Synthesis, structure and transmetalation of N-heterocyclic carbene complex of silver. Evidence of halogen exchange during the synthetic process.

Deprotonation of the bis(imidazolium) salt (1,1'-dimethyl-3,3'-ethylenediimidazolium dibromide, L x 2HBr) with silver oxide in a solution mixture of CH(2)Cl(2) and CH(3)OH affords a silver carbene complex [Ag(2)L(2)]Cl(2) (1, L = 1,1'-dimethyl-3,3'-ethylenediimidazol-2-ylidene). With CH(3)OH as the only solvent for the synthesis and after recrystallization in a chlorinated solvent in ambient condition, a polymeric silver complex [(L x 2H)(Ag(2)Br(4))](n) (2) was formed. The presence of chloride in complex 1 and bromide in complex 2 indicates that a halogen exchange reaction occurred unambiguously during the synthesis and not during recrystallization. The silver-carbene complex 1 undergoes a facile reaction with [(p-cymene)RuCl(2)](2) and (p-cymene)Ru[S(2)C(2)(B(10)H(10))] to yield the binuclear complexes [(p-cymene)RuCl(2)](2)L (3) and {(p-cymene)Ru[S(2)C(2)(B(10)H(10))]}(2)L (4). The latter compound contains a carbene ligand and a 1,2-dicarba-closo-dodecaborane ligand. Molecular structures of complexes 1-4 were confirmed by X-ray single-crystal analyses.