Catalysis in aqueous solution: Hydrogenation of benzene derivatives catalysed by ( η6-C 6H 6) 2Ru 2Cl 4

Abstract

The catalytic hydrogenation of various benzene derivatives was studied, using ( η 6-C 6H 6) 2Ru 2Cl 4 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 [( η 6-C 6H 6) 4Ru 4H 4] 2+ and [( η 6-C 6H 6) 4Ru 4H 6] 2+ which are known to catalyse the hydrogenation of aromatic compounds, but the activity of which is considerably lower than that of the ( η 6-C 6H 6) 2Ru 2Cl 4 precursor. An intermediate, presumably the more active species, was detected by 1 H -NMR spectroscopy under catalytic conditions and identified as the trinuclear cluster cation [Ru 3( η 6-C 6H 6) 3( μ 2-Cl)( μ 3-O)( μ 2-H) 2] +.