Ruthenium and rhodium nanoparticles (MNP) were prepared in the presence of phosphine ligands containing fluorinated groups, starting from well-defined organometallic compounds. The syntheses of these new materials evidenced the crucial tuning between metal precursor and ligand. These nanocatalysts were used in hydrogenation reactions of arene derivatives in organic solvent (THF) and supercritical carbon dioxide (scCO(2)). The catalytic behaviour observed (activity and selectivity) showed that both Ru and Rh systems are less active in scCO(2) than in THF, preventing the hydrogenation of the aromatic group when electron-donor groups (like ether moieties) are present on the substrate. (C) 2009 Elsevier B.V. All rights reserved.