NHTs Effect on the Enantioselectivity of Ru(II) Complex Catalysts Bearing a Chiral Bis(NHTs)-Substituted Imidazolyl-Oxazolinyl-Pyridine Ligand for Asymmetric Transfer Hydrogenation of Ketones

Pincer-type ruthenium(II)-NNN complex catalysts bearing a chiral bis(NHTs)-substituted imidazolyl-oxazolinyl-pyridine ligand were synthesized and structurally characterized by NMR, IR, elemental analysis, and X-ray single-crystal crystallographic determinations. The two NHTs groups substituted on the imidazolyl moiety of the chiral NNN ligand exhibited a remarkable effect on the enantioselectivity of the Ru(II)-NNN complexes for the asymmetric transfer hydrogenation (ATH) of ketones. The Ru(II)-NNN complex bearing a chiral (NHTs)2-substituted imidazolyl-(isopropyl)oxazolinyl-pyridine ligand exhibited excellent catalytic activity, reaching an enantioselectivity up to 99.9% ee for the target alcohol products.