In the prior studies from our research group, stable and isolable palladium nanoparticles (PdNPs) were synthesized by employing sodium S-dodecylthiosulfate ligand precursors. Interestingly enough, this methodology yielded dodecanethiolate-capped PdNPs with overall lower ligand surface coverage after the cleavage of the SO3 moiety during the passivation of growing PdNPs. Such PdNPs were capable of catalyzing a wide array of organic reactions due to the high accessibility of substrates to the reactive Pd surface.In this study, the effects of the structure of thiolate ligands on catalytic activity and selectivity of PdNPs are investigated, because the different structures (linear vs aromatic vs cyclohexyl) of surface-immobilized ligands should have interesting effects on the catalytic properties of PdNPs by altering the accessibility of substrates to the surface of nanoparticles and influencing ligand-substrate interactions.First, the distinct thiosulfate ligand precursors (sodium S-hexylthiosulfate, sodium S-cyclohexylethylthiosulfate, and sodium S-phenylethylthiosulfate) are synthesized from their alkyl halide counterparts by simple nucleophilic substitution reactions. Second, PdNPs capped with these ligands are synthesized using the methodology developed in our lab, which is a modification of the Brust-Schiffrin reaction. Systematic variations such as the reactant equivalents of tetra-n-octylammonium bromide (phase transfer agent), sodium boron hydride (reducing agent), and/or sodium S-alkylthiosulfate are attempted to control the core size and surface ligand density of these PdNPs. PdNPs are then characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), FT-IR, UV-Vis, and 1H NMR spectroscopy. Moreover, the catalytic activity and selectivity of PdNPs with three different types of surface-immobilized ligands are compared by analyzing the results obtained from the hydrogenation and/or isomerization of allyl alcohols.

Controlling activity of ligand-capped Pd nanoparticle catalysts: Effects of thiolate ligand structure

248th National Meeting (2014)

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