Stabilized Rhodium(0) Nanoparticles: A Reusable Hydrogenation Catalyst for Arene Derivatives in a Biphasic Water-Liquid System

Abstract

A colloidal system based on an aqueous suspension of rhodium(0) 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 RhCl 3´3 H 2 O with sodium borohydride and were stabilized by highly watersoluble N-alkyl-N-(2-hydroxyethyl)ammonium salts (HEA-C n ). 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 H 2 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.

Aqueous‐Phase Fischer–Tropsch Synthesis with a Ruthenium Nanocluster Catalyst

“…Supported and unsupported catalysts have been widely investigated over the last 80 years or more, [2] and it is unlikely that further major improvements in the economic and energy efficiencies of the process can be realized with conventional catalysts. It has been reported that soluble nanoclusters [3] in ionic liquids [4] or liquid water [5] exhibit excellent catalytic performance in the hydrogenation of various organic substrates and also are comparatively green in nature. It has been reported that soluble nanoclusters [3] in ionic liquids [4] or liquid water [5] exhibit excellent catalytic performance in the hydrogenation of various organic substrates and also are comparatively green in nature.…”

Odyssey in Polyphasic Catalysis by Metal Nanoparticles

“…Since 2000, more than one hundred compounds have been synthesized and evaluated as protective agents of metal nanospecies according to their modulations. From surface tension measurements, most of these ionic salts display a surfactant behavior, and self‐aggregate above the critical micellar concentration (cmc) 52,57–58. The ammonium surfactants were efficiently used as capping agents of various transition metals (Ru, Rh, Pd, Ir, Pt, Au) in water.…”

“…Colloidal suspensions of Rh(0) were easily prepared by chemical reduction of rhodium trichloride, with sodium borohydride, in the presence of the ammonium stabilizer. An optimized [Surfactant]/[Rh] molar ratio of 2 proved to be relevant to avoid aggregation of the particles and to achieve significant catalytic activity 52. In the HEA series, in combination with the hydroxylated polar head, a C16 lipophilic chain provides the most suitable electrosteric stabilization 15.…”

“…The nanocatalysts were also easily reused, with no metal leaching, through an efficient biphasic recycling, the product being extracted with an organic solvent (Figure ). The use of surfactant‐capped Rh(0) colloids was extended to a large variety of arene derivatives (alkylated, functionalized and disubstituted aromatics),52,57–58 as well as to heteroaromatics 70. If necessary, an activation of the catalytic suspension could be achieved by an increase in hydrogen pressure 58.…”

A mild route to solid-supported rhodium nanoparticle catalysts and their application to the selective hydrogenation reaction of substituted arenes

“…Full conversion with 100% selectivity to methyl-cyclohexanecarboxylate (8a) required 60 °C and 10 bar H 2 . 75 On the other hand, low rates observed for EDG groups have been attributed to the higher energy barrier toward hydrogenation due to π-complexation of the aromatic ring. Ring deactivation effect and scarce resistance of ketonic group toward reduction was confirmed by the hydrogenation of 10 which provided cyclohexyl(phenyl)methanone (10a) in 1.3% yield under the above conditions.…”