Hydrogenation of imines catalyzed by ruthenium(II) complexes containing phosphorus-nitrogen ligands via hydrogen transfer reaction

This work describes the synthesis and characterization of Ru(II) compounds with general formula cis-Cl- cis-P cis-N- RuCl₂(PN)₂ (where PN represents a heterobidentate PN-donor chelated ligand) and their application as catalysts in the reduction of acetophenone and imines hydrogenation via hydrogen transfer reaction using 2-propanol as the hydrogen source. Single crystal diffraction analysis for all synthesized ruthenium complexes shows non-regular octahedral coordination around the metal. All the synthesized Ru(II) complexes achieved high conversions and turnover frequencies in hydrogen transfer reaction to acetophenone (830 h⁻¹) and imine hydrogenation (760 h⁻¹ for N-benzylideneaniline). The complex (dichloro bis-(8-(diphenylphosphino)quinoline)ruthenium(II)) (RuL2) achieved high conversion in imine hydrogenation, while the complex(dichloro bis-(N-(diphenylphosphino)pyridin-2-amine)ruthenium(II)) (RuL3) showed high conversion in acetophenone reduction. It was found that the electronic, structural, and steric properties of the ligands could influence catalytic performance.