J. Satgé

Un Nouveau diphosphene stable: Le bis[tris(trimethylsilyl)methyl] diphosphene

Abstract A new stable diphosphene (Me 3 Si) 3 CPPC(SiMe 3 ) 3 has been isolated and characterized particularly by its NMR data; the 31 P NMR chemical shift appears to be the largest ever observed.

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.

Multiply Bonded Germanium Species

Publisher Summary The fact that intermediates with silicon doubly bonded to carbon, oxygen, sulfur, nitrogen, or silicon have been described and fully characterized for several years, and no such germanium intermediate was described until 1973. Intermediates with germanium doubly bonded to carbon, oxygen, sulfur, nitrogen, phosphorus, and germanium are, like their silaanalogs, very unstable. The germanones thus generated were identified by various trapping reactions with methoxygermanes, oxagermacyclopentane, and ethylene oxide. The reactivity of azide increases with the electrophilic character of germylenes. This fact is consistent with a nucleophilic attack of azide on germylene leading to bipolar intermediate, which decomposes generating nitrogen and forming the germaimine. Germaphosphimine and silaphosphimine species with germanium or silicon doubly bonded to dicoordinated phosphorus can be obtained from 2-germa or 2- silaphosphetanes by a thermal β-decomposition reaction. In the study of GeH 2 , Kraus claimed it likely that dihydride is a dimer with doubly bonded germanium atoms and that upon the addition of sodium one bond is broken to form the salt NaH 2 GeGeH 2 Na. The first theoretical studies on germanium doubly bonded intermediates were carried out by Gowenlock and Hunter. The instability of germanium doubly bonded intermediates makes the spectroscopic observation and measurement very difficult. Doubly bonded germanium species, as well as germylenes, are of great fundamental and practical interest. These intermediates are powerful synthetic reagents in organometallic chemistry.

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.

Les sila-2 phosphetannes precurseurs de sila-phosphimines

Abstract The first 2-silaphosphetane was synthetized by reaction of butyllithium with a β-chlorosilylphosphine, followed by intramolecular cyclisation. Physicochemical data show the existence of an equilibrium between the monomeric form (2-silaphosphetane) and the dimeric form (2,6-disila-1,5-diphosphocane). Thermic decomposition under reduced pressure of the 2-dimethylsila-1-phenylphosphetane, through a β-elimination process, leads to the dimethylsilaphenylphosphimine; this new species with a SiP double bond has been characterized by formation of the dimer (Me 2 SiPPh) 2 and by insertion reaction of the 2-silaphosphetane into the SiP bond.

Digerma-2,4 thiétannes et tétragermadithiocannes, précurseurs de germathiones et germaéthylènes

2,2,4,4-Tetramethyl 2,4-digermathietane (I) is synthesized by treating bis(chlorodimethylgermyl)methane with Na2S (THF). I is relatively stable in solution at room temperature but simultaneously dimerizes and easily dissociates upon heating. The decomposition reaction proceeds with formation of germathione and germaethylene and leads to 2,2,4,4,6,6-hexamethyl-2,4,6-trigerma-1,3-dithiane (II) and 2,2,4,4,6,6-hexamethyl-2,4,6-trigermathiane (III). Pyrolysis of 2,2,4,4,6,6,8,8-octamethyl-2,4,6,8-tetragerma-1,5-dithiocane (di-germathietane dimer) at 230°C leads to the same heterocycles, II and III. Molecular cyclo-elimination mechanisms explain the thermal decomposition, which proceeds via dimethylgermathione and 1,1-dimethyl-1-germaethylene intermediates.

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.

Addition des germyl- et silylphosphines aux aldehydes et cetones α-ethyleniques

Abstract Germyl- and silyl-phosphines R 3 MPR′ 2 (M = Ge, Si) generally add in 1-4 position to α-ethylenic aldehydes and ketones with formation of phosphorus alkenoxy-germanes or -silanes. The α-ethylenic aldehydes always lead to 1-4 Z and E adducts ( Z preponderant), α-ethylenic ketones exclusively to the Z isomer. This particular stereochemistry is explained by a mechanism involving initial nucleophilic attack of the metal phosphine on carbon 4, steric hindrance of the reaction intermediate and participation of a 6-center pseudo-cyclic complex. On the contrary 1-2 addition on the carbonyl group of the 9-fluorenone is exculsively observed. The orientation of the additions (1–2 or 1–4) is interpreted in terms of Pearson (HSAB) theory.