[R_3Si—arene]~+ cr Complexes in the Gas Phase

摘要

The report by Lambert et al. that an R_3Si~ + ion that is not coordinated to the anion and only weakly to the solvent exists in the solid [Et_3SiB(C_6F_5)_4 toluene] has stirred a controversy, mainly focused on the role of toluene. Schleyer et ai in agreement with Olah et al., argue that the compound is actually a salt of the arenium ion [Et_3Si toluene]~+, that is. a cr complex of type 1. According to Pauling, in the compound studied by Lambert et al. a cova-lent bond does exist between the Si atomand the para C atom of toluene moiecule, despite their large separation (2,18 A), and a significant fraction of the positive charge of Et_3Si~+ is transferred to the aromatic ring. Reed et al. recognize the existence of a covalent interaction between theEt_3Si group and the toluene molecule and assign the adduct the structure of a pi complex with an sp~2 carbon (2), rather than of the a complex I with an sp~3 carbon.