Ultrafine and Highly Dispersed Pd/SiO2 for Suzuki−Miyaura Cross-coupling Reactions

Abstract

Construction of heterogeneous Pd/SiO2 catalyst via the pollution-free strategy marked strong electrostatic adsorption has been reported for the application to Suzuki–Miyaura cross-coupling reactions. The exposed negatively charged oxygen groups, which were converted from the hydroxyl groups on the surface of silica under the alkaline atmosphere, could effectively anchor palladium species to form ultrafine Pd nanoparticles (Pd NPs) with an average particle size of 1.3 nm and high dispersion (43%). Pd/SiO2 catalyst was endowed with the excellent catalytic performance which was that the yield of the Suzuki–Miyaura reaction between bromobenzene and phenylboronic acid at 40 °C was > 99% for 30 min and the TOF was ~ 80,000 h−1. The catalyst could be easily recovered and recycled by facile procedure without a significant decrease in catalytic activity, which was able to maintain the 90% yield after repeated for 8 times. In addition, a continuous flow reaction device was designed using the Pd/SiO2 catalyst to effectively improve the production efficiency of biphenyl. Pd/SiO2 catalyst constructed with the strategy of strong electrostatic adsorption (SEA) possesses uniformly dispersed and highly exposed Pd sites which can be easily transformed into electron-deficient Pdδ+ and strengthened stability for itself due to its strong interaction with the front surface of the carrier, and has been endowed the outstanding catalytic performance for Suzuki−Miyaura cross-coupling reaction.