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

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 super(-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 (PdCl sub(2) 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 degree C.