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 5. 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.