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(-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 degrees C.