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

Treatment of Si₂Cl₆ with [Et₄N][BCl₄] in CH₂Cl₂ furnished the known products of a chloride-induced disproportionation reaction of the disilane, such as SiCl₄, [Si(SiCl₃)₃]^-, and [Si₆Cl₁₂·2Cl]^2-. No Si-B-bonded products were detectable. In contrast, the addition of Si₂Cl₆ to [Et₄N][BI₃Cl] afforded the Si-B adduct [Et₄N][I₃SiBI₃]. Thus, a quantitative Cl/I exchange at the silicon atom accompanies the trihalogenosilanide formation. [Et₄N][I₃SiBI₃] was also accessible from a mixture of Si₂I₆, [Et₄N]I, and BI₃. According to X-ray crystallography, the anion [I₃SiBI₃]^- 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.