Palladium Nanoparticles Stabilized by Glycodendrimers and Their Application in Catalysis

Palladium nanoparticles stabilized by glycodendrimers (PdDSNs) in water were prepared by coordination of Pd-II to intradendritic triazole ligands upon reaction of K2PdCl4 with the dendrimer in water followed by aqueous NaBH4 reduction to Pd-0. TEM images show that the PdDSNs are small (average diameter: 2.3 nm) and relatively monodisperse owing to a low concentration of metal precursor. The catalytic activity of these PdDSNs was evaluated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 (only 0.2 mol-% of Pd per mol substrate is used) and for the Miyaura-Suzuki C-C coupling with various substituted aryl bromides (only 0.01 mol-% of Pd per mol substrate is used). Comparisons of the catalytic activities of these PdDSNs with those of larger PdDSNs (diameter: 14 nm) reveal that smaller NPs catalyze faster 4-NP reduction than their larger counterparts but lack any notable surface dependency for Suzuki-Miyaura catalysis.