Homolytic Organosilicon Group Transfer

As we showed previously in this chapter, silicon easily expands its valence shell to become a penta-coordinated species. Therefore, it is expected that an intramolecular transfer of organosilicon group from X to Y may occur via a radical mechanism, provided that the R substituents on the silicon atom are not good leaving groups (Reaction 6.20). 

Examples of 1,2 migration of silyl group from silicon to other atoms are also well documented. Reaction (6.21) that involves a transfer from silicon to carbon has been observed in the gas phase at elevated temperatures [35], From the measured Arrhenius parameters, i.e. logA/s = 12.3 and = 90kJ/mol, it is clear that the reaction is unimportant around room temperature. However, this type of reaction is probably the essential step in the formation of silicon-carbon fibres by pyrolysis of methylpolysilanes. 

Evidence that the 1,2 transfer of the Me3Si group from silicon to oxygen is an effective process (Reaction 6.24) has been obtained from a mechanistic investigation of the reaction of (TMS)3SiH with nitroalkanes and nitroxides [38,39], A lower limit rate constant of 10 s at room temperature was obtained for Reaction (6.24). 

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Homolytic 1,5 transfer of an organosilicon group from enoxy oxygen to alkoxy oxygen has also been observed [44]. As shown in Scheme 6.21, radical reaction of compoimd 92 with BusSnH afforded compound 93 in a 92% yield. 

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