Ruthenium(II) complexes bearing N-heterocyclic carbene ligands with wingtip groups and their catalytic activity in the transfer hydrogenation of ketones

A series of new silver(I) complexes bearing N-heterocyclic carbene (NHC) ligands with wingtip groups were synthesized by the reaction of 1,3-dialkylimidazolinium salts with silver(I) oxide in dichloromethane. The silver complexes were used as carbene-transfer agents to synthesize ruthenium(II) complexes with the general formula [RuCl2(NHC)(eta(6)-p-cymene)]. All the synthesized complexes were characterized by elemental analysis, FT-IR, H-1 NMR and C-13 NMR spectroscopy, and the molecular and crystal structure of 3d was determined by single-crystal X-ray diffraction. These ruthenium complexes were tested as catalysts in the transfer hydrogenation of ketones using (PrOH)-Pr-i as a hydrogen source. All compounds tested showed good catalytic activity in these reactions.