"-pentamethyldiethyl-enetriamine leads to monomer formation. In the solid 1,l-bis[ (dimethyl- amino)methyl]-2-propyllithium' comprises dimeric units in which the lithium atoms are in an Li2C ring and are also coordinated to dimethylamino groups. In n-pentane- d12solution two dimeric species are present the major one appears to have the same structure as that in the solid state (in which the a-methyl groups are trans to each other) while the minor one is very similar but has the a-methyl groups in a cis arrangement. The first trimeric organolithium compound [2.6-bis(dimethyl- amino)phenyl]lithium has been characterized in both solid and solution states.The solid-state structure comprises a triangle of lithium atoms bridged by aryl carbanions with the NMe substituents being intramolecularly coordinated to the lithium atoms. In non-polar solvents such as toluene the trimeric structure is also favoured but in THF a monomer-trimer equilibrium OCCU~S.~ Both 2-lithiobenzofuran-TMEDA and 2-lithiobenzothiophene-TMEDA are dimeric in the solid state with benzofuryl rings bridging the lithium atoms and TMEDA acting as a chelating ligand. NMR spectroscopy also shows both com- pounds to be dimeric in solution." Surprisingly both the solid- and solution-state structures of Ph2PCH2Li-TMEDA have been shown" to be monomeric with the lithium being only three-coordinate bonded to the CH group and chelated by the TMEDA.Several a -or y-phosphorus functionalized alkyllithiums e.g. [(Li(TMEDA)(CH,PMeR)},] (R = Me or Ph) have been prepared by addition of Bu"Li to the appropriate phosphine.12 The solid-state structure of the benzyllithium adduct [q1-C6H5CH2]Li.THF.TMEDA has been found (in contrast to other adducts which are polymeric) to be monomeric with the lithium being coordinated to only the benzylic carbon of the benzyl group the oxygen of the THF molecule and the two nitrogens of the TMEDA molec~le.'~ Treatment of Me,SiCH2CN with either Bu"Li or Pr:NLi affords Li2( Me,SiCCN) (A) which co-crystallizes from the reaction solution together with one molecule ' S.Harder J. Boersma L. Brandsma G. P. M. van Mier and J. A. Kanters J. Organomet. Chem. 1989 364,1. W. Moene M. Vos F. J. J. De Kanter G. W. Klurnpp and A. L. Spek J. Am. Chem. SOC.,1989 111 3463. S. Harder J. Boersma L. Brandsma J. A. Kanters W. Bauer and P. von R. Schleyer Organomefallics 1989 8 1696. lo S. Harder J. Boersma L. Brandsma J. A. Kanters W. Bauer R. Pi P. von R. Schleyer H. Schollhorn and U. Thewalt Organometallics 1989 8 1688. G. Fraenkel W. R. Winchester and P. G. Willard Organometallics 1989 8 2308. 12 L. T. Byrne L. M. Engelhardt G. E. Jacobsen W.-P. Leung R. I. Papasergio C. L. Raston B. W. Skelton P. Twiss and A. H. White J. Chem. SOC.,Dalfon Trans. 1989 105. 13 W. Zarges M. Marsch K. Harms and G. Boche Chern. Ber.1989 122 2303. Organometallic Chemistry-Part (iii) The Main-Group Elements 263 of hexane as the complicated aggregate [(A)12(Et20)6(C6H14)],14 a structure significantly different to monolithium nitriles. Several silyllithium reagents have been investigated with the X-ray crystal struc- ture of (thf),Li(SiPh,),Li(thf) being determined15 and treatment of 2,4,6-tri-t- butylphenyllithium with halogenosilanes affording LiSiC1 .16 The bulky (mesityl),HSiLi(thf) can be prepared as a useful reagent by treatment of (mesityl),SiHCl with lithium powder.17 Methylenecyclopropane reacts with lithium powder to give the stable dilithium reagent 2,4-dilithio but- 1-ene rather than the trimethylenemethane dianion.18 The new lithium reagent Me,SiCHLiSi(OMe)Me can readily be prepared by treatment of the parent hydrocarbon with Bu'Li.The reagent effects direct conversion of enolizable or non-enolizable aldehydes and ketones into synthetically useful vinyl- silanes and promises to be a useful alternative to (Me3Si),CHLi which is only suitable for non-enolizable substrates.'' The radical anion reductive metallation of phenyl thioethers to give organolithium compounds has been reviewed.,' Reductive lithiation of (RO),( PhS)CH species and transmetallation of (RO),( Bu;Sn)CH com-pounds both yield the previously unavailable simple (dialkoxymethy1)lithium reagents (RO),CHLi (R = Me Et etc.) which are useful as one-carbon nucleophiles.21 The reaction of [( Me3Si),C5H2]Li and related lithium reagents with various Lewis bases such as ethers amines and thioethers affords crystalline adducts which are monomeric in solid solution and gas phases., In the solid state there is an unusual almost linear arrangement of the ring centroid of the cyclopentadienyl group the lithium and the oxygen of the THF molecule in [(Me3Si)3C5H2]Li-THF.The disodium compound [Ph,CCPh2]Na2.(OEt2) is formed as a green solid when Ph2C=CPh2 is treated with sodium metal. The solid-state structure of the compound is complicated with the two sodium atoms in different environments one in which the sodium is sandwiched between four aryl rings two from one dianion and two from a second and another in which the sodium coordinates with two ether molecules and one diani~n.,~ Another sodium reagent [PhNa( PMDTA)] ,in contrast to its monomeric lithium analogue LiPhSPMDTA has a dimeric structure with the ips0 carbons of the phenyl rings and the sodium atoms forming a four-membered ring and each sodium being coordinated by a single PMDTA.24 The organopotassium compound K[ q5-C5(CH2Ph)5].3THF has been prepared by treatment of pentabenzylcyclopentadiene with potassium.X-Ray crystallography gives a K-C(ring) average distance of 3.035& somewhat shorter than that in KCH (3.22 A) but similar to that in K[C5H4SiMe,] (3.00 14 W. Zarges M. Marsch K. Harms and G. Boche Chem. Ber. 1989 122 1307. l5 G. Becker H. M. Hartmann E. Hengge and F. Schrank 2. Anorg. AZZg. Chem. 1989 572 63. 16 H. Weiss and H. Oehme 2. Anorg. AZlg. Chem. 1989 572 186. D. M.Roddick R. H. Heyn and T. D. Tilley Organometallics 1989 8 324. 18 A. Maercker and K.-D. Klein Angew. Chem. Znt. Ed. EngZ. 1989 28 83. 19 T. F. Bates and R. D. Thomas J. Org. Chem. 1989 54 1784. 20 T. Cohen and M. Bhupathy Ace. Chem. Res. 1989 22 152. 21 C. S. Shiner T. Tsumoda B. A. Goodman S. Ingham S.-H. Lee and P. E. Vorndam J. Am. Chem Soc. 1989 111 1381. 22 P. Jutzi W. Leffers S. Pohl and W. Saak Chem. Ber. 1989 122 1449. 23 H. Bock K. Ruppert and D. Fenske Chem. Ber. 1989 122 1685. 24 U. Schiimann U. Behrens and E. Weiss Angew. Chem. Znt. Ed. EngZ. 1989 28 476. 25 J. Lorbeth S.-H. Shin S. Wocadlo and W. Massa Angew. Chem. Znt. Ed. EngZ. 1989 28 735. 264 P. D. Lickless 2 Group I1 The first two-coordinate organomagnesium compound ( Me3Si)3C-Mg-C(SiMe3)3 to be characterized in the solid state has an Mg-C bond length of 2.116(6) % and a linear C- Mg-C arrangement.26 A second unsolvated alkylmagnesium species [(Np2Mg)2-(NpMgBr)2], (Np = Me3CCH2) can be prepared by reaction of NpBr with magnesium in ether and has the polymeric structure shown in Scheme 1.27 Scheme 1 Several novel sodium organomagnesates e.g.[ Na(PMDTA)],[MgPh,] (1) and Na2[ Mg(C-CBu'),(TMEDA),] (2) have been prepared and characterized by X-ray crystallography.** Compound ( 1) has tetrahedral geometry at magnesium with the phenyl groups forming unsymmetrical bridges between magnesium and sodium and (2) has tram alkynyl groups coordinated to magnesium in a pseudo-octahedral environment. Each four-membered ring is perpendicular to its neighbours and the rings are unsymmetrical having Mg-C bonds between 2.20 and 2.42 A.Another example of an X-ray crystal structure determination of an alkylmag- nesium compound is [ v3-HB(3-Bu'pyz),]MgMe which can be prepared by treatment of Me2Mg with T1[ HB(3-B~'pyz)~l.~~ Surprisingly when treated with 13CH31 the methylmagnesium compound not only gives the alkylation product I3CH3CH3but also the MgL3CH3 derivative derived from alkyl exchange. The role of free radicals in the mechanism of Grignard reagent formation has been further studied and firm evidence provided that radicals are strongly adsorbed onto the magnesium metal surface and are therefore not free to diffuse in solution readily.30 A detailed study of the reaction between cycloheptyl bromide and mag- 26 s.s. Al-Juaid C. Eaborn P. B. Hitchcock C. A. McGeary and J. D. Smith J. Chem. Soc. Chem. Commun. 1989 273. 27 P. R. Markies G. Schat 0.S. Akkerman F. Bickelhaupt W. J. J. Smeets A. J. M. Duisenberg and A. L. Spek J. Organomet. Chem. 1989 375 11. 28 M. Geissler J. Kopf and W. Weiss Chem. Ber. 1989 122 1395. 29 R. Han A. Looney and G. Parkin J. Am. Chem. Soc. 1989 111 7276. 30 H. M. Walborsky and J. Rachon J. Am. Chem. Soc. 1989 111 1896. Organometallic Chemistry-Part (iii) The Main-Group Elements 265 nesium in ether provides clear evidence that cycloheptyl radicals are intermediates in the formation of cycloheptylmagnesium bromide.31 However the data could not be used to prove that the intermediate radical was not bound to the metal surface.The use of highly active magnesium allows convenient preparation of but-2-ene- 1 4-diylmagnesium compounds which are not readily available using conventional techniques and which can be used to prepare various useful cyclic products.32 The use of substituted cyclopentadienyl ligands has allowed the successful prepar- ation and structural characterization of several new organocalcium complexes. Thus treatment of Ca12 with MeSCSK results in the formation of a mixture of (77'-MeSC5)CaI(THF) and (775-Me5C5)2Ca(THF)2, from which the former can readily be isolated.33 The solid-state structure is dimeric with iodines bridging between calciums each of which is coordinated to one Me& and two THF ligands.The and complexes (775-Me5C,)2Ca.2THF [q5-1,3-(Me3C)2CSH3]2Ca-THF,[77'-(Me3Si),C5H5-,]2Ca-THF(n = 1or 2) have been prepared by treatment of calcium in liquid ammonia with the parent cyclopentadiene. X-Ray crystallography of [q5-(Me3Si),C5H312Ca.THF shows that the compound is a monomeric bent metal- locene with a THF molecule coordinated to the calcium.34 The bent metallocene structure has also been found in [qS-MeCSH4]2Ca.DME in which both DME oxygens are coordinated to the calcium.35 Co-condensation of metals Ca Sr or Ba with cyclooctatetraene (COT) and THF at -196 "C leads to formation of M(COT)(THF) species which decompose to give M(C0T) when heated to 60°C in U~CUO.~~ It is thought that the metal is bound to the ligand in a polyhapto fashion with the observed low solubility suggesting a polymeric structure.Treatment of calcium in liquid ammonia with COT also gives C a( C OT) .35 3 Group I11 Treatment of A12Br6 at -10°C with Bu'Li affords a mixture of [HAlBu:], [LiHAlBu:I2 and AlBu;. On treatment with further Bu'Li AlBu affords Li[AlBu\]. Both of the aluminium hydrides have been examined by X-ray crystallography; [HAlBu\] contains a planar six-membered Al-H ring while in [LiHA1Bu:l2 there are two lithium atoms bridging between the Al-hydrides to form an H2Li2 cyclic dimer.37 The reaction between ammonia and Me3AI and BuSAl gives the trimeric species [Me2A1NH2I3 and [BuiA1NH2l3 respectively both of which are potential precursors to aluminium nitride.38 Although the methyl derivative has a skew-boat ring conformation the tertiary butyl derivative has an unprecedented planar (AlN)3 ring which is presumably required to minimize 1,3-interactions between the bulky substituents on aluminium.The thermal decomposition of BuiAl above 470 K 3' K. S. Root C. L. Hill L. M. Lawrence and G. M. Whitesides J. Am. Chem. SOC.,1989 111 5405. 32 H. Xiong and R.D. Rieke J. Org. Chern. 1989 54 3247. 33 M. J. McCormick S. C. Sockwell C. E. H. Davies T. P. Hanusa and J. C. Huffman Organometallics 1989 8 2044. 34 P. Jutzi W. Leffers G. Muller and B. Huber Chem. Ber. 1989 122 879. 35 A. Hammel W. Schwarz and J. Weidlein. J. Organornet. Chern. 1989 378 347. 36 D. S. Hutchings P. C. Junk W. C. Patalinghug C. L. Raston and A. H. White J.Chern. SOC.,Chem. Cornrnun.,1989 973. " W. Uhl 2. Anorg. Allg. Chem. 1989 570 37. 38 L. V. Interrante G. A. Sigel M. Garbauskas C. Hejna and G. A. Slack Znorg. Chem. 1989 28 252. 266 I? D. Lickless proceeds via P-hydride elimination on an aluminium surface to give hydrogen isobutylene and a carbon-free crystalline layer of aluminium. This may therefore be a useful way to form A1 layers on electronic devices.39 Infrared spectra of matrix-isolated species provide the first good experimental evidence for an Me3Ga.AsH3 adduct the formation of which is usually proposed as the first step in the chemical vapour deposition of G~As.~' The chemistry of aminoalanes continues to attract considerable interest. The first six-coordinate alkylaluminium compound (3) has been prepared by treatment of Me,Al with N(CH,CH,OH) and comprises an A1406 array containing two six- coordinate and two four-coordinate aluminium atoms.41 A six-coordinate aluminium with octahedral coordination is also found in the product (4) of the reaction between 1,4,8,1l-tetraazacyclotetradecaneand Me3Al in the presence of ZrC14 .42 Me Me / \ Me Me Me/ 'Me (3) (4) Tetradentate amines also react with alkylaluminium compounds to form aminoalanes (5) and (6) containing Al,N and Al,NO four-membered rings and a central six-coordinate al~minium.4~ The reaction of Me3A1 with 3,3'-iminobispropy- lamine affords (7) as the sole product in which four organoaluminium units bridge between two amine ligands.44 39 B.E. Bent R. G. Nuzzo and L. H. Dubois J. Am. Chern. SOC.,1989 111 1634. 40 E. A. Piocos and B. S. Auk J. Am. Chem. Soc. 1989 111 8978. 41 M. D. Healy and A. R. Barron J. Am. Chem. Soc. 1989 111 398. 42 G. H. Robinson M. F. Self S. A. Sangokoya and W. T. Pennington J. Am. Chem. SOC.,1989,111,1520. 43 S. A. Sangokoya F. Moise W. T. Pennington M. F. Self and G. H. Robinson Orgunometullics 1989 8 2584. 44 G. H. Robinson F. Moise W. T. Pennington and S. A. Sangokoya Polyhedron 1989 8 1279. Organometallic Chemistry-Part (iii) The Main-Group Elements 267 Treatment of Me3Ga and Me,In with Me,Si-N=C=N-SiMe affords volatile 1 1 adducts but Me,AI gives a monomeric insertion product Me2Al( NSiMe,),CMe which contains a planar AlN2C ring system.45 Treatment of R3AI compounds (R = Me or Et) with (-)-ephedrine affords novel five-coordinate aluminium com- plexes in which the formation of the Al-N bond is stereospecific and leads to optical activity at the nitrogen while treatment with pyridine-2-thiol (PySH) affords crystalline head-to-head dimers [ R2AlPyS]2.47 Treatment of mesitylgallium derivatives with Cr(C0)6 or Mo(CO) leads to formation of a variety of metal complexes in which one or more M(CO) units are coordinated to mesityl groups; for example [(CO),Mb( q6-C6Me3H2),]Ga(C6Me3H2)3-n1 or 2).48 (n = The unusual tetraalkyl digallane and diindane derivatives [ { ( Me3Si),CH),Ml2 containing metal-metal bonds have been prepared by treating either Ga2Br4.2( dioxane) or In2Br4.2TMEDA with four equivalents of ( Me,Si),CHLi.The gallium compound forms yellow crystals with a Ga-Ga bond distance of 2.541 b~~~ while the indium analogue is orange-red and has an In-In bond length of 2.828 A." A series of '111-V' compounds (Me21nNR2) (R = Et Pri or Me,Si) and (M~,IIIPR~)~= But or Ph) have been prepared and shown to be dimeric in both (R the vapour and solid phase.'l Mass spectral studies indicated that increasing the size of the R group leads to a decrease in stability. The dimeric [Et,InPBu\] has also been structurally ~haracterized,~ again demonstrating the use of bulky ligands in reducing the degree of molecular association in organometallic compounds. The steric effects of the bulky mesityl group on the structures of arylindium compounds has been in~estigated.~ Trimesitylindium forms discrete monomers in the solid state with a possible agostic interaction between an ortho CH and indium the anion in [ Me,N][InCl(mesityl),] is also a discrete unit with a distorted tetrahedral geometry around indium and InCl(mesityl) forms centrosymmetric chloride-bridged dimers.Benzylindium compounds In(CH2Ph),C13- (n = 1 2 or 3) have been pre- pared.54In solution and in the vapour phase In(CH,Ph) exists as monomers while [ In(CH2Ph),C1] and [In( CH2Ph)C12] , probably contain chloride bridges. Several isopropylindium derivatives PriInCI Pr'InC1 and [ Pr\InNHBu'] have been pre- pared55 in the continuing search for simple molecules which may be used as precursors to indium in chemical vapour deposition processes.Neopentylindium compounds Np,In Np,InCl NpInCl, and Np,InMe (Np = Me3CCH2) have also been prepared using the reaction between NpMgCl and InI as a starting point. 45 R. Lechler H.-D. Hausen and J. Weidlein J. Organornet. Chern. 1989 359 1. 46 M. L. Sierra V. S. J. de Mel and J. P. Oliver Organornetallics 1989 8 2486. 47 R. Kurnar V. S. J. de Mel and J. P. Oliver Organornetullics 1989 8 2488. 48 0. T. Beachley jun. T. L. Royster jun. W. J. Youngs E. A. Zarate and C. A. Tessier-Youngs Organornetallics 1989 8 1679. 49 W. Uhl M. Layh and T. Hildenbrand J. Organornet. Chern. 1989 364,289. 50 W. Uhl M. Layh and W. Hiller J. Organornet. Chern. 1989 368,139. 5' K. A. Aitchison J. D. J. Backer-Dirks D. C. Bradley M. M. Faktor D.M. Frigo M. B. Hursthouse B. Hussain and R. L. Short J. Organornet. Chern. 1989 366,11. 52 N. W. Alcock I. A. Degnan M. G. H. Wallbridge H. R. Powell M. McPartlin and G. M. Sheldrick J. Organornet. Chern. 1989 361 C33. 53 J. T. Lernan and A. R. Barron Organornetallics 1989 8 2214. 54 A. R. Barron J. Chern. SOC. Dalton Trans. 1989 1625. 55 B. Neurniiller Chern. Ber. 1989 122 2283. 268 P. D. Lickless X-Ray crystallography shows that NpInC12 is a one-dimensional polymer [NpIn (p-Cl),lm with no interactions between polymer strands.56 Surprisingly reaction of alkylindium compounds such as Me,In and Et,In with alkyliridium complexes leads to In-C cleavage with addition products being formed. For example IrMe(PMe,) and InMe afford rner and fuc isomers of IrMe2(PMe,),(InMe2).57 Intramolecular coordination of the two nitrogen atoms to indium in Me[2,6- (Et2NCH2),C6H3]InC1 allows monomeric units with a distorted trigonal-bipyramidal geometry to be formed.,* The first example of a stable (alky1peroxo)indium com- pound Bu',InOOBu' can be prepared by the controlled addition of O2 to Bu~I~.,~ The compound is resistant to further oxidation and comprises dimers with bridging Bu'OO groups.Treatment of [2.2] paracyclophane with In[InBr,] or Tl[GaCl,] yields 1 1 adducts ( p-C6H,CH,CH2),.In[ InBr,] and (p-C6H4CH2CH2)2.fl[Gac14],respectively.60 q. Both compounds form sM(paracyc1ophane) M(paracyc1ophane)M. -one-dimensional stacks and are of high thermal and chemical stability. The solid- and gas-phase structures of the golden-yellow ($-C,Me,)In have been investigated.61 The gas-phase structure consists of monomers with the indium situated 2.288A above the ring centroid while in the solid state the structure comprises hexameric units with the six indium atoms forming an octahedral array with the Me,CF ligands coordinated around the outside with an indium-ring centroid distance of 2.302 A.The structure of [q5-(PhCH2),C5]In was found62 to be isostruc- tural with its thallium analogue comprising 'quasi-dimers' with an inversion centre between the two indium atoms and an In.-In distance of 3.631 A. Evidence for a Tl'-Tl' interaction in [(PhCH,),C,TI] is also supported by an MO analysis of the Treatment of TlCl with arylsilver reagents AgR (R = mesityl C6F3H2 or C6F5) affords complexes of the types [TlR2][T1C13R] TlClR, or TlR3 depending on the molar ratio of reagents used and the R The X-ray crystal structure of [Tl(mes),][T1C13(mes)] shows the linear [Tl(me~)~]+ cations and the tetrahedral [TlCl,(mes)]-anions to be linked by weak Tl-..Cl interactions into chains.4 Group IV Organosilicon chemistry is covered well in two new volumes65 and the crystal structure data for silicon compounds have also been the subject of a book.66 The 56 0.T. Beachley jun. E. F. Spiegel J. P. Kopasz and R. D. Rodgers Organometallics 1989 8 1915. 51 D. L. Thorn and R. L. Harlow J. Am. Chem. SOC.,1989 111 2575. 58 H. Schumann W. Wassermann and A. Dietrich J. Organomet. Chem. 1989 365 11. 59 W. M. Cleaver and A.R. Barron J. Am. Chem. SOC.,1989 111 8966. 60 H. Schmidbaur W. Bublak B. Huber J. Hofmann and G. Muller Chem. Ber. 1989 122 265. 61 0. T. Beachley jun. R. Blom M. R. Churchill K. Faegri jun. J. C. Fettinger J. C. Pazik and L. Victoriano Organometallics 1989 8 346. 62 H. Schumann C. Janiak F. Gorlitz J. Loebel and A. Dietrich J. Organomet. Chem. 1989 363 243. C. Janiak and R. Hoffmann Angew. Chem. In?. Ed. Engl. 1989 28 1688. 64 A. Laguna E. J. FernLndez A. Mendia M. E. Ruiz-Romero and P. G. Jones J. Organomet. Chem 1989,365 201. 65 'The Chemistry of Organic Silicon Compounds' ed. S. Patai and Z. Rappoport John Wiley Chichester 1989. 66 E. Lukevics 0. Pudova and R. Sturkovich 'Molecular Structure of Organosilicon Compounds' Ellis Horwood Chichester 1989.Organometallic Chemistry-Part (iii) The Main-Group Elements 269 chemistry of the Si-C bond for 198667 and 198768 has been reviewed as has the ‘direct synthesis’ of chlor0silanes,6~ the synthesis and synthetic potential of acyl- ~ilanes,~’ the steric effect of the Me3Si group in organic chemistry,” p~lysilanes,~~,~~ cyclic silicon germanium and tin comp0unds,7~ and molecular states of silicon corn pound^.^^ The addition of catalytic amounts of cyanide or thiocyanate salts such as CuCN or [Bu$N]+[SCN]- greatly promotes the reaction between Grignard reagents and chlorosilanes. For example after aqueous work up the reaction between PhSiC13 and (C6Hll)MgBr in the presence of 5% CuCN at -30°C affords 83% of PhSi(C6Hl,)20H,76 and Ph,SiCl and Bu‘MgC1 in the presence of CuCN give Ph,Bu‘SiCl in 80% yield after 5 h at reflux in THF.77 This promises to be a convenient way to improve the synthesis of simple organosilanes that are finding increasing use in organic synthesis.It has been shown that unprecedented 1,3-migration of a silyl group occurs in the 6,6-bis(trimethylsilyl)norborn-2-y1cation prior to desilylation and deprotonation. This presumably occurs via a rapidly equilibrating mixture of carbocati~ns.~~ The formation of 1,3-aryl-bridged silicocations for which there seems to be no analogue in carbon chemistry is proposed in the reactions of compounds of the type (Me3Si),C(SiMe2C6H4X)(SiMe21)= H p-OMe or p-Me) in which the y-aryl (X groups provide powerful anchimeric assistance in solvolysis reactions with for example CF3CH,0H.79 The use of chiral silanes for asymmetric induction continues to be studied.Little success has so far been achieved although the use of chiral silanes in which the chiral centre is remote from the silicon has been demonstrated to be highly enan- tioselective in the synthesis of arylcarbinols.80 Reaction of RCH=C=C (R = Me or But) with chiral naphthylphenylmethylsilaneleads to formation of chiral allenes with 3.5 and 10.5% enantiomerk excess respectively.81 Reaction of RLi reagents (R = Me But Ph etc.) with the chiral silyl thioketone (R)-(-)-Me(a-naph- thyl)PhSiC(S)Ph gives after protic work up silyl sulphides Me( a-naph- thyl)PhSiC(SR)HPh with up to -50% diastereomeric excess depending on the conditions used.82 Chiral silanes have also been used in the preparation of homoally- lic alcohols in up to 55% e.e.83 67 G.L. Larson J. Organomet. Chem. 1989 360,39. 68 G. L. Larson J. Organomet. Chem. 1989 374 1; M. P. Clarke ibid. 1989 376 165. 69 G. L. Larson J. Organomet. Chem. 1989 374 1. 70 A. Ricci and A. Degl’Innocenti Synthesis 1989 647. 71 J. R. Hwu Chem. Rev. 1989 89 1599. ’* R. D. Miller and J. Michl Chem. Rev. 1989 89 1359. 73 R. D. Miller Angew. Chem. Znt. Ed. Engl. 1989 28 1733. 74 P. D. Lickiss in ‘Rodd’s Chemistry of Carbon Compounds’ ed. M. F. Ansell Elsevier Amsterdam 1989 Vol. IVK p.1. 75 H. Bock Angew. Chem. Znt. Ed. Engl. 1989 28 1627. 76 P. J. Lennon D. P. Mack and Q. E. Thompson Organometallics 1989 8 1121.77 A. Shirahata Tetrahedron Lett. 1989 30,6393. 78 W. Kirmse and F. Sollenbohmer J. Am. Chem. Soc. 1989 111 4127. 79 C. Eaborn K. L. Jones and P. D. Lickiss J. Chem. Soc. Chem. Commun. 1989 595. 80 T. H. Chan and P. Pellon J. Am. Chern. Soc. 1989 111 8737. P. J. Stang and A. E. Learned J. Org. Chem. 1989 54 1779. 82 B. F. Bonini G. Maccagnani S. Masiero G. Mazzanti and P. Zani Tetrahedron Lett. 1989 30,2677. 83 T. H. Chan and D. Wang Tetrahedron Lett. 1989 30,3041. 270 P. D. Lickless Hydrolytic condensation of cyclohexyltrichlorosilanein aqueous acetone affords a mixture of silasesquioxanes which have structural similarities to silica surfaces and which may be useful models for such surface^.'^*^^ The tetrasiloxane {OSi[ (CH2),OHI2} appears to be the first diorganofunctional cyclosiloxane that is completely miscible with water but it could not be polymerized by ring opening with H2S04 .86 The reaction of trans-( PhMeClSi)CH=CH( SiPhMeCl) with sodium under the influence of ultrasonic irradiation produced a polymer (Mw 39 800) trans-[(PhMeSi)CH=CH(SiPhMe)l,.The polymer's Si-Si bonds are broken under irradiation by a mercury lamp and it can be cast as a film which can be doped with SbF vapour to give a highly conducting polymer film." Polymerization of 1,2- diethynyldisilanes catalysed by RhCl( PPh,) gives products such as (8) which can also be doped with SbF to give conducting polymers that have moleclar weights Mw = 119000 and 28 000 for R = Ph and Me respectively." RR -SiMeRSiMeR II 2 HCEC-Si-Si-C=CH II Me Me c=c (8) The degradation of polysilanes by UV light is becoming industrially important and new mechanistic workg9 shows that the process in solution involves reaction of (R2Si), to give silylenes R2Si and polysilyl radicals -SiR2-SiRe2.Addition of 18-crown-6 increases the rate of polymerization of MePrSiCl by sodium and also changes the molecular weight distribution from bimodal to monomodal with a molecular weight of -100OO0.90 Polymerization of 1-phenyl-7 8-disilabicyclo[2.2.2]octa-2 5-dienes by alkyllithium reagents provides a new route to polysilanes and also allows formation of block copolymers with methyl methacry- late." Treatment of 1,2,5,6-tetrasilacycloocta-3,7-diyneswith Bu"Li gives [Si(R)MeSi(R)MeC_C] polymers (R = Me Et or Ph) which also give highly conducting materials when doped with SbFs .92 A new method for the preparation of oligosilanes involves reaction of HSiC1 with silyltriflate in the presence of Et,N.For example reaction between HSiC1 and Me3SiOS02CF3or Me2Si(OS02CF3)2 affords Cl,SiSiMe and Me2Si(SiC13)2 respec- tively in yields of 72 and 62'/0.~~ Simple silyltriflates such as HSi(OS02CF3), [(CF302S0)2MeSi]2,and Ph9Si,(OS02CF3) that may be of use in such preparations can readily be made by cleavage of phenyl groups from the corresponding aryl 84 F. J. Feher D. A. Newman and J. F. Walzer J. Am. Chem. SOC.,1989 111 1741. 85 F. J. Feher and T. A. Budzichowski J. Organomet. Chem. 1989 373 153. 86 G.Kossmehl and A. Fluthwedel Chem. Ber. 1989 122 2413. 87 J. Ohshita D. Kanaya M. Ishikawa and T. Yamanaka J. Organomet. Chem. 1989 369 C18. 88 J. Ohshita K. Fuomori M. Ishikawa and T. Yamanaka Organometallics 1989 8 2084. 89 T. Karatsu R. D. Miller R. Sooriyakumaran and J. Michl J. Am. Chem. Soc. 1989 111 1140. 90 M. Fujino and H. Isaka J. Chem. SOC.,Chem. Commun. 1989,446. 91 K. Sakamoto K. Obata H. Hirata M. Nakajima and H. Sakurai J. Am. Chem. SOC. 1989 111 7641. 92 M. Ishikawa Y. Hasegawa T. Hatano A. Kunai and T. Yamanaka Organometallics 1989 8 2741. 93 W. Uhlig and A. Tzschach Z. Chem. 1989 29 335. Organometallic Chemistry-Part (iii) The Main-Group Elements 27 1 silanes by triflic acid.94 The palladium-catalysed reaction between aromatic acid chlorides and chlorodisilanes leads to decarbonylation and the formation of aryl chlorosilanes.This method proceeds in good yield is tolerant of various functional groups and should prove a useful route to numerous aromatic chlor~silanes.~~~~~ Triethylsilyl hydrotrioxide Et,SiOOOH prepared by addition of ozone to Et,SiH has been shown to be a powerful oxidizing agent reacting at -78 "C with alkenes to give 1,2-dioxetanes and oxidatively cleaved carbonyl produ~ts.~' Other potentially useful reagents are the new silicon pseudohalide Me,SiNCSe which reacts selectively with aldehydes but not ketones to give 0-trimethylsilylated cyanohydrin~,~~ (Me3Si0)2 which surprisingly reacts with 2-benzothiazolylalkyllithiums to give alkylbenzothiazoles incorporating a methyl group cleaved from one of the Me,Si moieties,99 Me,SiSSiMe3 which reacts with acylsilanes in the presence of CoC1 as catalyst to give the corresponding silylthioketones,"' and Et2PriSiC1 or Et2PriSiOS02CF3 which can be used to form silyl ethers of different stability to those of comparable Et,Si and Bu'Me2Si species.'o' The structures of two remarkably stable silanetriols (Me,Si),CSi(OH) and (Me3Si)3SiSi(OH)3,have both been found to consist of hydrogen-bonded hexameric cage units in the solid state.lo2 Kinetic evidence suggests that at high base concentra- tions the main process in the cleavage of RSiMe(OH) and RSi(OH) (R = m-ClC6H,CH2) is dissociation of the dianions RSiMe(O-)2 and R(OH)Si(O-) into Me(0-)Si=O (an acetate ion analogue) and the metasilicate ion HO(0-)Si=O re~pectively.''~ The X-ray crystal structures of hexacoordinate silicon compounds e.g.bis-[ 8-(dimethylamino)naphthyl]fluorosilaneand bis-[ 8-(dimethylamino)naphthyl]silane containing only one or no highly electronegative group have been determined and provide further evidence that such species may be intermediates in isomerization reacti~ns.''~~''~ Evidence for five-coordinate Si Sn and Pb compounds in which the metal is bonded to four carbons and intramolecularly coordinates to a nitrogen has also been reported.'06 Reaction between ICH2SiMe3 and alkoxide ions RO- does not give the expected Me3SiCH20R products but Me,SiOR and ROMe involving cleavage of a silicon-carbon bond probably via a five-coordinate silicon species.'" The first pentacoordinate silylsilicate (9) has been prepared and struc- turally characterized.'" The Si-Si bond length is 2.403 A and the geometry around the central silicon is trigonal-bipyramidal.94 W. Uhlig and A. Tzschach J. Organomet. Chem. 1989 378 C1. 9s J. D. Rich J. Am. Chem. SOC.,1989 111 5886. 96 J. D. Rich Organometallics 1989 8 2609. 97 G. H. Posner K. S. Webb W. M. Nelson T. Kishimoto and H. H. Seliger J. Org. Chem. 1989,54,3252. 98 K. Sukata J. Org. Chem. 1989 54 2015. 99 S. Florio and L. Troisi Tetrahedron Lett. 1989 30,3721. 100 A. Ricci A. Degl'Innocenti A. Capperucci and G. Reginato J. Org. Chem. 1989 54 19. 101 S. Florio and L. Troisi Tetrahedron Lett. 1989 30,6413. 102 S.S. Al-Juaid N. H. Buttrus R. I. Damja Y. Derouiche C. Eaborn P. B. Hitchcock and P. D. Lickiss J. Organomet. Chem. 1989 371 287. 103 J. Chmielecka J. Chojnowski W. A. Stanczyk and C. Eaborn J. Chem. SOC.,Perkin Trans. 2 1989 865. 104 C. Brelikre F. Cad R. J. P. Comu M. Poirier,G.Royo and J. Zwecker Organometallics 1989,8 1831. 10s C. Brelikre R. J. P. Corriu G. Royo and J. Zwecker Organometallics 1989 8 1834. 106 R. Koster G. Seidel B. Wrackmeyer K. Horchler and D. Schlosser Angew. Chem. Znt. Ed. Engl. 1989 28 918. 107 T. K. Chakraborty and G. V. Reddy J. Chem. SOC.,Chem. Commun. 1989 251. I08 M. Kira K. Sato C. Kabuto and H. Sakurai J. Am. Chem. SOC.,1989 111 3747. 272 P. D. Lickless F3C CF3 Ph3Si g% Et4N+ -rp 0 F3C CF3 A new relatively stable silene Ph2Si=C(SiMe3)2 can be prepared in solution by elimination of MX from (Me3Si)2(Ph2XSi)CM species (M = Li or Na X = F or Br) in a manner similar to that used for the Me,Si= analogue.'o9 Photolysis of acyl-silanes (Me,Si),RSiC(O)R' (R = Me But or Ph; R' = adamantyl etc.) gives silenes Me3SiRSi=C(OSiMe3)R' which rearrange further on photolysis to give various new silenes and cyclic dimeric products the nature of which depends on the size of R and R'.ll0 Treatment of acylsilanes (Me,Si),C(O)R (R = But or adamantyl) with Et3GeLi affords silaenolate species (Me,Si),Si=C(OLi)R for the first time."' The first example of a compound containing a 1-sila-3-azacyclobutane ring (10) has been prepared by addition of 2,6-dimethylphenylisocyanide to the silene (Me3Si)2Si=C(CloH15)OSiMe3 .lI2 On warming the hydrocarbon glass in which l-mesityl-2,3,4-tri-t-butyl-l-silacyclobutadiene is prepared an unusual dimerization involving a [1,5] sigmatropic shift occurs to give (ll).l13 A metal-bound silene is thought to be an intermediate in the reaction between Me3SiSi(Me2)CH=CH2 and Ni(PEt3)4 at 220°C,"4 and the formation of a metal-bound Si=C species is also implicated in the reaction between [Cp(C0)2Fe]MeSi(C1)CH=CH2 and Bu'Li which affords (12) apparently uia a head-to-tail silene dimeri~ation."~ 109 N.Wiberg M. Link and G. Fischer Chem. Ber. 1989 122 409. K. M. Baines A. G. Brook R. R. Ford P. D. Lickiss A. K. Saxena W. J. Chatterton J. F. Sawyer and B. A. Behnam Organometallics 1989 8 693.111 I. S. Biltueva D. A. Bravo-Zhivotovskii I. D. Kalikhman V. Yu. Vitkoskii S. G. Shevchenko N. S. Vyazankin and M. G. Voronkov J. Organomet. Chem. 1989,368 163. 112 A. G. Brook A. K. Saxena and J. F. Sawyer Organometallics 1989 8 850. 113 D. B. Puranik M. P. Johnson and M. J. Fink J. Chem. Soc. Chem Commun. 1989 706. 114 M. Ishikawa T. Ono Y. Saheki A. Minato and H. Okinoshima J. Organornet. Chem. 1989 363 C1. 115 N. Auner J. Grobe T. Schafer B. Krebs and M. Dartmann J. Organomet. Chem. 1989 363 7. Organometallic Chemistry-Part (iii) The Main-Group Elements 273 Reaction of Bu:Si=SiBu with the bulky BuiSiCN gives a 2,3-disila-l-azetine a [2 + 21 cycloaddition product while with BuiSiNCO a 3-aza-l-oxa-2,5-disilacyc-lopent-3-ene is formed."6 Addition of nitrosobenzene or nitrobenzene to (me~)~Si=Si(mes)~ gives the compounds (13) and (14) respectively both of which contain novel ring systems."' Ph Ph \ / N-0 0-N I.1 J\ Si(mes) (mes)2Si,0 Si(mes) (rne~)~Si-Photolysis of the trisilane (Me,Si),Si(mes) (adamantyl) gives the remarkably air- stable disilene (mes)AdSi=SiAd(mes) which has an Si=Si bond length of 2.138 A,118and disilenes with small substituents can be made in situ at a platinum centre to give some of the first T2-disilene complexes. The synthesis relies on the addition of a dihydrodisilane [(R2SiH)2(R = Pr' or Ph)] to either Pt(dppe)Cl or Pt(dppe)C,H . Unfortunately X-ray crystallographic data are not yet available for these interesting complexes.' i9 Photolysis of trisilane (15) affords (after rearrangement) silylene (16) which is remarkably stable and can be observed by UV spectroscopy (A,, 448 nm) in fluid 3-methylpentane solution at 200K.This silylene is the first to be observed under such conditions the bulky substituents presumably preventing further reaction.12' In contrast to the reaction of dimesitylsilylene with oxygen (which reportedly gave a silanone 0-oxide) the reaction of Me2% with O2in an argon matrix appears to give a dioxasilirane product,12' while insertion of O2 into the Si-Si bond of 1,l72,2-tetramesityl- 1 2-disilirane gives a cyclic peroxide species as a isolable solid which when treated with silica gel or Ph3P gives novel disiloxetane species.'21 Another transition-metal silylene complex (CO),FeSiMe,.HMPT has been struc- turally characterized the Si-Fe distance being found to be about 2.28 A.122 116 M.Weidenbruch B. Flintjer S. Pohl and W. Saak Angew. Chem. Int. Ed. Engl. 1989 28 95. 117 G. R. Gillette J. Maxka and R. West Angew. Chem. Int. Ed. Engl. 1989 28 54. 118 B. D. Shepherd D. R. Powell and R. West Organometallics 1989 8 2664. 119 E. K. Pharn and R. West J. Am. Chem. SOC.,1989 111 7667. 120 D. B. Puranik and M. J. Fink J. Am. Chem. SOC.,1989 111 5951. 121 A. Patyk W. Sander J. Gauss and D. Crerner Angew. Chem. Int. Ed. Engl. 1989 28 898. 122 C. Zybill D. L. Wilkinson C. Leis and G. Muller Angew. Chem. Int. Ed. Engl. 1989 28 203. 274 P. D. Lickless I i Si : hv -p 254 nrn The chemistry of the first silicon .rr-complex (~~-c~Me~)~Si has been explored further.'23 Different pathways seem to be followed in reactions with CS, C02,and PhNCS'24 and with Se or Te,'25 all of which give cyclic products.Reaction of a digermirane with dimethylacetylenedicarboxylate and acetylene in the presence of catalytic amounts of palladium catalyst gives ring expansion prod- ucts. However the stoichiometric reaction between the digermirane and Pd( PPh3)4 gives the palladadigermetane (17).'26 An unusual symmetrical twist-boat conforma- tion has been found in 2,2,5,5-tetramethyl-1,3-diselena-2-germacyclohexane. The barrier to interconversion of the two enantiotopic conformational isomers 34.4 kJ mol-' is surprisingly high and the reasons for this behaviour clearly require further study.12' Ar2GeAGeAr2 \/ Pd 1 PPh3 (17) Ar =2,6-Et2C,H For the first time several polycyclic oligogermanes have been reported.Reduction of (Bu~X,G~)~ (X =Br or Cl) with lithium naphthalenide affords octagermanes (18)'28and (19),12' respectively both of which have been fully structurally character- ized. The chloride can also be prepared by reduction of Bu'GeCl,. Reduction of another bulky halogenogermane (Me,Si),CHGeCl ,with lithium affords the first hexagermaprismane (2O).l3' Cyclopentadienyl complexes of Ge Sn and Pb continue to be of interest with various sandwich and half-sandwich complexes containing the 1,3-Bu:C5H3 ,131 123 P. Jutzi U. Holtmann D. Kanne C. Kriiger R. Blom R. Gleiter and I.Hyla-Kryspin Chem. Ber. 1989 122 1629. 124 P. Jutzi and A. Mohrke Angew. Chem. Int. Ed. Engl. 1989 28 762. 125 P. Jutzi A. hohrke A. Muller and H. Bogge Angew. Chem. Znt. Ed. Engl. 1989 28 1518. 126 T. Tsumuraya and W. Ando Organometallics 1989 8 2286. 127 S. Tomoda M. Shimoda M. Sanami y.Takeuchi and Y. Iataka J. Chem. SOC.,Chem. Commun. 1989 1304. 128 M. Weidenbruch F.-T. Grimm S. Pohl and W. Saak Angew. Chem. Int. Ed. Engl. 1989 28 198. 129 A. Sekiguchi H. Naito H. Nameki K. Ebata C. Kabuto and H. Sakurai J. Organomet. Chem. 1989 368,c1. 130 A. Sekiguchi C. Kabuto and H. Sakurai Angew. Chem. Znt. Ed. EngL 1989 28 55. 13 I P. Jutzi and R. Dickbreder 1. Organomet. Chem. 1989 373 301. Organometallic Chemistry-Part ( iii) The Main-Group Elements 275 R / RGe-R RGe -GeR R R-Ge-GeR /\ ~ I RGe GeR X (18) X = Br R = But (20) R = (Me,Si),CH (19) X = C1 R = But l,l'-(dimethylsilanediyl)bis-(2,3,4,5-tetramethyl-cy~lopenta-2,4-diene),~~~Me,-or C5133 ligands being prepared.The first germapyrazoline (21)has been prepared by addition of diazomethane to a Ge=C containing precursor. On heating or photolysis loss of N2 occurs to give a germirane which then decomposes to give (me~)~Ge:.'~~ Novel three- and four-membered rings e.g. in (22)and (23),containing Ge and S are formed on addition of germylenes to thio-ketones or -ketenes with subsequent o~idation.'~~,'~~ 0 II mes2Ge +&S -+ G~ MCPBA -@>O mes2 mes2 The electronic spectra of R,Ge (R = Me Et Ph etc.) species and their adducts with for example EtOH Bu3P Me2S and PhCl have been recorded in hydrocarbon matrices.The adducts show absorption bands at shorter wavelengths than the corresponding free germylene~.'~' The IR spectrum of matrix-isolated Me2Ge has 132 F. X. Kohl R. Dickbreder P. Jutzi G. Muller and B. Huber Chem. Ber. 1989 122 871. 133 P. Jutzi R. Dickbreder and H. Noth Chem Ber. 1989 122 865. 134 M. P. Egorov S. P. Kolesnikov 0. M. Mefedov and A. Krebs J. Organomet. Chem. 1989 375 CS. 135 T. Tsumuraya S. Sato and W. Ando Organometallics 1989 8 161. 136 W. Ando and T. Tsumuraya Organometallics 1989 8 1467. 137 W. Ando H. Itoh and T. Tsumuraya Organometallics 1989 8 2759. 276 P.D. Lickless also been recorded. 13' Reaction between stabilized diaminogermylene and diamino- stannylene precursors with a cyclic acetylene gives the first digerma- and distannacy- clobutene derivatives (24) re~pective1y.l~~ (24) M = Ge or Sn Photolysis of phenyl-substituted trigermanes e.g. (PhMe,Ge)*GeMe and (Me3Ge)2GePh2,occurs in a similar fashion to that of aryltrisilanes giving germy- lenes and digermenes which can be trapped by dienes.14' Reduction of (2,6- Pr;C6H3),GeCl2 (R2GeC1,) with lithium naphthalenide in DME gives digermene R,Ge=GeR which reacts further with excess reducing agent to give a vinyllithium equivalent R,Ge=GeRLi(DME) which should be a useful precursor to other digermene~.'~~ N20 or DMSO) Depending on the source of the oxygen (302 oxidation of digermenes R,Ge=GeR (R = 2,6-Et,C6H3 or 2,6-Pr&H,) gives 1,2- digermadioxetane digermoxirane and 1,3-cyclodigermoxane products respec-ti~e1y.l~~ Addition of thermally generated (mes),Ge=Ge(mes)* to paraformal-dehyde thiobenzophenone and phenylacetylene gives novel 1,2,3-oxa- and 1,2,3- thia-digermetanes and 1,2-digermetene products re~pective1y.l~~ The organometallic chemistry of tin is covered extensively in a new book,'44 the chemistry of tin cluster compounds has been re~iewed,'~' and a 'Tetrahedron Symposium in Print' covers organotin reagents in organic synthesis.'46 The trialkylstannane (PhMe2CCH2),SnH can be handled in air is soluble in organic solvents adds to activated olefins and is proposed as a new organotin reducing agent.14' A simple preparation of Me3SnH is achieved by reduction of Me,SnCl with LiAlH in triglyme at 60-68 "C in 81% yield.This convenient preparation may make Me,SnH a useful alternative to Me,SnCl Me3SnLi and Bu;SnH as a simple organotin reagent.14' The reaction between R,SnLi (R = Me or Bun) reagents with esters or thioesters provides a convenient route to various 138 J. Barrau D. L. Bean K. M. Welsh R. West and J. Michl Organometallics 1989 8 2606. 139 A. Krebs A. Jacobsen-Bauer E. Haupt M. Veith and V. Huch Angew. Chem. Znt. Ed. Engl. 1989 28,603. 140 M. Wakasa I. Yoneda and K. Mochida J. Organomet. Chem. 1989,366 C1. 141 J. Park S. A. Batcheller and S. Masamune J. Organomet. Chem. 1989 367 39. 142 S. Masamune S.A. Batcheller J. Park W. D. Davis 0. Yamashita Y. Ohta and Y. Kabe J. Am. Chem. SOC.,1989 111 1888. 143 W. Ando and T. Tsumuraya J. Chem. SOC.,Chern. Commun. 1989 770. 144 'Chemistry of Tin' ed. P. G. Harrison Blackie Glasgow and London 1989. 145 R. R. Holmes Acc. Chem. Rex 1989 22 190. 146 Tetrahedron 1989 45 pp. 909-1219. 147 A. B. Chopa A. E. Zfiiiiga and J. C. Podesta J. Chem. Res. (S) 1989 234. 148 B. H. Lipshutz and D. C. Reuter Tetrahedron Lett. 1989 30,4617. Organometallic Chemistry-Part (iii) The Main-Group Elements 277 potentially useful acylstannanes such as PhCOSnMe and C4H7COSnBu; in reason- able ~ie1ds.l~~ Reaction of [(2,4,6-Pr;C6H2)2SnBr]2 with Na2S-9H20 in air gives (25) and anaerobically gives (26) the first examples of such ring systems.In (25) the Sn-0-Sn and Sn-S-Sn bond angles are 101.7 and 80.6" re~pectively.'~' The four-membered ring compounds (BuiSnE) (E = S Se or Te) all have planar rings,151 while in (Me2SnTe)3 the six-membered ring adopts a twist-boat conformation. 152 b R2Sn'y'SnR2 R = 2,4,6-Pr;C6H (25) E = S E' = 0 (26) E = E' = S Partial hydrolysis of RSnC1 (R= Pr' or Bu') affords RSn(OH)C12-H20 species which in the solid state form dimeric units containing Sn202 rings. These units are hydrogen bonded to form chains which are further linked as 1a~ers.l~~ The use of bulky mesityl groups allows the monomeric four-coordinate tin hydroxide (mes),SnOH (Sn-0 bond length 1.999 A) and tin fluoride (mes),SnF (Sn-F bond length 1.96 A) and not polymeric species to be formed.'54 A series of seven bulky alkyl and aryl di- tri- and tetrastannanes have been investigated by X-ray crysta110graphy.l~~ As expected larger R groups increase Sn-Sn bond distances those in BukSn being 2.966(1) 8 long.The blue-violet solid 2,2,4,4,5,5-hexakis-(2,6-diethylphenyl)pentastanna[ 1.1. llpropellane has been found to have a distance of 3.367 8 between bridgehead tin atoms and no coupling between them in NMR spectra indicating that there is no bonding between the bridgehead atoms and that the compound has significant biradical ~haracter.'~~ An T2-coordination of R,SnH to a transition metal has been found in (v5-MeC5H4)-(CO),Mn(H)SnPh, prepared by photolysis of a mixture of ($-MeC5H,)Mn(CO) and Ph,SnH.X-Ray crystallography shows the Sn-H Mn-H and Sn-Mn bond lengths to be 2.16 1.37 and 2.6368, respectively with an Sn-Mn-H angle of 550 157 The crystal structure of a new diaryltin( 11) compound bis-[8-(dimethyl- amino)naphth- 1-yl- C N]tin( 11) shows distorted trigonal bipyramidal geometry at tin with nitrogen atoms of intramolecularly coordinated NMe groups in axial 149 A. Capperucci A. Degl'lnnocenti C. Faggi G. Reginato and A. Ricci J. Org. Chem. 1989 54 2966. 150 P. Brown M. F. Mahon and K. C. Molloy J. Chem. SOC.,Chem. Commun. 1989 1621. I51 H. Puff G. Bertram B. Ebeling M. Franken R. Gattermayer R. Hundt W. Schuh and R.Zimmer J. Organomet. Chem. 1989 379 235. 152 R. J. Batchelor F. W. B. Einstein and C. H. W.Jones Acta Crystallogr. Sect. C 1989 45 1813. 153 H. Puff and H. Reuter J. Organomet. Chem. 1989 364,57. 154 H. Reuter and H. Puff J. Organomet. Chem. 1989 379 223. H. Puff B. Breuer G. Gehrke-Brinkmann P. Kind H. Reuter W. Schuh W. Wald and G. Weidenbriick J. Organomet. Chem. 1989 363 265. IS6 L. R. Sita and R. D. Bickerstaff J. Am. Chem. SOC. 1989 111 6454. 157 U. Schubert E. Kunz B. Harkers J. Willnecker and J. Meyer J. Am. Chem. SOC.,1989 111 2572. P. D. Lickless position^.'^^ The reaction between Sn(AlCl,) and benzene affords the dimer (27) as the first bis(arene) complex of a Group IV element.'59 The eight-membered Sn,C1,Al2 ring has a chair conformation each pair of benzene rings are inclined to each other at about 101"and the Sn-ring centroid distances are very long (-3.2 A).Another tin-arene complex (28) is formed in the reaction between SnCl, AlC13 and Me&. It has an Sn-C&k6 distance of 2.45 A which is somewhat shorter than that found in complexes of tin with p-xylene and mesitylene.'60 The ability of 1,5,9-tristannadodecanes such as R,S(II(CH~),S~R,(CH,)~-I SnR,(CH,) (R= Me or Cl) to complex chloride ion has been studied.16' For R = C1 a single chloride ion can be complexed giving an anion in which there is a chloride bridge between two of the SnCl groups. For R= Me no significant complexation occurs. A series of bicyclic compounds (29; X = C1 or Br) can exist with either both halogens outside (an 'out-out' isomer) the macrocycle core (n = 6,7 or 8) or as a mixture of the 'out-in' isomer in which one halogen is outside and one inside (n= 10 or 12)."j2 Me \ C /+C \BPr X-Sn-(CH2) -Sn-X Me2Pb\ /c=c\ Me Pr' Triorganolead cations such as (30) can be stabilized by intramolecular coordina- tion to a CEC bond.'63 The Pb to CZEC carbon distances are 2.648 and 2.467A and the interaction may be viewed as like that of an intermediate in the addition reaction of a metal fragment to a triple bond.J. T. B. H. Jastrzebski P. A. van der Schaaf J. Boersrna G. von Koten D. Heijdenrijk K. Goubitz and D. J. A. de Ridder J. Organornet. Chern. 1989,367 55. 159 H. Schrnidbaur T. Probst B. Huber 0. Steigelrnann and G. Muller Organornetallics 1989 8 1567. 160 H. Schrnidbaur T. Probst 0.Steigelrnann and G.Muller 2. Naturforsch B 1989 44 1175. 161 K. Jurkschat H. G. Kuivila S. Liu and J. A. Zubieta Organornetallics 1989 8 2755. 162 M. T. Blanda J. H. Homer and M. Newcornb J. Org. Chern. 1989 54 4626. 163 B. Wrackrneyer K. Horchler and R. Boese Angew. Chern. Int. Ed. Engl. 1989 28 1500. Organometalfic Chemistry-Part (iii) The Main-Group Elements 279 The lead cationic species Me3PbLi can be prepared in THF solution at -78 "C by reaction between Me,PbBr and lithium. It rapidly decomposes at -20 "C but can be used at -78 "C to prepare for example Me,PbSiMe .164 Reaction between the carbaborane Na[ 2,3-( Me3Si),C2B4H5] with PbC1 affords the plumbacarbaborane closo-1-Pb-2,3-(Me3Si),-2,3-C2B4H4 in which the lead atom is q5-bonded to the C2B3 face with Pb-C distances of -2.6 5 Group V The new reagent (3,3-diisopropoxypropyl)triphenylarsonium ylide acts as a P-formyl vinyl anion equivalent and can be used to convert aldehydes into y-hydroxyenals in a three-step procedure,166 and a mixture of Bu;As and Zn has been shown to be a useful system to convert various aromatic aliphatic and heterocyclic aldehydes into alkenes in a one-pot rea~ti0n.l~~ A Wittig-type reaction is observed in the reaction between an aldehyde and BrCH2C02Me in the presence of Bu;As K2C03 and (Ph0)3P to give products of the type RCH=CHCO,Me.The novelty of this reaction lies in it being catalytic in Bu;As which is regenerated from the Bu;AsO formed in the reaction by the (PhO),P. This appears to be the first demonstration of such a catalytic Wittig-type reaction.16' In contrast to the hydrolysis of cyclo-(CH,),AsH [which affords cyclo-(CH,),As(O)OH] the hydrolysis of cyclo-(CH,),AsCl gives [cyclo-(CH,),AS(OH)~]CI.This can be considered as a cationic arsenic (v) diol or a dialkylarsenic acid in which the molecules are linked via intermolecular OH...Cl.-.HO- hydrogen bonds.169 Heating of cyclo-(AsR) (R = Me n = 5; R = Ph n = 6) with [q5-Me,C,M(CO),] (M = Mo or W) affords Me5C5M(C0),(q3- RAsAsAsR) complexes in which the RAsAsAsR acts as an isoelectronic and isolobal wallyl ligand; this is the first time that such a ligand not containing ligating carbon atoms has been found. The As-As bond lengths are -2.36 ,& with an As-As-As angle of -830.170 The asymmetric synthesis of optically active tertiary arsine (R)-(-)-EtMePhAs has been achieved via an iron complex containing the first resolved secondary arsine (31).17' 4- PF Me -Ai 4H I Ph Ph 164 B.Wrackmeyer and K. Horchler Z. Naturforsch. E 1989 44 1195. 165 N. S. Hosmane U. Siriwardane H. Zhu G. Zhang and J. A. Maguire Organometallics 1989 8 566. 166 P. Chabert J. B. Ousset and C. Mioskowski Tetrahedion Lett. 1989 30,179. 167 Y. Shen B. Yang and G. Yuan 1.Chem. Soc. Chem. Commun. 1989 144. I68 L. Shi W. Wang Y. Wang and Y.-Z. Huang J. Org. Chem. 1989 54 2027. 169 J. W. Pasterczyk A. M. Arrif and A. R. Barron J. Chem. Soc. Chem. Commun. 1989 829. 170 J. R. Harper M. E. Fountain and A. L. Rheingold Organometallics 1989 8 2316.171 G. Salem and S. G. Wild J. Organomet. Chem. 1989 370 33. 280 P. D. Lickless The X-ray crystal structures of Ar3As Ar2AsOAsAr2 and Ar2AsAsAr2 (Ar = C6F5)-the first tetraaryldiarsine to be so characterized- have been determined.'72 Annual reviews of the chemistry of antimony'73 and bismuth'74 for 1987 and a review of the use of organobismuth reagents in arylation reactions have been p~blished.'~~ Treatment of RSbBr2 compounds (R = Et Pr or Bu) with magnesium gives cyclic (RSb) and (RSb)5 products. Attempts to isolate the compounds by evaporation of the solvent lead to formation of polymeric (RSb) species. However [(mes)Sb],-C,H can be isolated and X-ray crystallography shows it to comprise Sb4...Sb4..- chains with the benzene ring bonded in an v6-fashion to one Sb of each rn01ecule.'~~ The first secondary stibane [(mes),SbH] to be structurally characterized is found to be surprisingly stable towards oxidation.X-Ray crystallography shows it to have a C-Sb-C angle of 101.7'. Treatment of (me~)~SbH with Bu"Li affords (mes),SbLi which when added to a mixture of CuCl and Me3P in THF gives [(mes),SbCu( PMe3)2]2-the first example of a late-transition-metal antimonide. The compound has a planar Sb2Cu2 four-membered ring with a Cu-Sb distance of 2.669 A new general method for the preparation of bismuthonium ylides (32) involves the treatment of Ph3Bi0 or Ph3BiC12 with sodium salts of 1,3-dicarbonyl compounds. Reaction of the ylides with sulphenes gives 1,3-0xathiole 3,3-dio~ides."~ Li+ BiPh R' (32) R-R' = CH,CMe2CH (33) R = CF R,R = Me Ph etc.To1 = p-MeC6H A series of pentaarylbismuth compounds Ar3AriBi have been prepared by treat- ment of Ar3BiX2 species with Ar'Li (X = F or C1; Ar = p-MeC6H4Ar' = C,F,; Ar = Ph Ar' = 2,6-F2CsH3 et~.).'~~ As for Ph5Bi the compounds have square- pyramidal geometry in the solid state. The first thermally stable hexacoordinate bismuthate complex (33) is prepared by treatment of a five-coordinate precursor with a dilithium reagent.18' 172 A. L. Rheingold D. L. Staley and M. E. Fountain J. Organomet. Chem. 1989 365 123. 173 L. D. Freedman and G. 0. Doak J. Organomet. Chem. 1989,360 263. 174 G. 0. Doak and L. D. Freedman J. Organomet. Chem. 1989 360,297. 17' J.-P.Finet Chem.Rev. 1989 89 1487. 176 M.AteS H. J. Breunig S. GulleG W. Offermann K. Haberle and M. Drager Chem. Ber. 1989 122 473. 177 A. H. Cowley R. A. Jones C. M. Nunn and D. L. Westmoreland Angew. Chem. Znt. Ed. Engl. 1989 28 1018. 178 T. Ogawa T. Murafuji and H. Suzuki J. Chem. Soc. Chem. Commun. 1989 1749. 179 A. Schmuck and K. Seppelt Chem. Ber. 1989 122 803. 180 K.-y. Akiba K. Ohdoi and Y. Yamamoto Tetrahedron Lett. 1989 30,953. Organornetallic Chemistry-Part (iii) The Main-Group Elements 28 1 6 Group VI The first selenoaldehyde (34) can be prepared according to the reaction shown in Scheme 2. It is an air-stable blue solid which isomerizes on melting to give the benzoselane (35).lg1 SeCN I H-$-SiMe3 A CH,CI t (34) Scheme 2 The reaction between aldehydes RCHO (R = Me Ph etc.)with (Me,Si),Se affords 1,3,5-triselenacyclohexanes(CHRSe) ,apparently via selenoaldehyde intermediates RCHSe.The cyclic selanes can be decomposed either thermally or with Lewis acid to regenerate the selenoaldehyde which can be trapped as a Diels-Alder adduct.Ig2 The formation of methyl 2H- 1-benzoselenete-2-carboxylateas a reactive inter- mediate on photolysis of 3-diazobenzo[ blselenophen-2(3 H)-one is implicated by the isolation of its dimer. This seems to be the first synthetic approach to the benzoselenete ring system.lg3 The new heterophane 2,l l-diselena[3.3](2,6)pyridinophane has been prepared in high yield and has been shown to interact with both Ni2+ and Cu2+ ions in a host-guest type complex.'84 The structure of 2,l l-diselena[3.3]orthocyclophanehas been shown to be anti rather than syn in both the solid and solution state.lg5 A new one-pot synthesis of bis(ethylenedise1eno)tetrathiafulvalene relies on the use of HMPA as solvent rather than the usual THF and gives yields of -50% of this compound which is of potential interest in the organic superconductor field.lg6 Functional species such as tetraformyltetraselenafulvalene have also been pre- pared.18' The Hammett constants a,,, and upfor PhTe PhSe Te- and Se- have been found to be (a,) 0.20 0.20 -0.57 and -0.59 respectively and (a,)0.29 0.22 -0.72 and -0.84 respectively by electrochemical reduction of various aryl chalcogenide species.lgg New selenium coronands such as 1,3,7,9-tetraselenacyclododecane and 1,3,7,9,13,15-hexaselenacyclooctadecaneand their derivatives have been fully 181 R.Okazaki N. Kumon and N. Inamoto J. Am. Chem. SOC.,1989 111 5949. 182 Y. Takikawa A. Uwano H. Watanabe M. Asanurna and K. Shimada Tetrahedron Lett. 1989,30,6047. 183 S. Yarnazaki K. Kohgami M. Odazaki S. Yarnaba and T. Arai J. Org. Che?. 1989,54 240. 184 S. Muralidharan M. Hojjatie M. Firestone and H. Freiser J. Org. Chem. 1989 54 393. 185 T. Okajima Z.-H. Wang and Y. Fukazawa Tetrahedron Lett. 1989 30 1551. 186 A. M. Kini B. D. Gates M. A. Beno and J. M. Williams J. Chem. SOC.,Chem. Commun. 1989 169. 187 M. Salk. A. Gorgues J.-M. Fabre K. Bechgaard M. Jubault and F. Texier J. Chem. SOC.,Chem. Commun.1989 1520. 188 R. hest and C. Degrand J. Chem. SOC.,Perkin Trans. 2 1989 607. 282 P. D. Lickless characterized and are shown to have different conformations to S and 0 analogues in the solid state.'89 The use of 1,4-dicyanonaphthalene as an electron acceptor enables the photo- chemical formation of the synthetically useful PhSe+ species from PhSeSePh for the first time.'" Oxidation of 1,5-diselenacyclooctane with two equivalents of NOPF gives a novel salt (36) that can oxidize 1,2-diphenylhydrazine to azobenzene and PhSH to PhSSPh.191 Bis( acyl diselenides) such as [PhC(O)Se] act as acylating reagents for such nucleophiles as R,NH Et,ONa PhSNa etc. under mild conditions and in good yield with both acyl groups 'being ~ti1ized.l~~ Similar bis( acyl) selenides [RC(O)],Se can be prepared in good yield from RC(0)Cl and Na,Se (R = Me Pr' But et~.).'~~ A versatile one-pot synthesis of unsymmetrical organoselenium compounds RSeR' [R = n-C6H13 PhCH2 PhC(0); R' = Pri PhC(O) EtOC(O) etc.] is achieved via sequential cleavage of Me,Si groups from (Me,Si),Se with Bu"Li and subsequent treatment with a suitable organic chloride or bromide.'94 A tetraalkyl Te'" compound Me,Te has been isolated for the first time as a yellow-orange pyrophoric liquid.The compound is prepared by reaction of TeC1 with 4,2 equivalents of MeLi at -78 "C. It is relatively thermally stable but decom- poses to give Me,Te after 4 h at 120 0C.195 The ditelluroethers RTe(CH,),TeR (R = Ph or Me) act as chelating ligands in Ptrl and Pd" complexes such as [Pd{PhTe(CH2),TePh)I2] and [Pt{MeTe(CH,),TeMe}Cl2].Both meso and (*) isomers can be formed.'96 The mechanism of the solvolysis of p-EtOC6H4TeC13 in for example a C&- MeOH mixture has been investigated. Such reactions give p-EtOC6H4Te(0)C1 and p-EtOC6H4Te(OMe),c1 as solid product^.'^' The X-ray photoelectron and NMR spectra of various tellurapyrans tel-lurapyranones and tellurapyrylium salts have been recorded for both Te" and Te'" compounds so that correlations between NMR chemical shift and binding energy could be in~estigated.'~~ 189 R. J. Batchelor F. W. B. Einstein I. D. Gay J.-H. Gu B. D. Johnston and B. M. Pinto J. Am. Chem. SOC.,1989 111 6582. 190 G. Pandey V. J. Rao and U. T. Bhalerao J. Chem. SOC.,Chem.Commun. 1989 416. 191 H. Fujihara R. Akaishi T. Erata and N. Furukawa J. Chem. SOC.,Chem. Commun. 1989 1789. Y.Nishiyama A. Katsuura Y. Okamoto and S. Hamanaka Chem. Lett. 1989 1825. 193 H. Kageyama H. Tsutsumi T. Murai and S. Kato Z. Naturforsch B 1989,44 1050. 194 M. Segi M. Kato T. Nakajima S. Suga and N. Sonoda Chem. Lett. 1989 1009. 19s R. W. Geddridge jun. D. C. Hams K. T. Higa and R. A. Nissan Organornetaffics,1989 8 2817. 196 T. Kemmitt W. Levason and M. Webster Inorg. Chem. 1989 28 692. 197 N. K. Adlington J. D. Miller and T. A. Tahir J. Chem. SOC.,Dalton Trans. 1989,457. 198 M. R. Detty W. C. Lenhart P. G. Gassman and M. R. Callstrom Organometaflics,1989 8 861. 19' Organometallic Chemistry-Part (iii) The Main-Group Elements 283 The hydrotelluration of acetylenes has been studied in detail.The addition of RTeH species (generated in situ) gives 1,2-substituted regioisomers exclusively with aromatic acetylenes but some 2,2-isomer is also produced on addition to aliphatic acetylenes. Use of HTe-ion allows divinyl tellurides to be made e.g. (PhCH=CH2)2Te.'99 Such vinyl and divinyl tellurium compounds can be used in the preparation of vinyllithium reagents.2oo The first stable alkyltelluryl halides have been prepared by utilizing the steric protection afforded by the bulky (Me3Si),C group. Thus treatment of [(Me3Si)&TeI2 with S02C12 Br2 or I2 affords (Me,Si),CTeX (X = C1 Br or I) in high yield. Treatment of the halides with RLi gives (Me,Si),CTeR (R = Me or Ph).201 A range of bis-(P-alkoxyalky1)ditellurideshave been made by treatment of an alkene with an aqueous mixture of Te02 an alcohol and HC1 with subsequent reduction using Na2S205.Treatment of the ditellurides with S02C12 gives crystalline (P-alkoxyalky1)tellurium trichlorides in good yield.202 Addition of activated elemental Te to Ph,P=CHPh gives the novel telluroaldehyde PhC(Te)H which can be trapped as its Diels-Alder adduct with 2,3-dimethyl- b~tadiene.~' A more general method for the preparation of telluroaldehydes and telluroketones uses (Me2Al),Te which converts RC(0)R' species such as benzal- dehyde and adamantanone into the corresponding RC(Te)R' species. Again the C=Te compounds could not be isolated but were trapped as Diels-Alder ad duct^.^'^ A corresponding reaction occurs to give selenoketones when (Me2Al)Se is used in place of (Me2Al)2Te.205 The need for volatile organotellurium compounds for MOCVD work has led to preparations of numerous new compounds.For example bis( alkyltel1uro)acetylenes RTeC-CTeR (R = Me or Et) can be prepared by treating HC-CLi-ethy- lenediamine with Te and then RI,206 and the reaction between Na2Te (made from Te and sodium naphthalenide) or LiTeMe and ally1 bromide affords (CH2=CHCH2),Te and CH2=CHCH2TeMe re~pectively.~'~ The reaction between PhCECH and Se and Te in three-phase systems comprising the metal PhCECH KOH H20 and an alkylammonium salt or selenium gives a 1,3-diselenole product but for tellurium distyryltellurium and the corresponding ditelluride are formed.208 In contrast to an earlier report the reaction between tellurium and PhCECH under strongly basic conditions has been reported to give 1 ,Cditellurafulvenes rather than a cyclic ditell~ride.~'~ Novel tellurodicarbonic acid esters [ROC( O)],Te (R = Me Pri PhCH2 etc.) can be prepared in reasonable yield by treating ROC(0)Cl compounds with Na2Te.These compounds seem to be more stable towards oxidation than diacyl tellurides 199 S. M. Barros M. J. Dabdoub V. M. B. Dabdoub and J. V. Comasseto Organometallics 1989 8 1661. 200 S. M. Barros J. V. Comasseto and J. Berriel Tetrahedron Lett. 1989 30 7353. 20 1 K. Giselbrecht B. Bildstein and F. Sladky Chem. Ber. 1989 122 1255. 202 L. Engman Organometallics 1989 8 1997. 203 G.Erker and R. Hock Angew. Chem. Int. Ed. Engl. 1989 28 179. 204 M. Segi T. Koyama Y. Takata T. Nakajima and S. Suga J. Am. Chem. SOC.,1989 111 8749. 205 M. Segi T. Koyama T. Nakajima S. Suga S. Murai and N. Sonoda Tetrahedron Lett. 1989,30,2095. 206 R. W. Geddridge jun. K. T. Kiga D. C. Harris R. A. Nissan and M. P. Nadler Organometallics 1989 8 2812. 207 K. T. Higa and D. C. Harris Organometallics 1989 8 1674. 208 V. A. Potapov S. V. Amosova and A. S. Kashik Tetrahedron Lett. 1989 30 613. 209 H. B. Singh and F. Wudl Tetrahedron Lett. 1989 30 441. 284 P. D. Lickless and attempted transesterification by for example treatment with an alcohol leads only to decomposition.210 A series of tellurocarboxylates RC(0)TeR’ (R = PhCH2 R’ = Et; R = 1-naphthyl R’ = Me) can be prepared as yellow to orange solids or liquids.The first step in the synthesis involves treatment of an acid chloride with Na2Te to give RC(O)TeNa which when treated with an alkyl or aryl iodide affords the RC(0)TeR’. This appears to be the first time that such compounds have been isolated.211 H. Suzuki and Y. Nishioka Bull. Chem. SOC.Jpn. 1989 62 2177. T. Kanda S. Nakaiida T. Murai and S. Kato Tetrahedron Lett. 1989 30 1829.