5 Carbon Silicon Germanium Tin and Lead By D.A. ARMITAGE Department of Chemistry King's College Strand London WCZR 2LS UK This review covers the literature for 1995. Carbon rings with 4n + 2 atoms favour a flattened structure. The cumulenes with a Dfn/2)hstructure have been found in a lower energy than the C(n,2)h structure of the cyclopolyyne for small C rings but the latter becomes more stable as n increases. Thus C, prefers D,, for CI4 D,h and C7h are nearly degenerate while C18 prefers a flattened circular polyyne c9h.I In an attempt to prepare the c180 fullerenyne comprising an icosahedral arrangement of cymantrene ([Mn(CO),(cp)]) residues bridged by 30 butadiynyl units [MnC,(CO),] 12-[C~C-CZC],~,a series of mono- and bis-(trimethylsilylethynyl) cymantrenes have been prepared.Desilylation and Hay coupling leads to oligomeric species up to the heptamer but they are unstable. Calculations have supported a tetracapped tetrahedron with a Tdstructure for the Ti,C, cluster. For the Til,C ,cluster a cube-like arrangement with Ti at the corners and C in the middle (face-centred cubic) is favoured. In the mass spectrometer the gas-phase reactions of V,,C, and V,,C, show sequential addition of eight moles + + of water to give hydrated hydroxides while eight moles of MeCN also adds sequentially. The Nb,C,+ cluster oxidizes to Nb,C,+ and reacts with water to give Nb4C40H+ while a range of NbC,' (n = 15-50) ion clusters occur as monocyclic rings (n < 22) and bicyclic rings graphitic sheets and metallof~llerenes.~ Heating erbium triiodide with erbium metal in the presence of carbon and NaN gives the carbide [Er14(C2)2(N)2]124 in which the tetrameric cation clusters comprise interconnected octahedra and tetrahedra filled with C and N respectively.The C-C bond distances are 144 ~m.~ The structure of tris(piperidino)cyclopropenium perchlor-ate shows short C-C distances of 137-139pm and C-N bonds of 133 pm supporting delocalization. With the bis(amino)chloro derivative [C,(NPr',),Cl] +,however two of the C-C bonds are significantly shorter (133pm) and one longer (143pm). The exocyclic C-N bonds are also shorter (127 and 130 pm).6 The reaction of osmocene and mercury(I1) acetate in I 1-dichloroethane gives the deca(acetoxymercurio) derivative which with CuX (X = C1 Br) and KI gives [Os($-C,X,),].The structure of the decachloro derivative shows the rings eclipsed and is isomorphous with the ruthenium analogue with the 0s-C bonds being very similar in length to the Ru-C bonds of the ruthenium deri~ative.~ + The sequential bond dissociation energies of [Cu(CO),] + and [Ag(CO),] (x = 1-4) increase up to x = 2 then decrease. A comparison with the isoelectronic [Ni(CO),] and [Co(CO),] -provides evidence for the increasing importance of n-back bonding as 53 D.A. Armitage electron density at the metal increases.8 Reducing [UCl(C,Me,H),] followed by carbonylation gives the first isolable carbonyl of an actinide [U(CO)(C,Me,H),]. The low carbonyl stretching frequency at 1900cm-'and short U-CO bond suggests strong back b~nding.~ The first metaloxyketene complexes (1)result through 'double insertion' of carbon monoxide into thorium-silicon bonds.Ketene absorption bands at 2044 and 1244cm-' for the pink complexes support the structure with the ketene angle 174" (Scheme l)." I R3 = (SiMe3)3 or Bu'Ph2 SiR3 lC0 CI Scheme 1 Carbon suboxide does not hydrolyse as readily as ketene in neutral and acid catalysed conditions by three to four orders of magnitude in support of ab initio calculations providing some support for its detection recently in the water-ice of comet Halley.' ' The calculated electronic spectra of polythiene suggest a polytrithiapentalene structure comprising a central carbon chain with sulfur atoms bonding to each carbon and to each other.This structure (2) is more stable than the polythioketone structure (3).' Carbon disulfide irradiated at 313 nm gives a polymeric solid of relative density 1.92 (liquid CS, 1.26) and vibrational data suggest trithiocarbonate groups with extensive S-S cross linking.' Carbon Silicon Germanium Tin and Lead Treating C,S,O (4) with base then [NEt,]Br gives the salt [NEt,],[C,S,] (5) with the planar anion showing extensive n delocalization. It readily complexes with both Ni2+ and Cu2 + to give semiconductors.14 A range of 2-thioxo-1,3-dithiole-4,5-dithiolates of Cu" have been made while [C,S,Se]2 -gives [Re,(C,S,Se),12 -which shows conductivity and has two dithiolate groups half bridging the Re-Re bond and the other three chelating the Re atoms (6) two on one and one on an~ther.'~ Oxidizing Ph,CSH with 4-MeC6H4SO2NSC1 in CS gives the perthiocarbonate Ph,CSSC(S)SCPh,*CS,.The structure shows the CS group to be planar and the S-S bond 201.4 pm.16 Treating Na,[PdCl,] and Na,S with [MeN(C,H,),NMe]I in MeOH at 110 "C gives the [Pd6(c2S6)(s,)6l6- cluster. The centrosymmetric hexa- thioorthooxalate anion c2s66-provides the central group and Pd atoms bridge pairs of sulfur atoms of this anion while S,,-anions bridge pairs of Pd atoms. The carbon atoms of the orthooxalate group are thought to result through demethylation of the amino cation. At 80 "C with PdCl, the [Pd6(C2S,)(S,),(S,),]6- anion res~1ts.l~ Photolysing the acylsilane (7) gives two geometric silene isomers which give PhCECH adducts at 90 "C and isomeric MeOH adducts at 100"C [equation (l)].Extensive heating in an attempt to eliminate (SiMe,),O and form the silyne results in extrusion and formation of (8) which adds PhCGCH and MeOH more readily [equation (2)].18 (7) (ratio 2 :1) R = adamantyl Me R Me Si \si-cP 120% si=c: 3 2,4,6-Pi3H2$ 'R 5d 2.4,6-Pi3H2$ SiMe2(OSiMe3) The ruthenium complex (9) which results from [RuCl(cp*){ P(C6Hl 1)3)] and Ph,C=C(Li)(SiHMe,) supports 1-silaallene co-ordination with the Si-C bond of the silaallene chain 180.5 pm shorter than the two terminal Si-C bonds of 186 and 188 pm and a Si-C-C angle of 128.9".19 D.A. Armitage The recent synthesis of [R~H(cp*)(q~-Me,C,SiSi(SiMe,)~)1 '[BPh,] -represents the preparation of the first $-silole complex.A structure determination indicated a planar structure for the silole ring and delocalization. This is also supported by the $-co-ordination of Li'in Li+ [Si(CH),H] -which increases delocalization and aromaticity relative to the parent anion. It shows 80% of the stabilization energy of Li+[C5H5]- but only 55% if not complexed vsto Li.,' Reducing 1,1-dichloro-2,3,4,5-tetraphenyl-l-silacyclopentadiene with lithium gives the q',q5-dilithiosilole solvated with thf three molecules for ql-Li and two for qs-Li. The Si-C bonds (184 and 185pm) are shorter than single bonds and the Si atom projects just 11 pm out of the plane.,' The germacyclopentadienide anion results from the deprotonation of the substituted germacyclopentadiene with base using either KN(SiMe3),-18-crown-6 or LiBu"-12-crown-4.The structure of the latter derivative (10)shows considerable pyramidalization at Ge with the angle between the GeC plane and Si being 100.1". Also the Ge-C bond length appears a little longer (196 and 201 pm) than those in the parent germane (194.4 and 194.8pm) [equation (3)]. Calculations support less aromaticity in the Ge derivative than in the Si one. This contrasts with the Ru derivative where the Ge-C bonds are 190.0 and 189.9pm.22 . 1 #H . .-I LiBu" 12-crown-A (3) .-.-... . . 'Si(SiMe& 'Si(SiMe3) The two salts [K(C6H6)]+[K{C(SiMe3)2(SiMe2Ph))2]-and [K(OSiMe,),] +-[K(C(SiMe,),[SiMe,(HC=CH,)]),] -result from the trisilylmethane and KMe the structure of the former indicating a Ph-K+-C6H6 sandwich with the potassium of the anion interacting strongly with the tertiary carbon atoms of two trisilylmethyl groups and with six methyl groups of separate silyl groups.23 Calculations suggest that the silylium cations give a 6(29Si)shift in the gas phase of 400 ppm and in non-co-ordinating solvents of 370-400ppm.Values less than this result for solvents with increasing co-ordinating ability. It has been suggested that carbocations disperse the positive charge more effectively so interact less effectively with the solvent.24 In the gas phase it is suggested that [SiR,-arene] complexes exist + as a Q complex although a .n one is not ruled Adding silyl enol ethers to a-asymmetric aldehydes using the supersilylating agent [SIR,] [B(O,SCF,),] as Carbon Silicon Germanium Tin and Lead catalyst indicates a level of Cram-type selectivity that correlates with the steric bulk of the silyl group with the triisopropylsilyl enol ether resulting in unprecedented 1,2-asymmetric induction [equation (4)].26 (97%)Cram (1%) antKram Gaseous SiMe,' interacts with the arylgermanes GeMe,(C,H,X) (X = H Me) to give the arylsilane and extrude the germyl cation.,' The trifluoromethanesulfonates (triflates) [GeMe,][B(O,SCF,),] and [SnEt,][B(O,SCF,),] hydrolyse to give the protonated bis(germy1)- and bis(stanny1)-oxonium salts.The structures indicate that the M-0 bond lengths increase 13 and 16pm respectively from those in (Ph,M),O (M =Ge Sn) with pronounced germylium and stannylium character and with tetrahedral flattening.28 With [SiMe,][B(O,SCF,),] bis[2-(dimethylaminomethyl)phenyl]silane and [(2- dimethylaminomethyl)phenyl]phenylsilane give the amino-co-ordinated silyl triflate.The former exists with a five-co-ordinate isolated cation but that of the latter is a very tight ion pair with the triflate group occupying one axial position around the trigonal-bipyramidal silicon.29 The reaction of !,2-dimethyl-1,2-disila-closo-dodecaborane( 12)Me2Si,Bl,Hl with alkali and then [NMe,]Cl gives [NMe,]+[MeSiB,,H,,]- in which one silicon atom has been removed from the Si,B icosahedral cage. 1,2-Dicarba-closo-dodecaborane( 12) alsc loses boron under strongly basic conditions. It has C symmetry with a protonated ollide-like structure possessing an open B,SiMe ring with two bridging hydrogen atoms.This is supported by the "B NMR spectrum which shows six signals in the ratio 1:2 2 2 2 1. The Si-B bonds are in the range 203.6-206.9 pm.,' The highly hindered disilene R(mes)Si=Si(mes)R {R = C6H,[CH(SiMe,),],-2,4,6) results from the reductive coupling of the dibromide with lithium naphthalenide. The (E) and (2)isomers show a remarkable pyramidalization at silicon and long Si=Si double bonds of 222.8 and 219.5 pm respectively. Both dissociate to the silylene at 70 "C and are air stable but eventually give the 1,3-dioxa-2,4-disiletane after 40d.,l The unsymmetrical disilene (rnes),Si=Si(C,H,Pr',-2,4,6) with rn-chloroperbenzoic acid gives the oxadisilirane while 0 gives the 1,3-dioxa-2,4-disiletane.With (mes),Si=Si(mes) and stilbene oxide the 3-oxa-1,2-disilacyclopropaneis formed together with the 2,4-dioxa- 1,3-disilacyclohexane and cyclodisiloxane.32 Treatment of (mes)(Bu')Si=Si(Bu')(mes) with sulfur gives a mixture of episulfide isomers.33 The disilirane (11) reacts with the dimetallofullerenes La,@C,, La@C8 and Sc,@C, to give the disi!acyclopentane derivative through addition to a C-C bond of the fullerene [equation (5)]. The gadolinium derivative Ga@C, reacts similarly and its ionization potential (6.25 eV) is similar to that of the lanthanum compound and is more reactive than C, which has a higher ionization potential (6.96 eV)., Cyclotetra- silanes and -germanes both add photolytically to c6 to give stable 1 1 adducts [( 12) and (1 3)] which result through rearrangement of the tetrasilane or tetragermane unit [Equation (6)].Photolysing [SiBu',] gives Si,(H)Bu' through disilene formation which dimerizes with loss of isobutene. The four-membered ring is slightly folded with two very long Si-Si bonds of253.8 pm. This ring also results from SiCl,Bu' and The highly D.A. Armitage branched decasilane (Me,Si),SiSiMe,SiMe,Si(SiMe,) results as crystals from Li(thf),Si(SiMe,) and shows Si-Si bonds of 234-237 pm while photolysis with CCl leads to cleavage of the central Si-Si bond.37 Condensing MM’Bu‘ (M = Si M’ = Na; M = Ge M’ = Li) with GeCl,*dioxane in thf gives the novel cyclotrigermene ring (14) with an isosceles structure with Ge=Ge 223.9pm7 some 28pm shorter than the other two ring bonds.The exocyclic Ge-Si bonds are 244.8 (Si-Ge=Ge) and 262.9 pm (Si-Ge-Ge much greater hindrance). It does not react with EtOH or CH,N but is oxidized by tcne at 100°C to Si(H)Bu‘ and But3 SiS iB u‘,. 4,8-Dihalogenooctakis( 1,1,2- trimethylpropyl)tetracyclo[3.3.O.O2~7.03~6]octasilanes (15)(X=Cl Br I) can be reductively dehalogenated with sodium to give red crystals of the octasilacubane together with the colourless dihydride (15) (X = H) with Si-Si 234.2-246.1 pm.,’ A higher isotactic polysilane results on reducing dichloro(methylpheny1)silanewith graphite-potassium C8K rather than an alkali metal. The molecular weight ap- proaches 100 OO0.40 The first reported tetraaryldistannene results from SnC1 and the Grignard reagent Carbon Silicon Germanium Tin and Lead 2-Bu'-4,5,6-Me3C,HMgBr.It is the monomeric stannylene in solution but dimerizes on crystallization with a long Sn-Sn bond of 291.0pmY a trans bent structure and fold angles of 21.4 and 64.4".,' The barium europium silicide Ba,Eu,Si comprises infinite chains of C3.3.3)baralene units comprising Si ,units (16) with elongated Si-Si bonds (241-244pm).* The nido lead cluster completes the series Pbg4- and is formed as a K+(K(cryptand- 222)') derivative with C, symmetry in the presence of a stoichiometric deficiency of cryptand 222. An excess of the cryptand gives Pb,[K(cryptand 222)] with a C, structure.43 Heating lead dioxide and potassium gives the basic hydroxide K,,Pb,O,(OH) which contains Pb,4- tetrahedra (Pb-Pb 310-31 1pm) which are also present in K4Pb4.44 The germylene :Ge[N(SiMe,),] displaces CO from the oxalate complex [Pt(C,O,)(PEt,),] in refluxing benzene to give the metal germylene derivative with planar geometry at Pt and Ge and a short Pt-Ge bond.45 With :Ge[CH(SiMe,),J addition to ethylene gives the unstable germirane which adds further germylene to give the 1,2-digerma~yclobutane.~~ Reducing this germylene and the analogous stannylene with sodium gives the radical anions the ESR spectra supportinglittle s character with the n radical^.^' The stannylene :Sn(C6H,Bu',-2,4,6) rearranges in solution to reduce crowding and gives :Sn(C,H,B~',-2,4,6)(~~,~~e,~~~~Bu~,-3,~).This reacts with [W(CO),(thf)] to give the Sn=W complex with trigonal-planar tin.With selenium the Sn,Se ring results.48 Treating :Pb[N(SiMe,),j' with KSi(SiMe,) gives black crystals of :Pb[Si(Si- Me,),],. The structure shows Pb-Si bonds of 270 pm and a SiPbSi angle of 114". The tin analogue can be prepared similarly but crystallizes as the distannene with a trans bent conformation and a Sn-Sn bond of 282pm in the single bond range.49 The stannocenes :Sn(C,H,Pr',-1,2,4) and :Sn(C,HPri4-1,2,3,4) result from the cyclopentadienylpotassium derivatives and SnCl in thf. The former is an air-sensitive oil and the latter an air-stable solid possessing a bent metallocene geometry like the calcium derivative." The lead derivatives :Pb(C,H,Bu',-1,2,4) (17) :Pb(C,HPr',-1,2,3,4) and Pb(C,Pr',) can be similarly prepared from the lithium cyclopentadienide while (17) also results remarkably from Pbg4- and [BiC1(C,H,Bu'3-1,2,4)2].51 With [Pb(cp),] and [Li(cp)] in 12-crown-4 a mixture of anionic sandwich complexes result in the formation of [Pb,(~p),]-[Pb~(cp)~]- [Li(12-crown-4)J2+.The polydecker sandwiches in the anions comprise Pb atoms trigonally bonded to three cp residues. By way of contrast [Sn(cp),] and [Li(cp)] give a paddle-wheel anion [Sn(cp),] -[Li(l2- crown4),] .52 + The first monoorganolead(I1) derivative [{Pb(p-Cl)[C(SiMe,Ph),]},] results from [Li(thf),{C(SiMe,Ph),}] and PbC1 as a yellow-orange solid with a centrosymmetric molecule with chloride bridges of 272.9 and 296.2pm and a stereochemically active lone pair., The Si-H addition to transition-metal complexes has long been known and that of trichlorosilane to [Cr($-arene)(CO),] occurs photolytically to give the Cr'" derivative (18) [equation (7)].There is no evidence to support either q2-HSiC1 or q2-H,bonding. Codepositing iron atoms and an excess of arene followed by addition of HSiCl gives the [Fe($-arene)(H),(SiCl,),] with J(29Si-1H) coupling constants of 15 Hz compared with 370 Hz for HSiCl, and supporting a Fe" complex with no q2-co-ordination.54 hv [Cr(q6-arene)(CO),] HSICI,-[Cr($-arene)(C0)2(SiC1&] + [Cr(q6-arene)H2(SiCI&] (7) (18) D.A. Armitage Trifluorosilane reacts similarly to give the first trifluorosilyl hydrido transition- metal complex [Fe(rf-C H Me)(H),(SiF,),] with the 'H NMR spectrum showing a septet with ,J(H-F) 9.2 &z.'~ The first transition-metal complex with silane SiH bonded q2 results from [Mo(CO)(R2PC2H,PR2),] (R = Ph Bu') and SiH,.The q2 bonding is supported by J(Si-H) 50 and 31 Hz and the structure of the Bu' derivative while in solution both the Bu' and Et derivatives show an equilibrium in which the q2 species and the seven-co-ordinate silyl hydride derivative is present [equation (8)].56 I SiH3 \SiH 0SiH2 Reaction of [{RuH,(cp*)),] with SiH2But2 leads to the three-membered Ru,Si ring in which the Si-H bonds act predominantly as an v2-ligand to the metal since J(Si-H) is 75 Hz. While an excess of SiH,Bu' does not react because of size less hindered silanes give a second bridge and q2 bonding from each Si-H bond.57 1,2-Disilylbenzene reacts with [Pt(PEt,),] at 80°C to give the first PtIvSi,P2 species (19) with octahedrally arranged substituents and cis phosphines.It reacts with more [Pt(PEt,)J to give the mixed-valence Pt"-Pt"' derivative (20) [equation (9)].58 Heating silicon diimide with alkaline-earth metals at about 1600 "C gives the nitrido silicates M2Si5N8 (M = Ca Sr Ba) in which the anion comprises a three-dimensional lattice of interconnected SIN tetrahedra in which the nitrogen atoms interact with either two or three silicon atoms in equal proportions. Lanthanide metals react similarly to give both LnSi,N and Ln,Si,N the SIN tetrahedra giving a zeolite-like lattice." Two tris(amin0)silanes RSi(NH,) have been prepared from the hindered trichlor- ides RSiCl (R = 2,6-Pri2C6H,NSiMe or 2,4,6-Bu',C6H20) using ammonia.While both have Si-N bond lengths in the range 169-172pm the NSiN angles vary from 101 to 123°.60 The tris(ptolysily1)amine is planar with Si-N bond lengths 172.8-1 73.6 ~m.~' 1,4,7,10-Tetraazacyclododecanereacts with MeSiC1 in the presence of NEtPr' to precipitate two moles of the base HC1 and gives the five-co-ordinate salt (21) which with an excess of LiBu" gives (22) which can be alkylated stepwise to give both mono- and 1,7-di-substituted macrocycles on hydrolysis [equation ( The compound [Si(NHSiMe,Bu'>,F(Ph)] reacts with LiBu' to give Carbon Silicon,Germanium Tin and Lead [Si(NLiSiMe,Bu'),F(Ph)]. Lithium fluoride loss in the presence of thf gives the silaamidide which is isolated as the cyclodisilazane anion (23) m.p.290°C. The endocyclic bonds (171-177pm) are much longer than the exocyclic ones (165.0 and 165.6pm) and the Si,N ring is not planar [equation (ll)].63 -+ I - CI- 3LiBu" (r) R'x __F (ir)R"X; (iii)H30+ 1- The amido germanates K,[GeO,NH,] and K,[GeO,NH,].K[NH,] result from GeO and KNH in supercritical ammonia at 450 "C in high-pressure autoclaves for days. The former contains tetrahedral GeO,NH,,- anions which are connected in chains by N-H.. * 0 bridges (218-240pm) while the latter contains GeO,NH,,- and NH,-ions with N-H...N hydrogen bonds (241-261 The hindered aminogermane (mes),Ge(Br)-NH(C6H,F,-2,4,6) on lithiation and heating eliminates LiBr to give the cyclodigermazane and the germaimine which adds chloroform across the Ge=N double bond and the nitrone (24) to give the five- membered heterocycle (25) (Scheme 2).65 R IN'CHPh -phCH=N(O)BU' (2-\O.~~~t LiBu" (mes)2Ge(Br)-NHR (me~)~Ge=NFi ycct3 (25) R = CeH2F3-2,4,6 Scheme 2 Condensing Sn(NMe,) with primary amines RNH provides a convenient route to imidotin(1r) tetramers [Sn(NR)] with cubane-like structures.66 The triorganotin fluoride hydrates [N(CH,CH,CH,),]SnF*H,O and [MeN(CH,CH,CH,),]-SnF(Me).H,O result from exchange of an Sn-Me group with SnFPr",.The former is a tetramer with intermolecular Sn -F interactions and hydrogen bonding and is the first intermolecular six-co-ordinate triorganotin fluoride. The metallotranes SnXN(CH,CH,CH,) (X = C1 Br I) show Sn.*.N interactions of about 238~rn.~' The first lanthanide tris(phosphid0) complexes [M(thf),{P(SiMe,),),] (M = Tm Nd) show trigonal-pyramidal co-ordination with the phosphido groups equatorial.68 62 D.A.Armitage With P(SiMe,), [Mo(CO),(cp)InCl,] gives the tetrameric cluster [{ Mo(CO),(cp)),In,(P(SiMe,)),] with a heterocubane-like In,P structure and Si-P bonds of 223.5 to 225.4~m.~' The first structurally characterized Si-P and Si-As multiple bonds (26) result from [SiF,Bu'(C6H,Pr',-2,4,6)] on reaction with [Li(EH,)(dme)] (E = P As) (Scheme 3). The disilaphosphene shows silicon-phosphorus bonds of 206.2 and 225.5 pm and the arsene analogue has silicon-arsenic bonds of 216.4 and 236.3 pm. The tellurium adduct of the arsene has Si-As 235.4 (endocyclic) and 239.6pm (exocyclic) and Si-Te 249.1 E = PIAS;R = C~H2Pj3-2~4~6 (26) E=As Te I Scheme 3 A range of thermally stable phosphine- and arsine-substituted carbene analogues result from the silyl-phosphides and -arsenides with Ge Sn or Pb dihalides and are either green or yellow-brown [equation (1211.Calculations indicate the carbene to be increasingly preferred to the double-bonded isomer as the atomic weight of M increases [equation (1 3)]. Reaction of the disilazane derivatives M[N(SiMe,),] (M = Ca Sr) with AsH(SiMe,) gives the alkaline-earth arsenides solvated with four moles of thf. The structures have octahedral co-ordination with trans arsenide ligands. The As-M-As unit is almost linear but in the Sr case one arsenic is trigonal planar and the other pyramidal.72 Condensing (2,4,6-Bu',C,H2)COC1 with Li[Sb(SiMe,),(dme)] gives the acylstibine which isomerizes through silyl migration then loses Si,Me6 to give the siloxy- substituted 2,3-distibabutadiene (27) [equation (14)].' Condensing SnCl,Me with K,[Bu'P(PBu'),PBu'] or K2[Bu'PPBuL] gives the SnP and Sn(P,),Sn rings the latter with a boat conformation showing Sn-P bonds 250-253 pm.74 The first accurate silyl cyanate structure has been determined for (Me,Si),(PhMe,Si)CSiMe,OCN.The Si-0 bond of 173.8pm is long and the SiOC bond angle is 126.7" with NCO almost linear (176.5"). This contrasts with the isocyanate (PhMe,Si),CSiMe,NCO in which Si-N is 173.9 pm and SiNC and NCO 155.7 and 175.9".75 While [Si(thf),](cat) and Li,[Si(cat),(dme),].O.Sdme show octahedral co-ordina- tion at Si the former with trans thf ligands the ethane-1,2-diol derivative [NaSi(C,H,0,),(C,H502)] shows one ligand monodentate and Si five-co-ordinate.The unbound OH group hydrogen bonds to adjacent oxygen atoms to give a tetrameric unit. Germanium is similarly five-co-ordinate in the complex Carbon Silicon Germanium Tin and Lead 63 R3Si\ MX2 ELi(thf)2 -[M{E(SiR'3)SiR3}2] (12) R;Si' E = P M = Ge Sn Pb; E = As M = Sn H H\ ,M=P\ H2P H R -Si,M+ RC(0)Sb(SiMe3)2 -RC(OSiMe3)= Sb(SiMe3) -(Me3Si)OC.r (14) Sb-Sb\\ R = C6H2BUt3-2,4,6 ,C(OSiMe3) R Na[Ge(OH)(C,H ,02),].3MeOH formed from GeO, pinacol and MeOH. The equatorial Ge-OH bond is shorter than the other two equatorial Ge-0 bonds.76 Oxidizing [(cp*)(OC),(Me3P)MSiH3] (M = Mo W) with dimethyldioxirane gives the metallosilanetriol which condenses with Me,Si(H)Cl to give branched siloxanes functionally substituted by Si-H.The silane diol [(C~*)(OC),(M~,P)MOS~M~(OH)~] crystallizes as a centrosymmetric hydrogen-bonded dimer the six-membered Si,O ring having a chair conformation with 0 -* 0 distances of 284 pm.77 The hindered germylene :Ge(C,H,Pri,-2,4,6)(C6H2[CH(SiMe3)2]3-2,4,6} can be oxidized to the germanone with (PhCH,),N+O. It adds to mesitonitrile oxide and slowly decomposes in solution to give isomeric intramolecular cycloaddition products [equation (15)].78 O(SiMe3) I HC(SiMe3) Both Sn" and Pb" form hydroxide clusters with [Sn3(OH),][NO3] possessing a six-membered ring structure (28) with the nitrate groups completing the SnO octahedra.With [Pb,(OH),][NO,] the four lead atoms are arranged in a tetrahedron with the OH groups bridging faces.79 With [Sn(OBu'),] and [Sn(OAc),] in refluxing toluene the hexagonal tub-like derivative [Sn,O,(OBU'),(O,CMe),] results. In pyridine however the exchange products [S~(OBU'),(OAC),-~] (x = 1,2,3) result. Using [Pb(OAc),] gives [PbSn,(p3- O)(OBu'),(OAc),] in toluene with structure (29) showing SnlV and Pb". In pyridine only [Sn(OBu'),(OAc)(py)] and [Pb(OAc),(OBu')] result. Transalcoholysis of [Sn(OBu'),] with an excess of Bu'OH gives [(Sn(OBui),(HOBui)},] quantitatively. D.A. Armitage H 12+ The ecige-bridged bioctahedral Sn unit is centrosymmetric and comprises a pair of intramolecular hydrogen bridges between apical co-ordinated alcohol and apical a1 koxide.meso-Oxolane-3,4-diolate gives a monohydrate with Pb" which is a one-dimensional polymer with Pb,O bridges formed from the diolate groups with water also co-ordinating to Pb".81 A structure determination of a diastereomer of AgLa,GeS shows a chain of AgS units co-ordinating to La in La,GeS cubane-like sub-units interconnected through Ge-S bonds.82 Heating freshly precipitated GeS and NEt,+HCO -with copper(I1) acetate gives crystals of [NEt,][CuGe,S,] comprising Ge,SIo4- clusters.83 With [PPh,][SnCl,] Na,S gives the Sn" derivative Sn(S,),,-with an octahedral structure while (Sn,S,)(NHMe,) consists of sheets with 24-membered rings compris- ing six Sn,S units interconnected through sulfide bridges at each tin atom to compose a two-dimensional network with each tin atom being fi~e-co-ordinate.~ The selenide and telluride Rb,GeX (X =Se Te) result from Rb,CO, Ge and the chalcogen on heating.The selenium derivative comprises chains of GeSe tetrahedra connected through Se-Se bonds with terminal (227-230 pm) and bridging (242-243.7pm) Ge-Se bonds. In addition Rb,Ge,Se,,.MeOH is formed and has an adamantane-like structure with terminal Ge-Se bonds of 225pm and cage ones of 234-239~m.~~ Reducing the alloy Bi,Sn,Se with potassium in the presence of [PPh,]Br gives [PPh,],[Sn,Se,Ph,]. The anion has a square-planar Sn,Se ring with trans phenyl groups and trans exo selenium atoms.86 Oxidative addition of SiH,Ph to [Rh(SR)(PMe,),] (R =aryl) gives the complex mer-[RhH(SiHPh,)(SR)(PMe,),] which isomerizes through SR transfer to Si to give the complex ~~c-[R~H,(S~P~,SR)(PM~,),].~~ The first 2,4,5~trithia-1,3-disilabicyclo[ 1.1.llpentaneresults from the desulfurization of the tetrathia[2.l.l]hexane itself resulting as the major product of the pyrolysis of (Me,Si),CSiH with an excess of sulfur in decahydronaphthalene.The Si * -Si distance of 240.5pm is within the range of Si-Si single bonds. The germanium-selenium analogue can be prepared similarly and shows the bridgehead Ge **-Ge bond slightly longer than the single bond value.88 Sulfur reacts with [GeH,(mes)(R)] {R =C,H,[CH(SiMe,),],-2,4,6} at 160 "C to give the tetrathiagermolene. With Ph,CN, the heterocycles (30k(32) result [equation (16)].89 The stannylene :SnR(R') (R =C,H,Pr',-2,4,6) and selenium form monomeric Se=SnR(R') which gives heterocycles with PhNCS R"CN-+O (R" =aryl) and styrene Carbon Silicon Germanium Tin and Lead oxide the former giving the dithia- and diselena-stannetanes (33) and (34) and not the mixed derivative.With CS, the 1 1 adduct results and with an excess of CS, gives the unsymmetric olefin (35) which thermolyses to the symmetric olefin (36) through CS loss while olefins add to the 1 1 adduct to give cyclic products (37) (Scheme 4).” The plumbylene :PbR(R’) and sulfur give the tetrathiapl~mbolane.’~ The novel gaseous cation F,SiXe+ results from the displacement of HF from protonated SiF in the gas phase with Xe and has C, symmetry and a Si-Xe bond length of 254.1 Reacting SiPh,OH with HF and NBu”,F gives the salt [NBu”,][SiF,Ph,].This readily fluorinates alkyl halides and p-toluenesulfonates. Similarly 4,4’-[(EtO),Et- Si],biphenyl gives the trifluorosiliconate with HF-NBu”,F or HF-KF-18-cr0wn-6.~~ The salts M+[SiF,(C,F,)]- result from MF (M = K Cs NMe,) and SiF,(C,F,) in PhNCS R R ,Se -Sn/’>NPh + Sn PNPh RI’ \Se R” \s Scheme 4 D. A. Armitage MeCN or bis(2-methoxyethyl) ether and react readily with electrophiles with cleavage of the aryl-Si bond.' The intramolecular fluoride donor-acceptor system involving m-and [p-(difluorophenylsilyl)phenyl]trifluorophenyl silicate undergoes bimolecular exchange through a cyclophane-like transition state on the basis of the 13C NMR spec tr um.The tetrahedral [(Al(cp*)},] reacts with two moles of SiF,Ph to give fluoride addition across four of the Al-A1 bonds and SiPh insertion into the other two. The resulting eight-membered A14F4 ring is therefore bridged by two SiPh groups with A1-Si bonds 245.1 pm [equation (17)].96 The chelating halide-ion acceptors Ph,XSn(CH,),SnXPh (X = F C1 Br I; n = 1,2 3) all chelate a single halide ion fluoride preferentially while for n = 1 an excess of fluoride gives the dianions [Ph2F2SnCH,SnF,Ph2]2-.97The SnF,- anion crystal- lizes as a discrete trigonal pyramid in [SnF,],[Ni(H,O),] with Sn-F 204-206 ~m.'~ Lead@) iodide reacts with NaI and NBu",PF to give the complex iodide-bridged anion Pb,& with D, symmetry in which each lead atom is octahedrally co-ordinated to six iodine atoms.These octahedra are connected through layers comprising 1,4,8,4 and 1 lead atoms respectively in a Chinese-puzzle type of arrangement." The salt [PbI(18-crown-6)] '1,-(38) results from PbI and 18-crown-6 with iodine in CH,C1 and occurs as weak ion pairs with the cationic Pb-I interaction of 290.1 pm and that between Pb and the 1,-ion 381.4-387.9pm.100 TI+ .'pb/ I.0-* (18-crown4 omitted \ ,,' forclarity) 1 'I (38) The complex [NBu",],[PtX(C,F,),] (X = C1 I) with lead(1r) perchlorate gives luminescent dinuclear complexes with a mixed chloride-lead bridge between the two platinum atoms [(F5C,),Pt(~-C1X~~-Pb)Pt(c6F5)3]2-(39). The structure indicates Pt-Pb bond lengths of about 272-273pm7 a PtPbPt angle of 85.25" and six weak interactions between the ortho-fluorine atoms and lead of 282-303 pm.Hydrolysis of the chloride gives the hydroxide."' Carbon Silicon Germanium Tin and Lead 67 References 1 D.A. Plattner and K.N. Houk J. Am. Chem. Soc. 1995,117,4405. 2 U. H. F. Bunz V. Enkelmann and F. Beer Organometallics 1995,14,2490. 3 M.-M. Rohmer M. Benard,C. Bo and J.-M. Poblet J. Am. Chem.Soc. 1995,117,508;Y. G. Byun C. S. 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