Coordination Chemistry of Bidentate Bis(NHC) Ligands with Two Different NHC Donors

Reaction of N-aminobenzimidazole 1 or N-aminoimidazole 2 with N,N-bis(dimethyleneamin)azine 3 yielded the biazoles 4-(benzimidazol-1-yl)-4H-[1,2,4]triazole 4 and 4-(imidazol-1-yl)-4H-[1,2,4]triazole S. Double N,N-alkylation yielded the new bis(NHC) precursors 1-methyl-4-(3-methylbenzimidazol-1-yl)-4H-[1,2,4]triazolium tetraffluoroborate [6a] (BF4)(2), 1-ethyl-4-(3-ethylbenzimidazol-1-yl)-4H-[1,2,4]triazolium tetrafluoroborate [6b](BF4)(2), and 1-methyl-4-(3-methylimidazol-1-yl)-4H-[1,2,4]triazolium tetrafluoroborate [7](BF4)(2), each featuring a triazolium moiety in addition to a benzimidazolium or imidazolium group linked together by a N-N bond. The diazolium salts react with Pd(OAc)(2) to give the bis(NHC) complexes [8a](BF4)(2), [8b](BF4)(2), and [9](BF4)(2), each bearing an unsymmetrical triazolylidene/benzimidazolylidene or triazolylidene/imidazolylidene dicarbene ligand coordinated in a chelating fashion to the metal center.