Arene Hydrogenation with a Stabilised Aqueous Rhodium(0) Suspension: A Major Effect of the Surfactant Counter‐Anion

Abstract

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 RhCl 3 ¥ 3 H 2 O with sodium borohydride and were stabilised by highly watersoluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium salts (HEA16X, X Br, Cl, I, CH 3 SO 3 , BF 4 ). 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.

Nanoheterogeneous Catalytic Hydrogenation of Arenes: Evaluation of the Surfactant‐Stabilized Aqueous Ruthenium(0) Colloidal Suspension

“…The surfactant HEA16Cl was prepared as previously reported and was fully characterized. [10] Analytical Procedures TEM analysis: The transmission electronic microscopic studies were conducted using a Philips CM 12 transmission electron microscope at 100 keV (UMR CNRS 6026 -University of Rennes I). Samples were prepared by a dropwise addition of the stabilized ruthenium colloids in water onto a copper sample mesh covered with carbon.…”

“…Previously, we have described the easy synthesis of N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium salts HEA16X with X = Br, Cl, I, CH 3 SO 3 , BF 4 . [10] Among these compounds, the chloride salt HEA16Cl has largely been studied as a protective agent for rhodium and iridium particles for the hydrogenation of benzene derivatives. [11,12] To complete our investigation on the noble metal efficiency in aromatic ring hydrogenation, we report the original synthesis of ruthenium nanocatalysts in aqueous suspension and their size distribution.…”

“…Nevertheless, the catalytic efficiencies of these two metallic species are really different: significant TOFs have only been observed under hydrogen pressures with ruthenium species, whereas arene hydrogenations could be performed at 1 bar of H 2 with rhodium nanocatalysts. In similar catalytic conditions (room temperature, 30 bar H 2 , magnetic stirring), the hydrogenation of anisole was complete after 15 min (TOF = 1200 h À1 ) with rhodium nanoparticles as previously described [10] and 1.25 h (TOF = 223 h…”

Catalytic Applications of Metal Nanoparticles in Imidazolium Ionic Liquids

“…[6] For example, good capping ligands-which stabilize robust nanocrystals with very narrow size distributions-are almost inactive catalysts for the hydrogenation reactions; [7] in contrast, MNP-containing stabilizers that bind less strongly to the metal surface than other anions generate higher catalytic activity. [8] Quaternary ammonium salts are one of the most popular and investigated classes of stabilizing agents for soluble transition-metal nanoparticle catalysts. [4,[9][10][11] It is assumed that the stabilization in these cases is essentially due to the positive charge on the metal surface which is ultimately induced by the adsorption of the anions on to the coordinatively unsaturated, electron-deficient, and initially neutral metal surface, [12] similar to the classic, anion-based, DLVO (Dergaugin-Landau-VerweyOverbeek)-type Coulombic repulsion model.…”

Synthesis of supported metal nanoparticle catalysts using ligand assisted methods

“…Strategies to facilitate NPs separation include decantation by using biphasic systems, such as the biphasic system water/organic solvent [15][16][17] or the two-phase system with ionic liquids, 18-20 and filtration or centrifugation by the immobilization of NPs on organic or inorganic supports (magnetic decantation can be used with magnetic supports…”