Organometallic Ruthenium Nanoparticles: A Comparative Study of the Influence of the Stabilizer on their Characteristics and Reactivity

The use of metal nanoparticles as catalysts is a topic of growing interest at the frontier between homogeneous and heterogeneous catalysis. Metal nanoparticles are highly interesting systems owing to their high number of surface atoms, which give rise to numerous active sites. Furthermore, the surface properties of metal nanoparticles can be tuned by the addition of a stabilizer, for example, a polymer, a surfactant, or a ligand, or by combining a metal with a support to take profit of their synergy to orientate a catalytic reaction. Significant efforts are being made towards the synthesis of metal nanoparticles in general and, more precisely, towards the preparation of ligand-stabilized nanoparticles in which the size, shape, and surface state are controlled. Since ligands can modulate both the electronic and steric environment at the surface of the particles, numerous studies are presently devoted to analyze the influence of ligands on the stabilization of nanoparticles and on their surface properties. Such studies are of key importance to develop more active and selective nanocatalysts. In that context, ruthenium nanoparticles are candidates of choice as they can be characterized inter alia by nuclear magnetic resonance, as ruthenium displays little or no Knight shift and since they are active catalysts for hydrogenation reactions of, for example, arenes, olefins, and alkynes. In this Review, we present an overview of our group's efforts in the synthesis of ligand-stabilized ruthenium nanoparticles of controlled size and surface state using different types of ligands. We report the influence of nitrogen-, sulfur-, silicon-, phosphorus-and carbon-containing ligands as coordinating atoms to the metal surface, on their stabilization, as well as on their surface reactivity, in comparison with sterically-stabilized Ru nanoparticles prepared following the same organometallic approach, but using polymers or nanoreactors made of alcohols or ionic liquids that allow for control of the growth of the particles by a confinement effect. Nanoparticles of other metals are also described when appropriate.