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 (MeOCH2CH2OCH2-CH2-NHC) functionality on N-1 and bulky benzyl groups (CH2-C6H2(CH3)(3)-2,4,6 and CH2-C-6(CH3)(5)) on N-3 of (5,6-dimethyl)benzimidazole were synthesized by deprotonation of the corresponding benzimidazolium salt with [Rh(mu-OMe)(1,5-cod)](2) in dichloromethane at ambient temperature. All compounds have been fully characterized by elemental analysis, H-1 and C-13 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. (C) 2010 Elsevier B. V. All rights reserved.