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 [CHBHBr]-stabilized RSiH, 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 [CHBHBr]-stabilized BuHSi and BuHSi feature pyramidalization at the silicon atom, in accordance with that of BuSi[CHBHBr] Conversely, the silicon atom in the HSi cation adopts a trigonal-planar structure and is stabilized by two counteranions. This solid-state structure resembles that of the corresponding Brønsted acid.