Stabilized rhodium(0) nanoparticles: a reusable hydrogenation catalyst for arene derivatives in a biphasic water-liquid system.

A colloidal system based on an aqueous suspension of rhodium(o) nanoparticles proved to be an efficient catalyst for the hydrogenation of arene derivatives under biphasic conditions. The rhodium nanoparticles (2-2.5 nm) were synthesized by the reduction of RhCl3 x 3H2O with sodium borohydride and were stabilized by highly water-soluble N-alkyl-N-(2-hydroxyethyl)ammonium salts (HEA-Cn). These surfactant molecules were characterized by measurements of the surface tension and the aqueous dispersions with rhodium were observed by transmission electron cryomicroscopy. The catalytic system is efficient under ultramild conditions, namely room temperature and 1 atm H2 pressure. The aqueous phase which contains the protected rhodium(0) colloids can be reused without significant loss of activity. The microheterogeneous behavior of this catalytic system was confirmed on a mercury poisoning experiment.