Reactions of stable silenes with Grignard reagents

Abstract

Grignard reagents have been found to add to members of the family of stable silenes (Me3Si)RSi=C-(OSiMe3)R′ (R = Me3Si, Ph; R′ = Ad or t-Bu). Two types of product were formed, namely a family of compounds where one molecule of Grignard reagent R″MgX was involved, leading to products with the structures 6, Me3SiOSiRR″CHR′(SiMe3), and a family where two molecules of Grignard reagent were involved, leading to products with structures 7, RR″2SiCHR′(SiMe3). The crystal structure of one compound, 6baa (R = Ph, R′ = Ad, R″ = Me), was obtained, confirming the structure assigned to this family of compounds. It is evident that, in the course of forming these products, a trimethylsilyl group originally attached to the sp2-hybridized silicon atom of the silene apparently underwent a 1,2-migration to the adjacent carbon atom (which had been sp2-hybridized in the parent silene). The original trimethylsiloxy group either underwent a reverse 1,2-rearrangement from carbon to silicon, forming 6, or else was eliminated during the reaction, yielding 7. The proportions of products 6 and 7 were found to be insensitive to the amount of Grignard reagent or the temperature at which the reaction occurred but were sensitive to the polarity of the solvent system, more product of structure 6 being formed in less polar solvents. In a related study it was shown that reaction of t-BuLi with a (polysilyl)acylsilane gave rise to a product in which a molecule of t-BuLi had added to a silene formed in the course of the reaction. Mechanisms explaining the formations of these products are given. © 1991 American Chemical Society.