Poly(2-vinylpyridine) Grafted Silica Containing Palladium Nanoparticles: Synthesis, Characterization, and Catalytic Application in Carbon-Carbon Coupling Reactions

In this study poly(2-vinylpyridine) grafted silica-containing palladium nanoparticle as a heterogeneous and efficient catalytic system is introduced. Initially, acrylamidopropylsilica was prepared with the reaction of aminopropylsilica and acryloyl chloride and then 2-vinylpyridine monomer was grafted onto this functionalized silica by free radical polymerization. Finally, the catalyst was synthesized from the reaction of this polymeric matrix with palladium chloride and subsequent reduction with sodium borohydride. The system was characterized well through various techniques. The presence of functional groups was revealed with FT-IR spectroscopy, the amount of poly(2-vinylpyridine) grafted silica was determined by ThermoGravimetric Analysis (TGA), the amount of palladium on the polymeric matrix was obtained with ICP, Scanning Electron Microscopy (SEM) displayed catalyst morphology,  X-ray Photoelectron Spectroscopy (XPS) exhibited the presence of Pd(0) and Transmission Electron Microscopy (TEM) images showed that palladium dispersed through polymer surface in nanoparticle size without any agglomeration. This catalytic system exhibited excellent activity in C-C cross-coupling reactions of aryl iodides, bromides, and also chlorides, with olefinic compounds in Heck-Mizoraki, and with benzylbronic acid in Suzuki-Miyaura reactions. The catalyst was recycled and reused up to seven times in the Heck and Suzuki coupling reaction without considerable loss of activity. Short reaction time along with high yields and easy separation and purification of products from the reaction mixture are among the other advantages of this catalytic system.