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

Abstract

Deprotonation of the bis(imidazolium) salt (1,1′-dimethyl-3,3′-ethylenediimidazolium dibromide, L·2HBr) with silver oxide in a solution mixture of CH₂Cl₂ and CH₃OH affords a silver carbene complex [Ag₂L₂]Cl₂ (1, L = 1,1′-dimethyl-3,3′-ethylenediimidazol-2-ylidene). With CH₃OH as the only solvent for the synthesis and after recrystallization in a chlorinated solvent in ambient condition, a polymeric silver complex [(L·2H)(Ag₂Br₄)]_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)RuCl₂]₂ and (p-cymene)Ru[S₂C₂(B₁₀H₁₀)] to yield the binuclear complexes [(p-cymene)RuCl₂]₂L (3) and {(p-cymene)Ru[S₂C₂(B₁₀H₁₀)]}₂L (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.