Arene hydrogenation with a stabilised aqueous rhodium(0) suspension: A major effect of the surfactant counter-anion

A reduced aqueous colloidal suspension of rhodium shows an efficient activity in the catalytic hydrogenation of various benzene derivatives under biphasic conditions at room temperature and under atmospheric hydrogen pressure. The rhodium nanoparticles in the size range of 2 - 2.5 nm have been synthesised by reducing RhCl3 . 3 H2O with sodium borohydride and were stabilised by highly water-soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium salts (HEA16X, X = Br, Cl, I, CH3SO3, BF4). The major influence of the counter-ion of these surfactants on catalytic activity and recycling is described. The best results have been obtained with chloride ammonium salts HEA16Cl.