Synthesis, Solid-state Structures, Solution Behaviour and Catalysis Studies of Nickel Complexes of Bis(benzimidazolin-2-ylidene)pyridine Pincer Ligands

Abstract

N-Heterocyclic carbene–nickel complexes with five- and four-coordinate geometries [(CNC)NiBr2] and [(CNC)NiBr]X (X = PF6 or BPh4) have been prepared with the pincer ligands 2,6-bis(N-octylbenzimidazolin-2-ylidene)pyridine and 2,6-bis(N-butyl-5,6-dimethoxybenzimidazolin-2-ylidene)pyridine. The addition of the n-octyl substituent significantly extends the solubility of the complexes and has allowed UV-vis solution studies of the complexes in dichloromethane and methanol. The four- and five-coordinate species exist in equilibrium in solution and this equilibrium has been explored by UV-vis studies. The complexes have also been characterized by NMR studies, and single crystal X-ray diffraction studies have been performed on [(CNC)NiBr2] (where CNC = 2,6-bis(N-octylbenzimidazolin-2-ylidene)pyridine) and [(CNC)NiBr]BPh4 (where CNC = 2,6-bis(N-butyl-5,6-dimethoxybenzimidazolin-2-ylidene)pyridine).