Catalytic hydrogenation of benzene derivatives under biphasic conditions

Abstract

The catalytic hydrogenation of various benzene derivatives was studied, using the salt [(η6-C6H6)4Ru4H4]Cl2 in aqueous solution as the catalyst precursor. Under these biphasic conditions, the corresponding cyclohexane derivatives are obtained with catalytic turnover rates of more than 100 cycles per hour. In the case of the hydrogenation of the parent benzene, the NMR analysis of the aqueous phase revealed the presence of the hexahydrido species [(η6-C6H6)4Ru4H6]2+ together with the tetrahydrido species [(η6-C6H6)4Ru4H4]2+ under hydrogen pressure. An exchange study of the reaction of the para-cymene analogue [(η6-C6H4MePri-p)4Ru4H4]2+ with benzene showed the four arene ligands in the tetrahydrido cluster to be successively replaced by other aromatic ligands under catalytic conditions.