Halogen exchange and expulsion: ligand stabilized dihalogen silicon dications

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 A. 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 …