A magnetically separable palladium catalyst containing a bulky N-heterocyclic carbene ligand for the Suzuki–Miyaura reaction

Abstract

This work describes the preparation and characterization of a magnetic palladium catalyst with bulky N-heterocyclic carbene (NHC) ligands for the Suzuki–Miyaura cross-coupling reaction. After the 1-(2,6-diisopropylphenyl)-1H-imidazole (1-arylimidazole) was modified on the surface of magnetic polymer carriers, palladium diacetate was employed to synthesize the Pd-NHC complex, affording a palladium loading of 0.23 mmol g⁻¹. This magnetic catalyst showed high catalytic activity towards the Suzuki–Miyaura reaction of phenylboronic acids with aryl bromides in the ethanol–water solution (TON > 87 000). After 21 cycling runs, its catalytic activity decreased slightly, and no leaking of palladium was found either in products or in reaction residue. When other sources of palladium (PdCl₂ and 3-Cl-pyridinyl) were employed to synthesize the palladium complex, the stability of the magnetic catalyst was greatly improved to perform the catalysis of Suzuki–Miyaura reactions with aryl chlorides at 100 °C.