Catalysis in aqueous solution: Hydrogenation of benzene derivatives catalysed by (eta(6)-C6H6)(2)Ru2Cl4

The catalytic hydrogenation of various benzene derivatives was studied, using (eta(6)-C6H6)(2)Ru2Cl4 in aqueous solution as the catalyst precursor. Under biphasic conditions, the corresponding cyclohexane derivatives are obtained with catalytic turnover rates which vary, depending on the substrate, from 20 to 2000 cycles per h. After a catalytic run, the aqueous solution contains the two tetranuclear cations [(eta(6)-C6H6)(4)RU4H4](2+) and [(eta(6)-C6H6)(4)Ru4H6](2+) which are known to catalyse the hydrogenation of aromatic compounds, but the activity of which is considerably lower than that of the (eta(6)-C6H6)(2)Ru2Cl4 precursor. An intermediate, presumably the more active species, was detected by H-1-NMR spectroscopy under catalytic conditions and identified as the trinuclear cluster cation [Ru-3(eta(6)-C6H6)(3)(mu(2)-Cl)(mu(3)-O)(mu(2)-H)(2)](+). (C) 1998 Elsevier Science B.V. All rights reserved.