Cyclometalated 2-Phenylimidazole Palladium Carbene Complexes in the Catalytic Suzuki–Miyaura Cross-Coupling Reaction

We present the syntheses of 12 cyclometalated palladium C ∧ N 2-phenylimidazole carbene complexes with different N -1 groups as well as different substituents at the C-2 phenyl group of the cyclometalating imidazole. We investigated the influence of these substituents by comparing the catalytic performance of the complexes in the Suzuki–Miyaura cross-coupling reaction of aryl chlorides. We can show a strong dependence between the steric demand of the N -1 substituent of the cyclometalating imidazole and the catalytic activity in the cross-coupling reaction. The most active complex shows a wide substrate scope, where several aryl as well as benzyl chlorides could be coupled with different boronic acids in excellent yields using very low catalyst concentrations of 0.05 mol %.