Reaction of alkyl and silalkyl halides with organometallics

Abstract

We have observed contrary to previous observations that (3- bromopropyl)triphenylsilane reacts with magnesium to give reasonable yields of the corresponding Grignard reagent. The same Grignard reagent is produced by metal exchange from the reaction of (3- bromopropyl)triphenylsilane with alkyl Grignards. In contrast methyltriphenylsilane is the major product from the reaction of bromomethyltriphenylsilane with alkyl Grignard reagents in ethereal solvents, however in benzene some metal transfer takes place and the SiCH MgBr is obtained in about forty per cent Grignard reagent Ph3 2 yield, Such metal transfer reactions are not observed with similar alkyl halides and must arise due to the enhanced carbanion stability in the silicon systems. Chloromethyltriphenylsilane with sodium in alcohol undergoes a rearrangement which involves migration of a phenyl group from the silicon atom to the adjacent carbon atom. It has been suggested that such rearrangements are promoted by nucleophilic participation at silicon, our results indicate an electron transfer type mechanism and the intermediacy of a carbanionic species. Similar re- arrangements are observed in the reaction of chloromethyltriphenyl- silane with n-butyllithium and silver chloride and when iodomethyl- triphenylsilane is treated with potassium hydroxide in aqueous ethanol.