Trapping Experiments on a Trichlorosilanide Anion: a Key Intermediate of Halogenosilane Chemistry.

Treatment of SiCl with [EtN][BCl] in CHCl furnished the known products of a chloride-induced disproportionation reaction of the disilane, such as SiCl, [Si(SiCl)], and [SiCl·2Cl]. No Si-B-bonded products were detectable. In contrast, the addition of SiCl to [EtN][BICl] afforded the Si-B adduct [EtN][ISiBI]. Thus, a quantitative Cl/I exchange at the silicon atom accompanies the trihalogenosilanide formation. [EtN][ISiBI] was also accessible from a mixture of SiI, [EtN]I, and BI. According to X-ray crystallography, the anion [ISiBI] adopts a staggered conformation with an Si-B bond length of 1.977(6) Å. Quantum-chemical calculations revealed a polar covalent Si-B bond with significant contributions from intramolecular I···I dispersion interactions.