Iron-Catalyzed Direct Suzuki–Miyaura Reaction: Theoretical and Experimental Studies on the Mechanism and the Regioselectivity

The mechanism of the Suzuki–Miyaura cross-coupling reaction between pyridine and phenylboronic acid catalyzed by the complex of iron salt combined with macrocyclic polyamine (iron–MCPA) was investigated theoretically and experimentally. It was found that the overall reaction includes three steps: C–H activation, transmetalation, and reductive elimination. The results indicate that the rate-determining step is the transmetalation step. The C–H activation of a different position on pyridine is the origin of the regioselectivity. The transmetalation step is the regio-determining step. Both the C–H activation and the transmetalation steps favor the regioselective formation of the ortho product. The oxoiron complex is predicted to be the active species theoretically and is confirmed by experiments. The calculations correctly reproduce the major product, 2-phenylpyridine, which is consistent with the experimental observation.