EVIDENCE FOR THE EXISTENCE OF SILYLIUM CATIONS IN CONDENSED PHASES

Ab initio geometry optimizations, Si-29 NMR chemical shift calculations, and bond density investigations refute recent claims about the existence of silylium cations R3Si+ (R=Me, Et) in aromatic solvents. The alleged silylium cations react in these solutions by an electrophilic attack at the aromatic solvent molecule yielding a Wheland sigma complex. However, ab initio calculations also indicate that it should be possible to generate fairly free silylium cations in aromatic solvents provided an electrophilic attack is sterically and/or electronically hindered.