Comparison of Ru(II)‒arene complexes containing naphthyl-/quinolinyl-substituted ligand vis-a-vis structure, spectra and catalytic activity

A series of ligands with naphthyl/quinolinyl substituent in their principal molecular framework were synthesised. Their corresponding half-sandwich ruthenium (Ru) complexes (Ru1a-b, Ru2a-b and Ru3) were then successfully generated. The structure of all synthesised compounds was comprehensively elucidated via 1H and 13C nuclear magnetic resonance (NMR), elemental analysis and Fourier-transform infrared spectroscopies. Notably, the structural configuration of Ru3 was delineated via X-ray diffraction. The catalytic efficacy of the Ru complexes was systematically probed in two distinct reactions: 1) transfer hydrogenation (TH) of ketones using 2-propanol as the hydrogen source and 2) reduction of nitroarenes to anilines using sodium tetrahydridoborate as the reducing agent in ethanol, conducted at ambient temperature. Comparative analysis of catalytic yields of the Ru complexes (Ru1a-b, Ru2a-b and Ru3) in both reaction types revealed that Ru3 delivered superior catalytic performance in both types of reactions. Furthermore, scrutiny of the 1H-NMR spectrum during the TH reaction revealed formation of Ru-hydride species.