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

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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)(η6-p-cymene)]. All the synthesized complexes were characterized by elemental analysis, FT-IR, 1H NMR and 13C 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 iPrOH as a hydrogen source. All compounds tested showed good catalytic activity in these reactions.