Palladium-catalysed reactions in water using catalysts covalently tethered on a thermo-responsive polymer†

Bidentate N,N-ligand moieties were covalently tethered on a RAFT agent by Hüisgen cycloaddition, and poly(N-isopropylacrylamide) (PNIPAAm) bearing the ligand moiety was obtained by living-radical polymerization using these RAFT agents. The polymer formed a palladium complex covalently immobilized at the terminus of each polymer chain. Palladium-catalysed Mizoroki–Heck and Suzuki–Miyaura cross coupling reactions proceeded in water with these polymer-immobilized Pd catalysts. The products were obtained in good yields and the aqueous layer containing the polymer catalysts could be reused. Electron microscopic analysis suggested that palladium nanoparticles formed during the reaction were responsible for the catalytic activity. Using an NNC-pincer Pd complex tethered on the polymer, the catalytic reaction was completed with 0.01 mol% of Pd loading. The aqueous solution could be reused 8 times, and a turnover number (TON) of up to 82 800 was achieved.