Synthesis and characterization of the N-heterocyclic carbene ligand (NHC) precursors bearing long-alkyl chain substituent and the corresponding Ru(II)-carbene complexes for transfer hydrogenation catalysts

Abstract

A new series of Ru(II)-NHC complexes [RuCl2(NHC)(p-cymene)] (4a-e) were obtained through a transmetallation reaction of the corresponding Ag(I)-NHC complexes with [RuCl2(p-cymene)]2 in dichloromethane (DCM) under Argon atmosphere. All new compounds were characterized by NMR spectroscopy, elemental analysis, FT-IR, MS, and the molecular structure of 4a was determined by X-ray crystallography. The complex of 4a adopts three-legged piano stool geometry with the facial planar p-cymene representing the “seat”, and the two chloro and one NHC ligands form the three “legs”. All complexes have been tested as catalysts for the transfer hydrogenation of aromatic ketones, showing moderate to high activity in this reaction.