Palladium@silica-coated magnetic nanoparticles as efficient and recyclable catalysts for ligand-free Suzuki-Miyaura coupling reaction under mild conditions

Many efforts have been done to develop new catalysts for organic reactions. In this study, preparation and characterization of palladium immobilized on modified magnetic Fe3O4 nanocatalyst (Fe3O4@SiO2@DPA-Pd) have been reported; dipicolylamine (DPA) groups are used as linkers to fix palladium nanoparticles on silica-coated Fe3O4 nanoparticles without agglomeration. The structure of the nanocatalyst was investigated using scanning electron microscopy, X-ray powder diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller (BET) and thermogravimetry analysis. The data showed that the nanoparticles have spherical morphology with an average size of about 40 nm and 49.16 m(2)/g BET surface area. The inductively coupled plasma analysis confirmed that the Pd2+ had been successfully loaded on the Fe3O4@SiO2@DPA support with a high amount of 1.03 mmol g(-1). The synthesized nanocatalyst was considered for synthesis of biaryls by the Suzuki-Miyaura coupling reaction in water/ethanol as the solvent system and in the absence of toxic phosphine ligand. The reaction conditions were mild, and coupling reaction yields were excellent (68-95%). The synthesis is compatible with the environment. The nanocatalyst can be easily recycled from the reaction mixture using an external magnet and was used at least five times without significant loss of catalytic activity.