Diether functionalized rhodium(I)–N-heterocyclic carbene complexes and their catalytic application for transfer hydrogenation reactions

N-heterocyclic carbene (NHC) complexes of rhodium(I) (3 and 4) bearing one diether (MeOCH2CH2OCH2CH2–NHC) functionality on N1 and bulky benzyl groups (CH2–C6H2(CH3)3-2,4,6 and CH2–C6(CH3)5) on N3 of (5,6-dimethyl)benzimidazole were synthesized by deprotonation of the corresponding benzimidazolium salt with [Rh(μ-OMe)(1,5-cod)]2 in dichloromethane at ambient temperature. All compounds have been fully characterized by elemental analysis, 1H and 13C NMR spectroscopy. X-ray diffraction studies on single crystals of 3a and 3b confirm the cis square planar geometry. All of the new benzimidazol-2-ylidene rhodium(I) complexes were found to be effective catalysts for the transfer hydrogenation reaction.