Solution and solid-state structure of 2- And 4-bis(trimethylsilyl) methylpyridinium cations

Abstract

N-Methylation of the 2- and 4-bis(trimethylsilyl)methyl pyridines 7 and 9 gives the ions 5 and 6 and results in a significant decrease in the 13CH-29SiMe3 coupling constant, consistent with increased C-Si-π hyperconjugation between the trimethylsilyl substituents and the electron-deficient aromatic system of the pyridinium cations. The rotation barrier about the Cipso-CH bond, which was measured for both 5 and 7 using variable-temperature 13C NMR and calculated at the B3LYP/6-311G** level, reveals that steric effects make a larger contribution than hyperconjugative effects to this barrier. The crystal structure of the protonated salt 11 shows that the conformation of the CH(SiMe3)2 substitue..