Palladium immobilized on functionalized hypercrosslinked polymers: a highly active and recyclable catalyst for Suzuki–Miyaura coupling reactions in water

Abstract

Heterogeneous catalysts have shown advantages such as high stability, good recyclability and easy separation from reactants over homogeneous catalysts in recent years. In this paper, three pyridine-functionalized N-heterocyclic carbene–palladium complexes (HCP-Pd) were successfully synthesized via a simple external cross-linking reaction. In each catalyst (i.e., complex), palladium (Pd) was immobilized on the hypercrosslinked polymer (HCP) via formation of a six-membered ring by Pd²⁺ and the bidentate ligands of NHC and pyridine. The structure and composition of HCP-Pd were characterized by SEM, TEM, N₂ sorption, FT-IR, TGA and XPS. The catalytic performances of these catalysts in a Suzuki–Miyaura coupling reaction were also studied. The results prove that HCP-Pd is a very effective heterogeneous catalyst for the Suzuki–Miyaura coupling reaction of various aryl halides with aryl boronic acid in an aqueous medium under mild conditions.