Half-sandwich ruthenium(II) complexes containing 4-substituted aniline derivatives: structural characterizations and catalytic properties in transfer hydrogenation of ketones

Abstract

Four half-sandwich Ru(II) complexes (1)–(4) with the general formulae [Ru(η⁶-p-cymene)(L)Cl₂] were synthesized by the reaction of one equivalent of the Ru(II) p-cymene dimer with two equivalents of a p-substituted aniline derivative L (where L is p-methyl, p-isopropyl, p-methoxy, or p-hydroxy aniline). The structures of complexes (2)–(4) were determined by single-crystal X-ray diffraction studies. The structural analysis revealed piano-stool geometry at the Ru(II) ions which are coordinated to the η⁶-p-cymene, two chloride anions and the amine group of the aniline ligand. In the structure of (2)–(4), the coordinated chloride ions make intermolecular hydrogen bonding with the –NH₂ group of an adjacent molecules (NH–Cl) resulting in hydrogen bond networks. The catalytic activities of the complexes in transfer hydrogenation of acetophenone were studied. Complex [Ru(η⁶-p-cymene)(p-methylaniline)Cl₂] (1) showed the best catalytic performance in the transfer hydrogenation of acetophenone. The presence and positions of methyl and bromide groups on the acetophenone have an impact on the catalytic activity in transfer hydrogenation properties of the complex (1). Moreover, catalytic activity of the complex (1) is significantly higher in the transfers hydrogenation of cyclohexanone than 2-hexanone.