The mechanism of the collision-induced loss of methane from the trimethylsilyl negative ion

Abstract

Collisional activation of Me₃Si^– induces major losses of H˙, H₂, and CH₄. Loss of H₂ forms deprotonated dimethylsilene, ab initio calculations (6-31 + G) indicate the structure of the product to be Me–Si[graphic omitted]. Loss of methane could, in principle, occur by two ionic pathways, viz.(i) by initial formation of an incipient hydride ion which then removes a methyl cation by an S_N2 process, or (ii) by formation of a bound methyl anion which effects deprotonation of a methyl group. Ab initio calculations suggest that the latter process is more energetically favoured and that the lowest energy pathways is the concerted route Me₃Si^–→[Me^–(Me₂Si)]‡→ MeiCH₂+ CH₄.