Polymer microgel-stabilized palladium nanoparticles as efficient catalysts for reduction and Suzuki-Miyaura coupling reactions

Poly( N -isopropylmethacrylamide-co-acrylamide-co-acrylic acid) [p(NPMAA)] microgel particles were synthesized by employing the free radical precipitation polymerization method. Spherical palladium nanoparticles were successfully incorporated into the p(NPMAA) microgel system. The morphology and stability of purified p(NPMAA) microgels and the p(NPMAA) microgels loaded with palladium nanoparticles [Pd-[p(NPMAA)]] were examined by TEM, TGA, FT-IR, and XRD techniques. The catalytic activity of the Pd-[p(NPMAA)] system was evaluated for two different organic transformations (Suzuki-Miyaura coupling and nitroarenes reduction reactions). Under green solvent conditions, a series of nitroarenes were effectively converted to corresponding aryl amines with good to excellent yields (91–96 %). The Pd-[p(NPMAA)] microgel particles rapidly and efficiently catalyzed the Suzuki-Miyaura coupling reaction of different boronic acids with several aryl halides and produced corresponding biaryl compounds. Surprisingly, all coupling reactions were accomplished within 02–16 min and provided fabulous yields ranging from 92–99 %. All synthesized compounds were purified and analyzed by 1 H-NMR and 13 C-NMR. The stability, efficiency, and recycling ability of the Pd-[p(NPMAA)] microgel particles proved to be an effective catalyst for both studied transformations. The Pd-[p(NPMAA)] catalyst is stable below 250 °C and can be stored under normal conditions.