Silanes, trisubstituted, radical reactions

The reaction of thermally and photochemically generated tert-butoxyl radicals with trisubstituted silanes [Eqs. (6) and (7)] has been used extensively for the generation of silyl radicals in ESR studies, in time-resolved optical techniques, and in organic synthesis. Absolute rate constants for reaction (7) were measured directly by LFP techniques,56,62,63 whereas the gas phase kinetic values for reactions of Me3SiH were obtained by competition with decomposition of the tert-butoxyl radical.64,65... 

The addition of trisubstituted silanes to carbonyl sulfide has been applied to the synthesis of the corresponding silanethiol derivatives (Reaction 5.40) [78]. In Scheme 5.12 the mechanism is depicted, starting from the silyl radical attack to the sulfur atom of 0=C=S and ejection of carbon monoxide. The resulting silanethiyl radical abstracts hydrogen from the starting silane, to give the silanethiol and to generate fresh silyl radical (see Section 3.4). 

Aluminum trichloride catalyzed hydrosilation provides an interesting alternative to the free radical process. The addition of the silane was found to occur regioselectively at trisubstituted alkenes in a frans -fashion. Mechanistically it was concluded that the reaction proceeds via the addition of a silylenium cation to the multiple bond, generating the more stable (more substituted) carbocation, which abstracts a hydride from another molecule of hydrosilane (Scheme 2). ... 

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