Monodisperse thioether-stabilized palladium nanoparticles: Synthesis, characterization, and reactivity

Size control of monodisperse palladium nanoparticles with sizes ranging from 1.7 to 3.5 nm was accomplished using thioethers as stabilizing ligands, in a one-step procedure. Modulation of the reaction temperature, reaction time, solvent, and carbon chain length of the thioether provided control over the nanoparticle size and size distribution. The resulting Pd nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). H-1 NMR spectroscopy provided insight into the thioether-Pd nanoparticle surface interaction. To demonstrate the catalytic activity of the thioether-stabilized Pd nanoparticles, hydrogenation reactions were carried out using the as-synthesized Pd nanoparticles. We observed a trend in the reactivity of the nanoparticles with respect to their size, however, recovery of the nanoparticles following subsequent reactions was rather challenging. Immobilization of the Pd nanoparticles onto commercial SiO2 resulted in rapid and efficient catalysis, successful recovery of the Pd nanoparticles, and furthermore, the nanoparticles could be used up to 8 times with no measurable decrease in catalytic activity. This work demonstrates the utility of thioether ligands for the synthesis of monodisperse Pd nanoparticles that are efficient catalysts for various organic transformations.