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
%.