The reactions of [tris(trimethylsilyl)methyl]silicon halides and hydrides with electrophilic reagents

Abstract

A study has been made of the reactions of compounds of the type (Me 3Si) 3CSiR 2X (e.g. X = I, R 2 = Me 2, Ph 2, PhMe, Et 2, or EtMe; X = H, R 2 = Me 2, Et 2) with electrophilic reagents such as Ag NO 3, AgOAc, AgO 2CCF 3, Hg(NO 3) 2, Hg(OAc) 2, HgCl 2 and HgBr 2, in alcohols, AcOH, CF 3CO 2H, or mixtures of these. Reactions of (Me 3Si) 3 CSiPh 2I take place exclusively with rearrangement, to give products of the type (Me 3Si) 2C(SiMe 2Y)(SiPh 2Me) (e.g. with AgNO 3i-PrOHMeOH, a mixture of products, with Y = NO 3, OMe or OPri is formed), while the compounds TsiSiR 2I with R 2 = Et 2, PhMe, or EtMe give both rearranged products, (Me 3Si) 2CH(SiMe 2Y)(SiR 2Me), and unrearranged products, (Me 3Si) 3CSiR 2Y. With AgNO 3 or Hg(NO 3) 2 in MeOH, added NaNO 3 does not increase the SiONO 2/SiOMe product ratio. The reactions of (Me 3Si) 3CSiMe 2H and (Me 3Si) 3CSiMe 2I with Hg(NO 3) 2AcOHMeOH give virtually the same product distribution, as do those of (Me 3Si) 3CSiMe 2I and (Me 3Si) 3SiMe 2Br with AgNO 3MeOH. (The bromide reacts much more slowly than the iodide in the latter case, and no reaction was observed in the case of (Me 3Si) 3CSiMe 2Cl). The iodide (Me 3Si) 3SCiMe 2 I undergoes solvolysis slowly in CF 3CO 2H alone, and added NaO 2CCF 3 has no effect. The results are interpreted in terms of the formation of a cationic intermediate by abstration of X − from (Me 3Si) 3CSir 2X by the electrophile. A structure involving a Me group bridging the 1- and 3-silicon atoms is favoured for this cation, with the nucleophile subsequently attacking at either of these atoms.