Encapsulated Gold Nanoparticles as a Reactive Quasi-Homogeneous Catalyst in Base-Free Aerobic Homocoupling Reactions

Multiple gold nanoparticles (AuNPs) are physically encapsulated within a poly(N-isopropylacrylamide) particle at room temperature by an in situ reduction method using trisodium citrate (Cit) and sodium oxalate (Oxa) to serve as quasi-homogeneous catalysts for carbon-carbon bond-forming reactions under base-free aerobic conditions. The use of Oxa results in a more rapid formation and higher loading of AuNPs within the polymer particles compared to those prepared with conventional Cit. Upon dispersing both composite particles in EtOH-rich aqueous solvents, the polymer matrices maintain a fully swollen structure while still providing great stability to the AuNPs whose surfaces are analyzed to be nearly free from the reducing/stabilizing agents. As a catalyst in homocoupling reactions, the composite particles prepared with Oxa exhibit higher activity, selectivity, and recyclability with a much lower activation energy than those prepared with Cit. The preparation of the composite particles and their catalytic properties are optimized under environmentally-friendly reaction conditions, and the relationship between structural features and catalytic functions are examined to potentially develop robust, versatile, and green catalytic systems.