Characterization of hydrogen-substituted silylium ions in the condensed phase

Hydrogen-substituted silylium ions are long-sought reactive species. We report a protolysis strategy that chemoselectively cleaves either an Si-C(sp ) or an Si-H bond using a carborane acid to access the full series of [CHB H Br ] -stabilized R SiH , RSiH , and SiH cations, where bulky -butyl groups at the silicon atom (R = Bu) were crucial to avoid substituent redistribution. The crystallographically characterized molecular structures of [CHB H Br ] -stabilized Bu HSi and BuH Si feature pyramidalization at the silicon atom, in accordance with that of Bu Si [CHB H Br ] Conversely, the silicon atom in the H Si cation adopts a trigonal-planar structure and is stabilized by two counteranions. This solid-state structure resembles that of the corresponding Brønsted acid.