Half-Sandwich Ruthenium Phenolate–Oxazoline Complexes: Experimental and Theoretical Studies in Catalytic Transfer Hydrogenation of Nitroarene

In this work, five ruthenium complexes [Ru­(p-cymene)­LCl] containing phenolate-oxazoline ligands [L = 2-(4,5-dihydrooxazol-2-yl)­phenol (1); L = 2-(4-methyl-4,5-dihydrooxazol-2-yl)­phenol (2); L = 2-(4-ethyl-4,5-dihydrooxazol-2-yl)­phenol (3); L = 2-(4-phenyl-4,5-dihydrooxazol-2-yl)­phenol (4); and 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)­phenol (5)] were synthesized and characterized. The solid-state structures of all ruthenium complexes were determined by single-crystal X-ray diffraction. The catalytic activities of these complexes in the transfer hydrogenation reaction of nitroarene to aniline were investigated. Aniline and their derivatives were obtained in good to excellent yields with isopropanol as the hydride source. The present protocol provides an environmentally benign synthetic method for the reduction of nitroarenes to anilines without employing harsh reaction conditions. Theoretical studies employing density functional theory were carried with the aim to propose a feasible reaction mechanism and to draw insights into the reactivity of the half-sandwich ruthenium catalyst.