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.