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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.

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.

The morphology of platinum nanoparticles synthesized using an organometallic approach from PtMe(2) (C(8) H(12) ) is influenced by the nature of the ligands used as stabilizing agents. The use of long alkyl chain amines leads to the formation of multipodal nanoparticles that transform into compact nano-objects, adopting cubic, truncated cubic, or cuboctahedral shapes. In contrast, the use of diamine ligands allows the growth of compact (111) arrowlike faces, forming polycrystalline nanoparticles of an overall desert-rose aspect. Different reaction parameters are studied ([ligand]/[metal] ratio, temperature, solvent identity) in order to optimize the various shapes., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Metallic Ru, Rh, and Ir nanoparticles were prepared by the decomposition of organometallic precursors under H(2) pressure in the presence of 1,3-diphosphite ligands, derived from carbohydrates, as stabilizing agents. Structural modifications to the diphosphite backbone were found to influence the nanoparticles' size, dispersion, and catalytic activity. In the hydrogenation of o- and m-methylanisole, the Rh nanoparticles showed higher catalytic activity than the corresponding Ru nanoparticles. The Ir nanoparticles presented the lowest catalytic activity of the series. In all cases, the hydrogenation of o-methylanisole gave total selectivity for the cis-product, however, the ee of the product was always less than 6 %. A maximum of 81 % cis-selectivity was obtained for the hydrogenation of m-methylanisole, however, no asymmetric induction was observed. These results show that the catalytic activity is affected by a combination of influences from the substrate, the diphosphite ligands, and the metallic nanoparticles.

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.

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. [ABSTRACT FROM AUTHOR]

The reactivity of ruthenium nanoparticles stabilized by 4-(3-phenylpropyl)pyridine in hydrogen transfer and hydrogenation processes was monitored by NMR spectroscopy. Unsaturated substrates such as styrene, 4-vinylpyridine and 4-phenyl-but-3-en-2-one were used as model molecules to investigate the surface properties of nanoparticles by a combination of NMR studies. Interestingly, the hydrides present at the metallic surface after nanoparticles synthesis are selectively transferred to vinylic groups without reducing the aromatic rings, under dihydrogen-free atmosphere. DOSY and NOE NMR experiments permitted to propose a way of interaction of the organic compounds at the metallic surface. In particular, the coordination of the substrate could be evidenced for 4-vinylpyridine and 4-ethylpyridine but not for styrene derivatives. Graphical Abstract: Curved double arrows represent magnetization exchanges. Straight arrows represent adsorption/desorption phenomena. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Composition (metal or metal oxide core and organic coating), size, shape and structure are the main parameters governing the properties of nano-objects. Driven by their huge potential for application in fields as diverse as catalysis, energy, environment, electronics and medicine much research effort has been dedicated to the control of these parameters over the past 30 years. Namely, the use of concepts and techniques of molecular chemistry has provided remarkable advances in the growth of well-defined nanostructures by pointing out the key roles played by both the metal precursors and stabilizing agents (polymers, dendrimers, ionic liquids, ligands, etc .) during the three main steps of the formation of nanostructures: release of metal atoms, nucleation and growth. It is now currently admitted that interaction between the precursor and stabilizing agent may generate intermediate complexes in the reacting medium which may change the course of the reaction. Also, coordination of the ligand on the growing seeds is recognized as an important factor influencing the growth of nanostructures. Finally, coordination of the ligand at the surface of nanostructures may induce a change in their physical and chemical properties by tuning electronic density and steric hindrance at their surface. To illustrate these points, this review will focus on metal nanostructures synthesized in organic solutions from molecular metal complexes as metal sources and stabilized by coating ligands, short chain molecules with headgroups able to coordinate onto the metal surface. Recent advances will be described highlighting the incidence of coordination chemistry through a selection of relevant examples from the literature. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalysts based on carbon-supported Pd nanoparticles (NPs) were prepared. [•] Catalysts activity was investigated in the hydrogenation of anthracene. [•] High conversions and selectivities towards the hydrogenated products were achieved. [•] No cracking or ring-opening products were obtained. [•] Reaction pathway for anthracene hydrogenation is proposed. [Copyright &y& Elsevier]

Review: 313 refs. [ABSTRACT FROM AUTHOR]

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]