Polysilane formation reaction intermediates

In 1971, a short communication was published [54] by Kumada and co-workers reporting the formation of di- and polysilanes from dihydrosilanes by the action of a platinum complex. Also the Wilkinson catalyst (Ph3P)3RhCl promotes hydrosilation. If no alkenes are present, formation of chain silanes occurs. A thorough analysis of the product distribution shows a high preference for polymers (without a catalyst, disproportionation reactions of the silanes prevail). Cross experiments indicate the formation of a silylene complex as intermediate and in solution, free silylenes could also be trapped by Et3SiH [55, 56],... 

Doubtless, in these reactions unstable intermediate silylmercury compounds such as [H2(CH3)Si]2Hg and [H(CH3)2Si]2Hg are first produced which then undergo decomposition. The formation of the trisilane and higher polysilanes from the reaction of (CH3)2SiHBr with Na/Hg may be rationalized by the insertion into [H(CH3)2Si]2Hg of dimethylsilylene, (CH3)2Si , which is probably produced during the reaction through decomposition of an unstable intermediate species (CH3)2SiHg, followed by decomposition of the adducts. The generation of dimethylsilylene and its insertion into the... 

Summary The formation of reactive intermediates via dehalogenation of chlorosilanes was investigated by using lithium powder and sonication. Whereas in the absence of a diene substrate mainly polysilanes are obtained, reactions with, e.g., dimethylbutadiene, yield the corresponding cycloaddition products, indicating silylenes and silaethenes as intermediates. 

The formation of silylmetallics by cleavage of Si—Si bonds with alkali metals is described in 5.5.42.1. Because Si—Si bonds can be formed by condensation of halosilanes with alkali metals, a direct route to silyl metallics should be possible by forming and reacting the disilane (or polysilane) with a metal without isolating the intermediate Si—Si-bonded species. However, this approach contains the same inherent restrictions as those described in 5.5.4.2.1 i.e., there must be one aryl group bonded to Si in the starting halosilane (see Table 1). Reaction of PhjSiCl does not occur with Na, but... 

Complexes bearing Pt-Si and Pt-Ge bonds have been invoked as potential intermediates in the formation of polysilanes ans polygermanes. The metallacycle [(Et3P)2Pt(/r-j] -H2CO)Ge(N(SiMe3)2)2] takes part of a photochemical cycloreversion reaction with Pt hydride formation, releasing CO. ... 

Other workers have reported that prolonged sonolysis of organolithiums derived from organic halides [94], chlorosilanes and chlorostannanes [95] results in Wurtz-type coupling. Yields are moderate and the reactions are of little synthetic interest. However, coupling of dichlorosilanes and stannanes produces a novel route to the cyclic polysilanes (9) and (10) (Scheme 37). The product obtained is determined by the steric bulk of the alkyl groups and only low levels of contamination by other silanes is observed [95]. Silylene intermediates did not appear to be involved. However, Boudjouk et al. [101] later reported formation of the tetramesityl silylene (11) which had previously been made by photolysis of (Mes)2Si(TMS)2 [102] (Scheme 38). 

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