Half-Sandwich Ruthenium Complexes with Schiff-Base Ligands: Syntheses, Characterization, and Catalytic Activities for the Reduction of Nitroarenes

A series of ruthenium(II) p-cymene complexes containing Schiff-base ligands [Ru(p-cymene)LCl] [HL = pyridyl-salicylimine (2a-2d); HL = thiazol-salicylimine (2e-2h); HL = benzothiazol-salicylimine (2i-2I] have been synthesized and characterized. All Schiff-base ligands and half-sandwich ruthenium complexes were fully characterized by H-1 and C-13 NMR spectra, mass spectrometry, and infrared spectrometry. The molecular structures of ruthenium complexes 2b and 2k were further confirmed by single-crystal X-ray diffraction methods. Furthermore, these half-sandwich ruthenium complexes are active catalysts for the mild hydrogenation of nitroarenes to aromatic anilines in the presence of sodium tetrahydroborate reducing agent in water. The most efficient catalyst, 2b, was found be compatible with nitroarenes of various functional groups.