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Abstract
A facile and efficient method was developed for the synthesis of highly active palladium nanoparticles (PdNPs) by microwave-assisted chemical reduction. The PdNPs with different morphology were prepared with or without KBr (capping agent) using ethylene glycol (EG) and citric acid (CA) as reducing agent in the presence of polyvinylpyrrolidone (PVP), respectively. The as-prepared PdNPs were characterized by (UV-Visible Spectrophotometer) UV-Vis, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The results showed that the PdNPs reduced by EG without KBr (PdNPs-EG) has smaller particle size than other PdNPs. The remarkable catalytic activity of the PdNPs catalysts are obtained using a low amount of PdNPs (0.1 mmol‰) using K2CO3 as base and EtOH/H2O as solvent toward Suzuki coupling reactions of aryl bromides and phenylboronic acid for 15 min.
Highlights
The Suzuki coupling reactions catalyzed by the transition metal palladium are very powerful tools for the construction of C-C bonds since its discovery in 1979 [1]
The yield of 99.3%, 98.8%, 97.8% and 98.2% are obtained for the Suzuki coupling reaction of 4-bromoacetophenone with phenylboronic acid catalyzed by Pd nanoparticles (PdNPs)-ethylene glycol (EG), PdNPs-KBrEG, PdNPs-citric acid (CA) and PdNPs-KBr-CA, respectively (Table 2, entry 4)
The PdNPs with small particle size and high degree of dispersion protected by PVP have been prepared using ethylene glycol (EG) and citric acid (CA) as reducing agent, PVP as protecting agent by microwaveassisted chemical reduction
Summary
The Suzuki coupling reactions catalyzed by the transition metal palladium are very powerful tools for the construction of C-C bonds since its discovery in 1979 [1]. The palladium-based catalysts are considered as the most available coupling catalysts, numerous efforts have been conducted to explore highly active catalytic systems [7]. The homogenous Pd catalysts with ligand generally exhibited higher catalytic activity and have been most frequently applied in Suzuki coupling reactions [8]. Pd nanoparticles (PdNPs) with high surface-to-volume ratio and highly active surface atoms in comparison with those of the bulk catalysts exhibit excellent activity [16] and have attracted great interest. Numerous efforts have been made to develop effective and facile synthetic method to prepare well-defined and uniform-sized metal nanoparticles [17]. The metal nanoparticles prepared by MWI have nanometer size with narrow size distribution [18 - 21]
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