Controlling the formation of encapsulated gold nanoparticles for highly reactive catalysts in the homocoupling of phenylboronic acid

The reduction of gold ions using four different types of mild reducing agents was carried out in the presence of poly(n-isopropylacrylamide), PNIPAM, particles under light irradiation at room temperature. Simply controlling the concentration ratios of the gold ions to reductants allowed for the systematic formation of physically encapsulated gold nanoparticles (AuNPs) within the PNIPAM particles due to the presence of weak interactions between the guest AuNPs and host PNIPAM particles. After the examination of the structural and physical properties of the AuNPs and their loading efficiency, the composite particles were extensively utilized in the aerobic homocoupling of phenylboronic acid in EtOH to examine their catalytic properties associated with the rate of reaction, selectivity, and activation energy (Ea). All composite particles showed the highly selective formation of the biphenyl product and comparable Ea values, regardless of the size and distribution of the encapsulated AuNPs as catalysts. However, the way the AuNPs were formed within the PNIPAM particles notably influenced the rate of reaction. As such, developing a simple approach to optimize the encapsulation degree of AuNPs and their structural features in the presence of polymer particles can be applied to designing diverse metal-polymer composite particles for rapid and effective catalytic systems.