Size-tuned hydrogel network of palladium-confining polymer particles: a highly active and durable catalyst for Suzuki coupling reactions in water at ambient temperature

Poly(N-isopropylacrylamide)-based hydrogel particles (GPs) with different sized hydrogel networks were developed and used to confine a palladium (Pd) catalyst. The size of the gel network was tuned by varying the feed ratio of the cross-linking monomer. Nanosized-Pd(0) was loaded into the GPs, which contain a tertiary-amine ligand, via Pd-ion adsorption and subsequent reduction. The Pd-loaded GPs were used as the catalyst for a Suzuki coupling reaction between phenylboronic acid and 4-bromobenzoic acid in water at 30 °C. Due to the hydrophilic reaction platform provided by the hydrogel matrix of the GPs, the catalytic efficiencies of Pd-loaded GPs were significantly higher than those of commercially available Pd-loaded supports. Notably, the Pd-loaded GPs with the smallest gel networks were highly durable for Suzuki coupling reactions. It is plausible that the smaller network minimized or prevented the enlargement of Pd(0) during the catalytic cycle. The facile synthesis of the GPs, environmentally benign catalytic system, and high catalytic durability and activity of these Pd-loaded GPs are all important factors for the industrial application of these materials.