Agglomeration of Pd0 nanoparticles causing different catalytic activities of Suzuki carbonylative cross-coupling reactions catalyzed by PdII and Pd0 immobilized on dopamine-functionalized magnetite nanoparticles

Abstract

Solvent-dispersible magnetite nanoparticles (Fe₃O₄) end-functionalized with amino groups were successfully prepared by a facile one-pot template-free method to immobilize Pd^II and Pd⁰ using a metal adsorption and reduction procedure. They were characterized by TEM, XRD, XPS, FT-IR and VSM. Interestingly, the Pd^II catalyst exhibited better catalytic activity for carbonylative cross-coupling reactions than the Pd⁰ catalyst. According to the catalytic activities of a variety of arylboronic acids and aryl iodides catalyzed by two kinds of Pd catalysts, the proposed reaction mechanism of Suzuki carbonylative cross-coupling reactions using the Pd catalyst was also inferred. More importantly, agglomeration of Pd⁰ nanoparticles was obviously observed in the TEM images of the catalysts after reactions. Therefore, agglomeration of Pd⁰ nanoparticles should be considered as a significant reason for different catalytic activities of the reactions catalyzed by immobilized Pd^II and Pd⁰ catalysts. Furthermore, the Pd^II catalyst revealed high efficiency and stability during recycling stages.