Selective hydrogenation and/or isomerization of olefins are important processes in both chemical and pharmaceutical industries. Our group previously reported that the thiosulfate protocol using sodium S-alkylthiosulfates instead of alkanethiols could generate catalytically active Pd nanoparticles (PdNPs) capped with a lower density of alkanethiolate ligands. PdNPs were characterized by thermogravimetric analysis (TGA), proton NMR, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), IR and UV-vis spectroscopy, and gas adsorption using the Brunauer-Emmett-Teller (BET) model. These unsupported colloidal PdNP catalysts exhibit an excellent selectivity toward the isomerization of allylic alcohols to carbonyls in organic solvents. PdNPs are also found to have high selectivities for the isomerization of terminal alkenes to internal alkenes and the mono-hydrogenation of dienes and trienes. High chemoselectivity for the hydrogenation of olefins in the presence of other reactive functional groups such as nitro, halo, nitrile, imine, and carbonyl groups is observed for the partially poisoned colloidal nanoparticles. The high activity of colloidal Pd nanoparticle catalysts allows the reactions to be completed under mild conditions, at atmospheric pressure and room temperature. In addition, these homogeneously soluble PdNP catalysts offer an advantage of facile separation and multiple recycling without significant losses in activity and selectivity. The strong influence of thiolate poisoning ligands on the chemical and electronic properties of the Pd surface is observed from various catalysis results. The further systematic evaluation of metal nanoparticle catalysts functionalized with well-defined small thiolate ligands would provide important fundamental understandings on the influence of chemical environments near active sites and pave a way to develop chemo-, regio-, and stereo-selective colloidal nanoparticle catalysts.

Partially poisoned Pd nanoparticles for selective hydrogenation and/or isomerization of olefins

256th National Meeting (2018)

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