Germylenes formation

Three-membered heterocycles of type 161 or 163 can also be used for germylene formation and for the synthesis of germole derivatives <1999JA8811, 1994JOM(482)131>. 

Decomposition with the elimination of arsenic or phosphorus ylide and formation of silylene (germylene, stannylene) Me2E14, which represents the process inverse to the synthesis of these betaines. 

The formation of betaines in the reaction of silylenes (germylenes, stannylenes) Me2E14 (E14 = Si, Ge, Sn) with ylides H2C=E15Me3 (E15 = P, As) under gas-phase conditions occurs without a barrier as a strongly exothermic process. The thermal effects of the reactions are presented in Table XVII. 

Oxadative addition reactions of germylenes are a versatile method for the formation of germanium-pnictogen bonds.147-156 Reaction of germylenes with diazabutadienes yields [4+ 1]-cycloaddition products (Equation (115)),148... 

A germanium-nitrogen complex containing two Ge atoms disposed in an acyclic array was obtained via the formation of the intermediate germylene [(Me3Si)2N]GeCl, which was converted into a germanium(iv) adduct via an insertion reaction (Scheme 19).157... 

Germylenes can be released thermally in the presence of a transition metal complex leading to the formation of a germanium-metal bond (Equation (193)).239 The reaction occurs at room temperature when a germylsilane is used as the synthon (Equation (194)).240... 

The formation of transient 1,2-digermacyclobutadiene 9179 was postulated in the reaction of TsiGeCl LiCT 3THF78 with Mg in the presence of diphenylacetylene. This reaction could involve the formation of the digermyne intermediate 92 generated from 93 formed by dimerization of the germylene anion radical 94 [Eq. (18)]. 

Attempts to trap the digermene 74 in solution with benzil afforded only the cycloadduct 109 because of the [1 + 4] cycloaddition with germylene 10863 [Eq. (26)]. Another proof of the formation of germylene 108 in solution from 74 was given by cryoscopic studies.63... 

Physical properties of 177131 parallel those previously mentioned for the germanimine 142 (stemming from the same germylene 140), particularly the formation of pairs of enantiomers in the solid state, an analogous marked shortening of the Ge=S distance [d Ge=S 2.090(2) A] in comparison to the common Ge-S single bond length (2.26 A), and the temperature dependence of the 1H NMR spectrum. 

An immediate reaction takes place between 178 or 179 and 3,5-di-tert-butyl-l,2-benzoquinone to lead to the dioxagermole 189, the formal adduct of the germylene (ArO)2Ge with the quinone. A single electron mechanism, supported by an ESR study and depicted in Scheme 37, was postulated to account for the formation of 189.132... 

The other important type of reaction leading to the formation of two bonds between a metal and four-atom fragment is addition of carbenoids, i.e. germylenes and stannylenes, to a-dicarbonyl and related compounds. The process can be classified as redox (4 + 1) cycloaddition since the dicarbonyl fragment is reduced while the carbenoid is oxidized. Formally the simplest example of such reactions is the interaction of methylglyoxal with activated tin metal to give a cyclic stannylene, Sn(II) enediolate (see Scheme 34) <83CL1825>. 

The cycloaddition reaction of singlet GeX2 (X = F, Cl) with formaldehyde was studied employing the HF/6-311+G theory.106 The reaction proceeds in two steps barrierless formation of an intermediate complex followed by rate-determining isomerization to form the product. The results were compared with those from other cycloadditions of germylenes and silylenes. 

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