Halogen exchange and expulsion: ligand stabilized dihalogen silicon dications

Abstract

The first ligand stabilized SiCl₂²⁺ dications were synthesized using N-methylimidazole as co-ordinating ligand. The compounds SiCl₄, SiBr₂Cl₂, and SiH₂Cl₂ form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si–N bonds of about 1.90 Å. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought and proceeds with considerable speed even without a catalyst.