P. Riviere

Subvalent Group 4B metal alkyls and amides. Part 5. The synthesis and physical properties of thermally stable amides of germanium(II), tin(II), and lead(II)

A series of subvalent Group 4B metal amides of general formula M(NR1R2)2[(i) R1= SiMe3, R2= But; M = Ge, Sn, or Pb; (ii) R1= R2= SiMe3; M = Ge, Sn, or Pb; and (iii) R1= R2= GeMe3, SiEt3, or GePh3; M = Ge or Sn] has been prepared from the appropriate lithium amide and metal(II) halide. Under ambient conditions, the amides are pale yellow to red, thermochromic, diamagnetic, low-melting solids or liquids, and are soluble in hydrocarbons (C6H6 or C6H12) in which they are diamagnetic monomers. The lower homologues give parent molecular ions as the highest m/e species. Infrared spectra show a band at 380–430 cm–1[νasym(MN2)], and 1H or 13C n.m.r. spectra are consistent with the bent-singlet formulation. In the visible region the compounds exhibit a band (364–495 nm) of moderate intensity (Iµ= 600–2 050 dm3 mol–1 cm–1 in n-C6H14) indicative of an allowed electronic transition. Photolysis of each diamide in n-hexane in the cavity of an e.s.r. spectrometer affords (a) the persistent (t½ 5 min—3 months at 25° C) metal-centred radical Ṁ(NR1R2)3[(i) R1= SiMe3, R2= But, M = Ge or Sn; (ii) R1= R2= SiMe3 or GeMe3, M = Ge or Sn; or (iii) R1= R2= GeEt3, M = Sn], (b) a lead mirror (for the lead amides), or (c) no sign of reaction (for the more bulky diamides). E.s.r. parameters have been derived from the isotropic spectra.

Triaryl-silyl, -germyl, and -stannyl radicals .MAr3 (M = Si, Ge, or Sn and Ar = 2,4,6-Me3C6H2) and .Ge(2,6-Me2C6H3)3: Synthesis and ESR studies

Abstract The triarylmetal-centred radicals . MAr 3 (M = Si, Ge, or Sn; Ar = 2,6-Me 2 C 6 H 3 or 2,4,6-Me 3 C 6 H 2 ) have been prepared from the appropriate triarylmetal chloride, MAr 3 Cl, and an electron-rich olefin [R NCH 2 CH 2 NRC ] 2 (R = Me or Et) under UV irradiation in toluene at low temperature. The triarylgermyl radicals are persistent ( t 1 2 > 24 h, 20°C) whilst the analogous tin and silicon radicals are only stable under constant irradiation at temperatures below −20°C; the ESR spectra of the germanium radicals and of . Si(2,4,6-Me 3 C 6 H 2 ) 3 (which is the first triarylsilyl radical to be spectroscopically identified) show coincidental equivalence of all the proton couplings due to twisting of thearomatic rings into a “propeller” arrangement about the metal. The synthesis and characterisation of precursors to these radicals are also reported.

Synthèses et décomposition d'organométhoxygermanes et organométhoxyhalogénogermanes: Nouvelle méthode d'obtention de derivés organiques du germanium bivalent

Abstract The organomethoxy- and organomethoxyhalogermanes R2(MeO)GeH, R(MeO)GeH2, R(MeO)2GeH and R(MeO)(X)GeH (R = alkyl or phenyl) are synthesized by direct reaction at low temperature of sodium or lithium methoxides with the organohalogermanes R2(X)GeH, R(X)GeH2 and R(X)2GeH and by “chlorinemethoxy” exchange reactions between the same halohydrides and various methoxyorganogermanes. The instability of the organomethoxygermanes with GeH and GeO bonds lead to their decomposition with formation of divalent species of germanium and methanol. The “germylenes” 1 were characterized by condensation on the insaturated systems of 1,3-dienes and also by insertion into some σ-bonds.

Cycloaddition of germylenes to 3,5-di-t-butyl orthoquinone

Abstract The germylenes X 2 Ge, RGeX and R 2 Ge (X = halogen, OR; R = alkyl or aryl) react at room temperature with 3,5-di-t-butyl orthoquinone by regioselective cycloaddition. The corresponding substituted 2-germa-1,3-dioxolans are formed similarly in good yields, but their stabilities depend on the substituents on the metal. Some of them have also been synthesized by nucleophilic substitution from the corresponding chlorogermanes and 3,5-di-t-butyl catechol. 2-Halo(6,8-di-t-butyl)-4,5-benzo-2-germa-1,3-dioxolans undergo redistribution reactions, while the corresponding dialkyl or diaryl derivatives are very stable.

Addition des phénylgermanes et phénylchlorogermanes sur quelques composés carbonyles insaturés

Abstract Phenylgermanes and phenylchlorogermanes as a rule add to the double carboncarbon bond of α- and γ-ethylenic ketones upon radical catalysis of simple heating. However, the steric hindrance around the double ethylenic bond directs the addition of triphenylgermane to the carbonyl group of 2-methyl-2-hepten-6-one and mesityl oxide (l,4-addition). A certain electrophilic acitivity of phenyldichlorogermane is, however, observed: it gives ionic additions to the conjugated polarized systems of vinyl methyl ketone, mesityl oxide and ethynyl methyl ketone. In the addition of Ph 2 GeH 2 and PhClGeH 2 to α- and γ-ethylenic ketones an intramolecular cyclisation reaction of the mono-addition derivate occurs with the formation of a heterocycle with a GeOC bond. The tendency of the addition reaction of the organogermanium hydrides to diphenylketene is also closely linked to the polarity of the GeH bond in these hydrides and to steric effects.

Polygermanes precurseurs d'especes du germanium a coordinance non usuelle

Several thermal or photochemical α-elimination reactions of functional polygermanes lead to germylenes, R2Ge. Photolysis of polygermanes, cyclopolygermanes and polygermylmercury compounds and also hydrogen abstraction from various organohydropolygermanes using t-BuO., lead to the formation of polymetallated chains containing one or two germanium-centered radicals. These polygermyl radicals give germylenes, R2Ge, germanium centered radicals , α-digermyl diradicals (or digermenes) [ or ] and β- or γ-polygermyl diradicals via a homolytic monoelectronic α-elimination process. In some cases the formation of α-digermyl diradicals or digermenes can also be seen as occurring through dimerization of germylenes but with lower yields. All these intermediates have been characterized by several trapping reactions with dimethyl disulfide, 2,3-dimethylbutadiene or biacetyl.

Synthese de composes a liaison MIVBmercure. Precurseurs d'especes monovalentes (germynes), et bivalentes (germylenes), de radicaux centrometalles et d'intermediaires

Abstract Polynuclear germylmercury compounds are obtained from the reaction of organohydrogermanes Ph n GeH 4− n or digermanes Ph 2 n Ge 2 H 4− n ( n = 1, 2) with dialkylmercury R 2 Hg. Di- or tri-mercurated geminal polygermates thus synthesized generally present a low stability and undergo thermal- or photo-decompositions leading to the corresponding monovalent (germynes), divalent (germylenes) or, trivalent (germanium centered radicals) species and also to intermediate biradicals which could be considered as limit forms of germanium doubly-bonded compounds . Such intermediates have been chemically and spectroscopically characterized. Extension of these reactions to the silicon analogs met with difficulties, and thus previously observed differences between silicon and germanium chemistry were confirmed.

Synthese et etude spectrale uv de chaines polymetallees (Ge, Si); analyse theorique des effets de substitution

Abstract An UV study of polymetallic chains of Group IVB elements (Ge, Si) was developed. The studied polygermanes and polygermasilanes were mainly synthetized either by reaction of organolithium with organochlorogermanes or by a Wurtz type reaction. An enhanced λ max value for UV absorption of the chromophore Ge-Ge in these polymetallic compounds is observed in alkyl substitution at the metal by phenyl groups or halogen and also when the polymetallic chain is lengthened. A theoretical approach of these phenomena is proposed based on excitonic coupling between phenyl and metallic chain transition moments.

Intermediaires organiques du germanium divalent : I. Polygermanes precurseurs de phenylgermylenes fonctionnels

Abstract Functional polygermanes PhY 2 GeGeY 2 Ph, (PhY 2 Ge) 2 GeYPh and (PhY 2 Ge) 3 GePh (Y = MeO, Me 2 N, Et 2 ) are obtained in exchange reactions between the corresponding phenylchloro-di and -poly-germanes and functionnal trialkylgermanes R 3 GeY, or in reactions of organometallic derivatives YM (M = Li, Na or MgX) with the same chloro-di- and -poly-germanes. The thermal decomposition of these polygermanes by an γ-elimination mechanism gives new functional organic germylenes PhGeY isolated or characterized by cycloaddition on dimethylbutadiene. Phenylhydrogermylene and diphenylgermylene are generated in the catalysated decomposition of phenylhydrodigermanes, PhH 2 GeGeH 2 Ph and Ph 2 HGeGeHPh 2 , by germyllithium derivatives. A decomposition mechanism with participation of a germylanion is formulated.

Reactions d'insertion de fluorogermylenes sur diverses liaisons σ. Nouvelles syntheses de derives polymetalles du groupe IVB

Abstract Difluorogermylene which exhibits a strong carbene activity gives many insertion reactions in σ bonds. In the same type of reactions, the lower reactivity of phenylfluorogermylene is generally similar to reactivity of the phenylchlorogermylene. The polymetallated derivatives of Group IVB metals formed by insertion reactions of these germylenes in σ bonds, like metalhalogen, metalhydrogen, metaloxygen, metalsulfur, metalnitrogen and metalmetal bonds, have low stability and thermally decompose via α-elimination processes to form germylenes and fluoro-organometallics. The polymetallated derivatives have been characterised by spectroscopy and chemical investigations: alkylation or arylation of their M(IVB)X bonds (X = halogen, oxygen etc.). The insertation reactions of difluoro-, phenylfluoro- and phenylchloro-germylenes into the intracyclic germaniumoxygen bond of diastereoisomeric oxaermacycloalkanes are generally stereospecific and can be interpreted by a concerted mecanism.