Substituent Effect on the Catalytic Activity of Ruthenium(II) Complexes Bearing a Pyridyl-Supported Pyrazolyl-Imidazolyl Ligand for Transfer Hydrogenation of Ketones
2015-11-09T00:00:00Z (GMT) by
Air- and moisture-stable ruthenium(II) complexes bearing a multisubstituted pyrazolyl-imidazolyl-pyridine ligand were synthesized and structurally characterized by NMR and X-ray single-crystal crystallographic analyses. The substituents on the imidazolyl moiety of the NNN ligand exhibited a remarkable impact on the catalytic activity of the corresponding Ru(II) complexes for transfer hydrogenation of ketones in refluxing 2-propanol, following the order NHTs > Me > H > NO<sub>2</sub>, to tune the catalytic activity. The highest final TOF value of 345 600 h<sup>–1</sup> was reached by means of 0.05 mol % of the Ru(II)-NHTs-substituted NNN complex as the catalyst. The corresponding structurally confirmed RuH complexes are proposed as the catalytically active species.