Experimental and theoretical investigations into the manifestation of the γ-effect in 2- and 4-[2-silylethyl)]pyridines and pyridinium ions

Abstract

The γ-effect of the group 14 metals is a stabilizing interaction involving the back-lobe of the σC-M (M = Si, Ge, Sn, Pb) interacting with the developing carbocation γ to the tetrel. This percaudal interaction has been observed in solvolysis experiments with significant rate enhancements over unsubstituted systems, and subsequent isolation of three-membered ring products. In this study, the γ-effect is experimentally investigated in the solid phase with X-ray crystallography, the solution phase with Si-C coupling constants, and the gas phase via collision-induced dissociation (CID). Moving from 2- and 4-silylethyl substituted pyridines to the more electron demanding substituted pyridinium io..