Ligand-stabilized ruthenium nanoparticles: Synthesis, organization, and dynamics

The decomposition of the ruthenium precursor Ru(COD)(COT) (1, COD = 1,5-cyc looctadiene; COT = 1,3,5-cyclooctatriene) in mild conditions (room temperat ure, 1-3 bar H-2) in THF leads, in the presence of a stabilizer (polymer or ligand), to nanoparticles of various sizes and shapes. In THF and in the p resence of a polymer matrix (Ru/polymer = 5%), crystalline hcp particles of uniform mean size (1.1 nm) homogeneously dispersed in the polymer matrix a nd agglomerated hcp particles (1.7 nm) were respectively obtained in poly(v inylpyrrolidone) and cellulose acetate. The same reaction, carried out usin g various concentrations relative to ruthenium of alkylamines or alkylthiol s as stabilizers (L = C8H17NH2, C12H25NH2, C16H33NH2, C8H17SH, C12H25SH, or C16H33SH), leads to agglomerated particles (L = thiol) or particles disper sed in the solution (L amine), both displaying a mean size near 2-3 nm and an hcp structure. In the case of amine ligands, the particles are generally elongated and display a tendency to form worm- or rodlike structures at hi gh amine concentration. This phenomenon is attributed to a rapid amine liga nd exchange at the surface of the particle as observed by C-13 NMR. In cont rast, the particles stabilized by C8H17SH are not fluxional, but a catalyti c transformation of thiols into disulfides has been observed which involves oxidative addition of thiols on the ruthenium surface. All colloids were c haracterized by microanalysis, infrared spectroscopy after CO adsorption, h igh-resolution electron microscopy, and wide-angle X-ray scattering.