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This paper presents an overview of the results obtained in the synthesis of metal or metal oxide nanoparticles using hydrocarbyl complexes as metal source. The main advantage of using such metal precursors is their easy decomposition that can be achieved in solution and mild conditions. This allows the control of the particles size, shape and surface state in order to reach a monodisperse assembly of particles having the desired property. The results are reported taking into account the nature of the metal as well as in some cases the stabilizing mode (polymers, ligands, ionic liquids). Some results obtained in the deposition of metal nanoparticles within the channels of templates such as alumina membranes and mesoporous silica through a classsical impregnation method are also reported. The last part concerns the preparation of metal nanoparticles supported on a porous support using a fluidized bed.

A family of N-heterocyclic carbene (NHC)-stabilized Ru nanoparticles has been synthesized by using various NHC ligands, including a chiral one. The surface reactivity of the so-obtained RuNHC nanoparticles has been explored after reacting them with CO with the aim to probe the nature and availability of surface metal sites. Hydrogenation catalytic tests were also performed with the RuNHC NPs stabilized by a chiral ligand in order to evaluate their ability in enantioselective catalysis.

Hydrogenation of nitroarenes is a catalytic reaction of high interest owing to the importance of the resulting anilines for the chemical industry. For this transformation, a huge number of catalysts based on different metals have been reported so far. However, the chemoselective reduction of the nitro group when other reducible functionalities are present in the nitroaromatic substrates remains a challenging goal, and significant effort has been devoted to the development of more selective catalysts. In this context, metal nanoparticles (MNPs) have emerged as a good alternative to molecular complexes, and much attention is currently paid to their synthesis in order to achieve efficient and selective nanocatalysts. Non-supported and supported nanoparticles have been used for this catalytic reaction, and among them, platinum nanoparticles (PtNPs) appear as promising catalysts, due to the fact that they combine a good activity in nitro reduction while keeping a certain degree of selectivity. Herein, the most recent advances related to the preparation and application of PtNPs as catalysts in the hydrogenation of nitroaromatics are reviewed.

Large faceted Pt particles prepared in solution were in situ observed by ETEM (Environmental Transmission Electron Microscopy) during oxidation - reduction cycles. Reversible shape transformations were observed with the increase or decrease of the ratio of (111) faces to (001) faces in H2and O2respectively, at pressures of a few mbars. Under Hydrogen, the shape is relatively close to the Wulff shape of an fcc crystal under vacuum, while under oxygen, the (001) faces extend and the (111) faces shrink due to a stronger adsorption of oxygen on the more open (100) faces. Going from hydrogen to oxygen, the surface energy anisotropy is inverted.

RuO2@SiO2nanomaterials are prepared using hybrid mesostructured silica (EtO)2P(O)(CH2)3SiO1.5/xSiO2(x= 9, 16) by anchoring the metal precursor [Ru(COD)(COT)] (COD is 1,3‐cyclooctadiene, COT is 1,3,5‐cyclooctatriene) inside the pores of the organized silica matrix through the phosphonate moieties. Following this task, the nanoparticles are fabricated by i) decomposing the metal precursor with hydrogen at room temperature in tetrahydrofuran to achieve ruthenium nanoparticles and ii) thermally treating the ruthenium particles in silica at 450 °C in air to fabricate RuO2. The materials containing Ru and RuO2nanoparticles are characterized by elemental analysis, transmission electron microscopy (TEM), X‐ray diffraction (XRD), nitrogen sorption measurements, and 31P and 13C NMR. The obtained RuO2@SiO2nanomaterials are evaluated as catalytic filters when deposited onto gas sensors for the preferential detection of propane in the multicomponent gas mixture propane/carbon monoxide/nitrogen dioxide.

The synthesis of shape controlled platinum nanoparticles has been investigated through an organometallic approach starting from the complex Pt2(dba)3and using a long alkyl chain amine, hexadecylamine (HDA), as stabilizer. The influence of the experimental parameters (reactive gas and solvent nature, stabilizer/metal ratio, reactants concentration, temperature) on the shape of the Pt nanoparticles has been studied. Various shaped platinum nanostructures such as isolated nanoparticles, dendrites or crystalline nanowires were obtained, depending on the reaction conditions. This method takes profit of the mild conditions of chemistry in solution and allows obtaining regular nanostructures, most of them being homogeneous in shape as well as in size (isolated nanoparticles) or diameter/length (nanowires). Transmission electron microscopy and wide‐angle X‐ray scattering were used as characterization techniques. Beside the Knight‐shift effect of platinum, NMR solution investigations clearly evidenced the coordination of the amine at the Pt particles surface and its mobility. This mobility, increased when H2is used as reactive gas for the precursor decomposition, favors the particles coalescence into nanowires. This phenomenon is also favored by the “soft” template character of the amine in particular in toluene solution.

Ruthenium nanoparticles have been prepared by hydrogenation of the complex Ru(COD)(COT) (COD = 1,5‐cyclooctadiene, COT = 1,3,5‐cyclooctatriene) in the presence of i) heavily fluorinated solid compounds as stabilizers (para‐bis(perfluorooctyl)benzene, 2,4,6‐tris(perfluorooctyl)aniline, and the non‐functionalized 11H,11H,12H,12H,13H,13H,14H,14H,15H,15H,16H, 16H‐perfluorohexacosane (C10F21‐(CH2)6‐C10F21)); and ii) the liquid 1H,1H,2H,2H‐perfluorodecylamine. The particles have been characterized by IR spectroscopy, elemental analysis, transmission electron microscopy (TEM), high‐resolution TEM, wide‐ and small‐angle X‐ray scattering (WAXS and SAXS), and scanning electron microscopy with a field‐emission gun (SEM‐FEG). TEM images indicate the presence of aggregated small nanoparticles with a regular mean size of ca. 3 nm. These nanoparticles display the hexagonal close‐packed structure of bulk ruthenium, as shown by WAXS analysis. HRTEM and SEM‐FEG analyses reveal the tendency of the particles to self‐assemble into superstructures (spheres) that can be more or less well defined depending on the fluorinated compound and/or the reaction conditions. This behavior has been confirmed in one case by SAXS measurements attesting the presence of small nanoparticles that are closely packed into clusters.

The decomposition of the organometallic ruthenium precursor [Ru(COD)(COT)] (COD = 1,5-cyclooctadiene; COT = 1,3,5-cyclooctatriene) in mild conditions (193 K, 3 bar H2) in n-pentane leads, in the presence of octylsilane (H3SiC8H17) as stabilizer (ligand), to the formation of nanoparticles of about 2.3 nm in diameter with a narrow size distribution as demonstrated by TEM observations. Infrared spectroscopy shows that all the υ(Si−H) bands disappeared and that some alkyl fragments remain grafted on the metallic surface. Both liquid and solid state ¹³C CP-MAS NMR could be successfully applied to characterize alkylsilane fragments grafted on the ruthenium nanoparticles' surface. Similar results were obtained by the two techniques. Although the signal corresponding to the carbons in α position was missing and the signal corresponding to the carbon in β position was strongly lowered, the signals corresponding to the other carbons were clearly identified. This may be the result of both the lack of surface homogeneity and the weak “knight shift” of ruthenium. To our knowledge, it is the first time that ruthenium nanoparticles stabilized by surface-grafted alkylsilane fragments are synthesized and fully characterized by electron microscopy as well as solid state ¹³C MAS NMR.

Nanoporous alumina membranes, loaded with palladium and ruthenium nanoparticles of various size, were used for gas phase hydrogenation of 1, 3‐butadiene and for oxidation of carbon monoxide, respectively. Those membranes contain 109‐ 1011pores per cm2, all running perpendicular to the surface. Membrane discs of 20 mm in diameter and only 60 μm thick, incorporated in a reactor in which the reactants can be pumped in a closed circuit through the pores, turned out to very actively catalyze hydrogenation of butadiene (Pd) and oxidation of CO (Ru). The activity of the Pd catalysts depends characteristically on the particles size, the gas flow, and of the educts ratio. As could be expected, larger particles are less active than smaller ones, whereas increasing gas flows in case of hydrogenation accelerates the reactions. Excessive hydrogen reduces selectivity with respect to the various butenes, but favours formation of butane.

Ruthenium nanoparticles included in alumina membranes have been prepared either by dihydrogen decomposition of the complex Ru(COD)(COT) (COD = 1, 5‐cyclooctadiene; COT = 1, 3, 5‐cyclooctatriene) to give pre‐prepared colloidal solutions which were further used to fill the pores of nanoporous alumina membranes by vacuum induction, or by in situdecomposition. These hybrid systems were tested in the hydrogenation of 1, 3‐butadiene in the gas phase. The use of Ruthenium loaded membranes resulted in considerably increased activities compared with grinded samples.

Using a two-step procedure based on (i) anchoring an organogold precursor within the channels of functionalized ordered mesoporous silica containing mercapto groups; (ii) followed by chemical reduction, we prepared materials containing gold (0) nanoparticles exclusively located within the pore channels. By modifying the organogold precursor/mercapto groups ratio, we demonstrate the necessity of the complexation of the organogold precursor prior to reduction. Using this methodology, gold content as high as 16.1 wt % with a narrow size distribution of nanoparticles regularly distributed within the pores of the material was achieved.

Ruthenium nanoparticles of controlled size have been prepared by decomposition of the organometallic precursor Ru(cod)(cot) (cod = 1,5‐cyclooctadiene, cot = 1,3,5‐cyclooctatriene) under an H2atmosphere in either a pure alcohol or an alcohol/THF mixture as solvent and in the absence of further stabilizer. The particles were characterized by transmission electron microscopy (TEM), high‐resolution electron microscopy (HREM), X‐ray diffraction (XRD), wide‐angle X‐ray scattering (WAXS), and X‐ray photoelectron spectroscopy (XPS). The colloidal solutions are stable for long periods of time, in some cases longer than one year. TEM images reveal in most cases the presence of polycrystalline sponge‐like particles of regular spherical shape and homogeneous size or, in some cases, the presence of isolated and well‐dispersed monocrystalline particles, depending upon the alkyl chain length of the alcohol used. In all cases the size distributions are relatively narrow. WAXS and XRD analyses indicate the exclusive presence of hexagonal close‐packed (hcp) ruthenium in these materials. The size of the particles can be controlled by adjusting the reaction temperature or the composition of the solvent mixture. In case of MeOH/THF mixtures, a linear correlation was established between the solvent composition and the size of the particles in the range of 4–85 nm. In the absence of stirring, small individual monocrystalline Ru particles are formed inside superstructures that assemble in some cases into monolayers. Finally, these materials are promising in catalytic hydrogenation of arenes under mild conditions.

The reaction of Pt(dba)2 with Ru(COD)(COT) in various proportions under dihydrogen in the presence of PVP leads to the formation of bimetallic nanoparticles of definite compositions resulting from the relative concentration of the two complexes in the initial solution. The progressive incorporation of ruthenium into the platinum matrix leads to structural changes from face-centered cubic (fcc) for high platinum contents to hexagonal close-packed (hcp) for high ruthenium contents. For the composition Pt1Ru3 a contraction of the size of the particles (ca. 1.1 nm) and of the size distribution indicates the presence of a new phase consisting of monodisperse particles for which a model of truncated twinned octahedrons of 79 atoms was proposed.

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