Metal nanoparticles have been used for a long time to catalyze chemical reactions in both heterogeneous and homogeneous phases.[1] The analysis of traditional heterogeneous and homogeneous catalysis requires very different techniques that are difficult to combine for the study of metal nanoparticles, in which distinguishing between colloidal and molecular catalysis is difficult.[2] Thus, many questions concerning the reactivity of metal nanoparticles are still open, particularly the nature of intermediate surface species, knowledge of which is important for the development of new nanocatalysts and new catalytic transformations. Some of us have used solid-state NMR spectroscopy for this purpose recently, [3] and herein we report the combination of this method with desorption techniques for investigating the reactivity of ruthenium nanoparticles.The synthesis of metal nanoparticles by hydrogenation of organometallic precursors in the presence of organic ancillary ligands, such as amines, thiols, or carboxylic acids as stabilizers, has been investigated for over fifteen years by some of us.[4] In particular, essentially monodisperse, very small ruthenium nanoparticles, which display a remarkable surface coordination chemistry, can be obtained using [Ru-(cod)(cot)] as a precursor (cod = 1,5-cyclooctadiene; cot = 1,3,5-cyclooctatriene). This system, and similar ones involving Pd, Pt, or Rh nanoparticles, catalyzes a number of chemical reactions such as olefin hydrogenation, CÀC coupling, and hydrogenation of aromatic hydrocarbons.[5] Some of us have shown independently that palladium nanoparticles stabilized by asymmetric phosphite groups are good enantioselective alkylation catalysts.[6] This result provides strong evidence for the direct coordination of ligands, in this case phosphite groups, to the palladium surface.The coordination of ligands such as CO, [7] amines, [8] and organosilanes, [9] has previously been established by NMR spectroscopy studies in solution or in the solid state. The coordination of hydrogen to metal nanoparticles, however, is especially important. Hydrogen binding to clean metal surfaces has been well established by surface science, and it is generally accepted that one hydrogen atom is adsorbed per surface metal atom. [10] We have recently demonstrated the presence of mobile hydrides, which are in slow exchange with gaseous dihydrogen, on the surface of amine-protected ruthenium nanoparticles using a combination of gas-phase 1 H NMR and solid-state 2 H NMR spectroscopy. [3] Furthermore, other species, such as alkenes or arenes, may adsorb on the surface during a catalytic process or give rise to new reactive intermediates, including alkyl groups and carbenes. The important question which then arises is whether these groups are stable and can be detected spectroscopically, as in organometallic complexes.Herein we describe: 1) the synthesis of a new class of phosphine-protected ruthenium nanoparticles, 2) the characterization of phosphine coordination by NMR spectroscopy techniques, 3) the p...

This review provides a synthetic overview of the recent research advancements addressing the topic of catalysis with colloidal ruthenium metal nanoparticles through the last five years. The aim is to enlighten the interest of ruthenium metal at the nanoscale for a selection of catalytic reactions performed in solution condition. The recent progress in nanochemistry allowed providing well-controlled ruthenium nanoparticles which served as models and allowed study of how their characteristics influence their catalytic properties. Although this parameter is not enough often taken into consideration the surface chemistry of ruthenium nanoparticles starts to be better understood. This offers thus a strong basis to better apprehend catalytic processes on the metal surface and also explore how these can be affected by the stabilizing molecules as well as the ruthenium crystallographic structure. Ruthenium nanoparticles have been reported for their application as catalysts in solution for diverse reactions. The main ones are reduction, oxidation, Fischer–Tropsch, C–H activation, CO2 transformation, and hydrogen production through amine borane dehydrogenation or water-splitting reactions, which will be reviewed here. Results obtained showed that ruthenium nanoparticles can be highly performant in these reactions, but efforts are still required in order to be able to rationalize the results. Beside their catalytic performance, ruthenium nanocatalysts are very good models in order to investigate key parameters for a better controlled nanocatalysis. This is a challenging but fundamental task in order to develop more efficient catalytic systems, namely more active and more selective catalysts able to work in mild conditions.