Characterization of hydrogen-substituted silylium ions in the condensed phase.
basic_science · Level V
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- Record sourced from PubMed, PMID 31296768.
- Also identified by DOI 10.1126/science.aax9184.
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Abstract
Hydrogen-substituted silylium ions are long-sought reactive species. We report a protolysis strategy that chemoselectively cleaves either an Si-C(sp<sup>2</sup>) or an Si-H bond using a carborane acid to access the full series of [CHB<sub>11</sub>H<sub>5</sub>Br<sub>6</sub>]<sup>-</sup>-stabilized R<sub>2</sub>SiH<sup>+</sup>, RSiH<sub>2</sub> <sup>+</sup>, and SiH<sub>3</sub> <sup>+</sup> cations, where bulky <i>tert</i>-butyl groups at the silicon atom (R = <i>t</i>Bu) were crucial to avoid substituent redistribution. The crystallographically characterized molecular structures of [CHB<sub>11</sub>H<sub>5</sub>Br<sub>6</sub>]<sup>-</sup>-stabilized <i>t</i>Bu<sub>2</sub>HSi<sup>+</sup> and <i>t</i>BuH<sub>2</sub>Si<sup>+</sup> feature pyramidalization at the silicon atom, in accordance with that of <i>t</i>Bu<sub>3</sub>Si<sup>+</sup>[CHB<sub>11</sub>H<sub>5</sub>Br<sub>6</sub>]<sup>-</sup> Conversely, the silicon atom in the H<sub>3</sub>Si<sup>+</sup> cation adopts a trigonal-planar structure and is stabilized by two counteranions. This solid-state structure resembles that of the corresponding Brønsted acid.