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In the last fifteen-years, the application of metal nanoparticles as catalysts in organic synthesis has received a renewed interest. Therefore, much attention is currently being paid to the synthesis of metal nanoparticles in order to achieve the control of their characteristics in terms of size, shape and surface chemistry. Besides this, the recyclability as well as the recovery from the reaction medium still remain the major drawbacks to widespread the use of nanoparticles in catalysis. To overcome these problems, the immobilization of metal nanoparticles on solid supports appears as a promising alternative. In that context, carbon materials offer several advantages as solid supports such as availability, relatively low cost, high mechanical strength, chemical stability, and a pore structure along with an attractive surface chemistry which allows easy modifications, such as its functionalization, to suit the nanoparticles immobilization needs. Among the transition metals Palladium and Ruthenium are widely employed as efficient catalysts in many reactions. Herein, the most recent advances, from recent papers and patents, in relation to the preparation of carbon-supported Pd or Ru nanoparticles systems as well as their application as catalysts in alcohol oxidation, cross-coupling or hydrogenation reactions, are reviewed.

Suspensions of small sized (1-2.5 nm) ruthenium nanoparticles (RuNPs) have been obtained by decomposition, under H(2), of (η(4)-1,5-cyclooctadiene)(η(6)-1,3,5-cyclooctatriene)ruthenium(0), [Ru(COD)(COT)], in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(1)C(4)Im][NTf(2)], and in the presence of different compounds acting as ligands: C(8)H(17)NH(2), PPhH(2), PPh(2)H and H(2)O. Previous and new liquid NMR experiments showed that the ligands are coordinated or in the proximity to the surface of the RuNPs. Herein is reported how the ligand affects the catalytic performance (activity and selectivity) compared to a ligand-free system of RuNPs, when RuNPs in [C(1)C(4)Im][NTf(2)] are used as catalysts for the hydrogenation of various unsaturated compounds (1,3-cyclohexadiene, limonene and styrene). It has been observed that σ-donor ligands increase the activity of the nanoparticles, contrarily to π-acceptor ones.

We report in this paper the stabilization of ruthenium nanoparticles using a very simple ligand (4-(3-phenylpropyl)pyridine), through strong pi-coordination of the phenyl moiety.

Abstract: The organometallic synthesis of ruthenium nanoparticles stabilized by water-soluble alkyl sulfonated diphosphines as ligands is described for the first time. After isolation, the so-obtained nanoparticles could be easily dispersed into water giving rise to stable aqueous colloidal solutions without precipitation over the course of several months. The catalytic behaviour of these aqueous colloidal solutions has been investigated in the hydrogenation of unsaturated substrates (tetradecene, styrene and acetophenone) in biphasic liquid–liquid conditions, showing interesting results in terms of reactivity. Interestingly, small structural differences in the backbone of the diphosphine ligands influence the catalytic activity of these nanocatalysts. In addition, preliminary tests of recycling showed promising results with neither loss of activity or significant precipitation. [Copyright &y& Elsevier]

Abstract: This study reports an efficient method for the preparation of well-dispersed ruthenium nanoparticles of controlled size loaded into micelle-templated silica (MTS). This method is based on an organometallic approach consisting in mild decomposition of Ru(COD)(COT) (COD=η4-cycloocta-1,5-diene; COT=η6-cycloocta-1,3,5-triene) embedded inside mesostructured porous silica. The role assigned to the regular channels of MTS is to host and stabilize the metal nanoparticles. Different procedures of precursor decomposition, variation of metal loadings and of MTS pore sizes were examined in order to identify the crucial parameters governing the location, size and dispersion of the nanoparticles. The composite materials were characterized using elemental analysis, thermal gravimetric analysis, X-ray diffraction, nitrogen sorption at 77K and TEM. The advantage of this new procedure lies in the absence of particles sintering due to the Ru reduction at room temperature and the stabilization of the nanoparticles by suitable pore size of the host. [Copyright &y& Elsevier]