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.