Synthesis, characterization and crystal structures of silver(I)– and gold(I)–N-heterocyclic carbene complexes having benzimidazol-2-ylidene ligands

A series of N,N′-disubstituted benzimidazolium salts (1–3) were prepared via the successive N-alkylation method. Cationic, linearly coordinated silver(I)–NHC complexes (4–6) were synthesized in good yield by the reaction of Ag2O with salts 1–3. The corresponding cationic gold(I)–NHC complexes (7–9) of silver(I)–NHC derivatives were prepared by the technique of transmetallation at mild reaction condition. The new azolium salts and their carbene complexes were characterized by 1H and 13C NMR and FTIR spectroscopy, and elemental analysis. Additionally, benzimidazolium salts 2 and 3, silver(I)–carbene complexes 4a and 6a, and gold(I)–carbene complex 8 were structurally characterized by single crystal X-ray diffraction technique.