Solvated Silylium Cations: Structure Determination by NMR Spectroscopy and the NMR/Ab Initio/IGLO Method

Abstract

Sixty R3SiX/solvent (S) and R2HSiX/S systems with R = methyl, ethyl, butyl and S = methylene chloride, DMPU, DMSO, sulfolane, HMPA, acetonitrile, pyridine, N-methylimidazole, and triethylamine were investigated with the help of NMR spectroscopy for different concentration ratios of R3SiX/S and R2HSiX/S as well as different temperatures. With the help of measured δ29Si and δ13C chemical shifts as well as 1JSi-C and 2JSi-P coupling constants, typical NMR parameters for R3SiX and R2HSiX, R3Si(S)+, R2HSi(S)+, and R2HSi(S)2+ were established and discussed to distinguish between possible silylium cation−solvent complexes and equilibria between them. In addition, the NMR/ab initio/IGLO method (based on the continuum solvent model PISA and IGLO-PISA chemical shift calculations) was used to determine geometry, stability, and other properties of Me3Si(S)n+ and Me2HSi(S)n+ complexes in different solutions. NMR measurements and ab initio calculations clearly show that R3Si(S)+ and R2HSi(S)+ complexes with tetracoordi...