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Production of hydrogen from a renewable source that is water requires the development of sustainable catalytic processes. This implies, among others, developing efficient catalytic materials from abundant and low-cost resources and investigating their performance, especially in the oxidation of water as this half-reaction is the bottleneck of the water splitting process. For this purpose, NiFe-based nanoparticles with sizes ca . 3-4 nm have been synthesized by an organometallic approach and characterized by complementary techniques (WAXS, TEM, STEM-HAADF, EDX, XPS, and ATR-FTIR). They display a Ni core and a mixed Ni-Fe oxide shell. Once deposited onto FTO electrodes, they have been assessed in the electrocatalytic oxygen evolution reaction under alkaline conditions. Three different Ni/Fe ratios (2/1, 1/1 and 1/9) have been studied in comparison with their monometallic counterparts. The Ni2Fe1 nanocatalyst displayed the lowest overpotential (320 mV at j = 10 mA cm -2 ) as well as excellent stability over 16 h.

The electrochemical reduction of organic contaminants allows their removal from water. In this contribution, the electrocatalytic hydrogenation of nitrobenzene is studied using both oxidized carbon fibres and ruthenium nanoparticles supported on unmodified carbon fibres as catalysts. The two systems produce azoxynitrobenzene as the main product, while aniline is only observed in minor quantities. Although PhNO2 hydrogenation is the favoured reaction, the hydrogen evolution reaction (HER) competes in both systems under catalytic conditions. H2 formation occurs in larger amounts when using the Ru nanoparticle based catalyst. While similar reaction outputs were observed for both catalytic systems, DFT calculations revealed some significant differences related to distinct interactions between the catalytic material and the organic substrates or products, which could pave the way for the design of new catalytic materials.

A series of ferrocenylphosphine-stabilized rhodium nanoparticles has been prepared in one pot from the organometallic [Rh(η3-C3H5)3] precursor. This complex has been decomposed by hydrogen treatment (3 bar) in dichloromethane in the presence of five different ferrocene-based phosphine ligands. Very small rhodium nanoparticles in the size range of 1.1-1.7 nm have been obtained. These nanoparticles have shown activity in a model catalytic reaction, namely the hydrogenation of styrene. These results evidence that the metal surface is not blocked despite the steric bulk of the stabilizing ligands. Moreover, certain selectivity has been observed depending on the ligand employed. To the best of our knowledge, such a type of compound has not yet been used for stabilizing metal nanoparticles and our findings highlight the interest to do so.

The choice of suitable organometallic precursors, [Re 2 (C 3 H 5 ) 4 ] and [Ru(Me-Allyl) 2 COD] or [Ru(COD)(COT)], allows us to synthesize polyvinylpyrrolidone (PVP) stabilized bimetallic RuRe nanoparticles of ca. 1.3 nm with narrow size dispersity, displaying the hcp crystal structure and to control their chemical order: an alloy or Re rich surface. The structural features of these NPs were determined using complementary characterization techniques (TEM, HRTEM, STEM-HAADF, EDX, WAXS, FT-IR, MAS-NMR and ICP). In particular, surface state investigation based on CO adsorption and oxidation reactions provided useful information of the chemical order in these nanoparticles. The RuRe NPs were obtained as stable colloidal solutions or powders. Surface reactivity studies demonstrated that the alloy type RuRe/PVP NPs show better resistance to oxidation than the ones displaying a Re enriched surface and are more active towards CO dissociation than monometallic Re/PVP NPs as a result of the synergic effect between Ru and Re. Interestingly, the dissociation of CO was not observed with RuRe/PVP NPs displaying a Re enriched surface. Besides the synthetic aspect, this work highlights the crucial influence of the chemical order resulting from the choice of the metal sources in the control of the reactivity of ultra-small metal nanoparticles.

Herein we report a one pot organometallic strategy to access alumina-embedded Pd nanoparticles. Unexpectedly, the decomposition of the organometallic complex tris(dibenzylideneacetone)dipalladium(0), Pd 2 (dba) 3 , by dihydrogen in the presence of aluminum isopropoxide, Al(iPrO) 3 , and without extra stabilizers, was found to be an efficient method to generate a Pd colloidal solution. Careful characterization studies revealed that the so-obtained Pd nanoparticles were stabilized by an aluminum isopropoxide tetramer and 1,5-diphenyl-pentan-3-one, which was produced after reduction of the dba ligand from the organometallic precursor. Moreover, calcination of the obtained nanomaterial in air at 773 K for 2 h resulted in a nanocomposite material containing Pd nanoparticles embedded in Al 2 O 3 . This stabilization strategy opens new possibilities for the preparation of transition metal nanoparticles embedded in oxides.

In this work, we describe the synthesis of a new N-heterocyclic carbene (NHC) ligand, derived from a hybrid pyrazole-imidazolium scaffold, namely 1-[2-(3,5-dimethylpyrazol-1-yl)ethyl]-3-((S)-1-phenylethyl)-3H-imidazol-2-ylidene (L). This ligand has been used as a stabilizer for the organometallic synthesis of palladium(0) nanoparticles (Pd NPs). L presents a better stabilizing effect than its pre-carbenic HLCl counterpart, allowing the formation of isolated Pd NPs while HLCl yields aggregated ones. Additionally, molecular Pd(ii) coordination compounds of L and HLCl were synthesized and characterized to better understand the coordination modes of these ligands. Both molecular and colloidal Pd systems have been further tested in catalytic C-C coupling processes. Three different types of reactions have been observed depending on the catalytic system: (i) the Suzuki-Miyaura reaction takes place with Pd molecular complexes; (ii) a secondary reaction, the dehalogenation of the substrate, is always detected and (iii) the C-C homocoupling between two molecules of bromoarenes is observed with colloidal catalysts.

A series of Ni(0) nanocatalysts was prepared from a Ni(COD) 2 complex in the presence of different stabilizers (hexadecylamine, polyvinylpyrrolidone (PVP), PVP/triphenylphosphine, octanoic acid and stearic acid) for their evaluation in the selective hydrogenation reaction of α,β-unsaturated carbonyl compounds by H 2 under mild reaction conditions, i.e., low H 2 pressure, temperature and catalyst loading. All nanocatalysts were active in reducing only the C[double bond, length as m-dash]C bond and this chemoselectivity was attributed to the reduced nature of the Ni-NPs surface. Moreover, the hydrogenation reaction rate appeared to be sensitive to ligand type, with the carboxylic acid-stabilized systems showing the best performances. A full kinetic investigation into the t-chalcone chemoselective reduction of the C[double bond, length as m-dash]C bond, with the best catalyst (Ni-octanoic acid) revealed that the rate-determining step is the hydrogenation of the adsorbed substrate on the NPs surface, following a Horiuti-Polanyi type of mechanism. Regarding sustainable chemistry concerns, the best catalyst could be reused up to 10 times without significant loss of activity.

Polyvinylpyrrolidone-stabilized Rh nanoparticles (RhNPs/PVP) of ca. 2.2 nm in size were prepared by the hydrogenation of the organometallic complex [Rh(η 3 -C 3 H 5 ) 3 ] in the presence of PVP and evaluated as a catalyst in the hydrogenation of a series of arene substrates as well as levulinic acid and methyl levulinate. The catalyst showed excellent activity and selectivity towards aromatic ring hydrogenation compared to other reported transition metal-based catalysts under mild reaction conditions (room temperature and 1 bar H 2 ). Furthermore, it was shown to be a highly promising catalyst for the hydrogenation of levulinic acid and methyl levulinate in water leading to quantitative formation of the fuel additive γ-valerolactone under moderate reaction conditions compared to previously reported catalytic systems.

The solution synthesis of rhodium nanoparticles (Rh NPs) was achieved from the organometallic complex [Rh(η 3 -C 3 H 5 ) 3 ] under mild reaction conditions in the presence of a polymer (PVP), a monophosphine (PPh 3 ) and a diphosphine (dppb) as a stabilizer, leading to very small Rh NPs of 2.2, 1.3 and 1.7 nm mean size, with PVP, PPh 3 and dppb, respectively. The surface properties of these nanoparticles were compared using a model catalysis reaction namely, hydrogenation of cyclohexene, first under colloidal conditions and then under supported conditions after their immobilization onto an amino functionalized silica-coated magnetite support. PVP-stabilized Rh NPs were the most active catalyst whatever the catalytic conditions as a result of a strong coordination of the phosphine ligands at the metal surface that blocks some surface atoms even after several recycles of the supported nanocatalysts and limit the reactivity of the metallic surface.

Core-shell RuPt (Ru core-Pt shell) and PtRu (Pt core-Ru shell) nanoparticles were prepared by decomposing in a two-step procedure a ruthenium ([Ru(COD)(COT)] (COD = 1,5-cyclooctadiene, COT = 1,3,5-cyclooctatriene)) and a platinum complex ([Pt2(dba)3] (dba = dibenzylideneacetone) or [Pt(CH3)2(COD)]) in the presence of 4-(3-phenylpropyl)pyridine (PPP) as a stabilizer and using different Ru/Pt ratios. The data obtained from a combination of several analyses (TEM, HRTEM, WAXS and IR) indicate that the so-obtained nanoparticles present a core-shell structure. The catalytic performances of these bimetallic nanoparticles for the selective hydrogenation of trans-cinnamaldehyde were investigated, which provided interesting results as well as useful information to elucidate their structure and composition. Indeed, the catalytic results evidence that: (1) the combination of both metals led in some cases to a synergistic effect on the selectivity of the reaction, and (2) the structure and the composition affected the selectivity of the reaction.

Diphenylphosphinobutane (dppb) stabilized bimetallic RuPt nanoparticles were prepared by co-decomposition of [Ru(COD)(COT)] [(1,5-cyclooctadiene)(1,3,5-cyclooctatriene)ruthenium] and [Pt(CH(3))(2)(COD)] [dimethyl(1,5-cyclooctadiene) platinum(II)] organometallic precursors under mild conditions (room temperature, 3 bar of dihydrogen) and in the presence of dppb. The determination of the nanoparticles' chemical composition was made possible thanks to a combination of several characterization techniques (HREM, STEM-HAADF, WAXS, EXAFS, IR, NMR) associated with surface reactivity studies based on simple catalytic reactions. The obtained nanoparticles display a ruthenium rich core and a disordered shell containing both ruthenium and platinum. The results were compared with those obtained on nanoparticles of similar size and composition but not containing ligands. The complexity observed in the present structure of these nanoparticles arises from the high chemical affinity of the diphosphine ligand used as a stabilizer for both metals.

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.

Dimethylamine-borane, (CH(3))(2)NHBH(3), has been considered as one of the attractive materials for the efficient storage of hydrogen, which is still one of the key issues in the "Hydrogen Economy". In a recent communication we have reported the synthesis and characterization of 3-aminopropyltriethoxysilane stabilized ruthenium(0) nanoparticles with the preliminary results for their catalytic performance in the dehydrogenation of dimethylamine-borane at room temperature. Herein, we report a complete work including (i) effect of initial [APTS]/[Ru] molar ratio on both the size and the catalytic activity of ruthenium(0) nanoparticles, (ii) collection of extensive kinetic data under non-MTL conditions depending on the substrate and catalyst concentrations to define the rate law of Ru(0)/APTS-catalyzed dehydrogenation of dimethylamine-borane at room temperature, (iii) determination of activation parameters (E(a), ΔH(#) and ΔS(#)) for Ru(0)/APTS-catalyzed dehydrogenation of dimethylamine-borane; (iv) demonstration of the catalytic lifetime of Ru(0)/APTS nanoparticles in the dehydrogenation of dimethylamine-borane at room temperature, (v) testing the bottlability and reusability of Ru(0)/APTS nanocatalyst in the room-temperature dehydrogenation of dimethylamine-borane, (vi) quantitative carbon disulfide (CS(2)) poisoning experiments to find a corrected TTO and TOF values on a per-active-ruthenium-atom basis, (vii) a summary of extensive literature review for the catalysts tested in the catalytic dehydrogenation of dimethylamine-borane as part of the results and discussions.

Very stable suspensions of small sized (c.a. 1.2 nm) and homogeneously dispersed ruthenium nanoparticles (RuNPs) were obtained by decomposition, under H(2), of (η(4)-1,5-cyclooctadiene)(η(6)-1,3,5-cyclooctatriene)ruthenium(0), [Ru(COD)(COT)], in various imidazolium derived ionic liquids (ILs: [RMIm][NTf(2)] (R = C(n)H(2n+1) where n = 2; 4; 6; 8; 10) and in the presence of amines as ligands (1-octylamine, 1-hexadecylamine). These nanoparticles were compared to others stabilized either in pure ILs or by the same ligands in THF. NMR experiments ((13)C solution and DOSY) demonstrate that the amines are coordinated to the surface of the RuNPs. These RuNPs were investigated for the hydrogenation of aromatics and have shown a high level of recyclability (up to 10 cycles) with neither loss of activity nor significant agglomeration.

An organometallic synthesis of ruthenium and platinum nanoparticles and their transfer into water using 1,3,5-triaza-7-phosphaadamantane as stabilizer is reported.

Structural and spectroscopic properties of tetranuclear ruthenium hydrido clusters, and to a less extent, of hexanuclear ruthenium hydrido clusters, are investigated theoretically. Some of these (H)(n)Ru(k)(L)(m) (k = 4, 6) clusters were experimentally synthesized and characterized. Non-existing structures are also considered in order to examine the role of ligands on their structure, vibrational spectra and (1)H NMR chemical shifts. The calculated properties are found in very good agreement with experimental data, when available. Beyond the intrinsic interest elicited by transition metal clusters, these compounds are also considered in this paper as relevant to diamagnetic ruthenium nanoparticles as well as building blocks of hcp surfaces, which is the ruthenium nanoparticle lattice. On the basis of the very good agreement between experiments and theory, the structural and spectroscopic properties of several model clusters are also predicted in order to bring additional data which may help to analyze the spectral signature of ruthenium nanoparticles. A particular emphasis is put on (1)H NMR, which is of high practical importance for characterizing the presence of hydrides in ruthenium clusters and nanoparticles. Several topics are discussed: the structural preference of surface hydrides for terminal-, edge-bridging or face-capping coordination modes, hydrides adsorption energies, the possible presence of interstitial hydrogen atoms, the dependence of (1)H chemical shifts on ligands and on electron counting.