Mechanism and regioselectivity of [Cu-Fe] heterobimetallic-catalyzed hydroboration of pyridines: DFT investigation

Dearomatization of pyridine is important in organic synthesis while the control of its selectivity is difficult, the hydroboration catalyzed by transitional metal is an effective solution. In this work, the detailed reaction mechanism of hydroboration of pyridines catalyzed by [Cu-Fe] heterobimetallic catalyst was investigated by density functional theory (DFT) calculations. The catalytic mechanism and the influence factors of catalytic activity and regioselectivity were discussed. Our calculated results show that the hydroboration of pyridines catalyzed by the [Cu-Fe] heterobimetallic catalyst involves three processes: B-H bond activation, activated Bpinpyridine formation, and Bpin-pyridine reduction addition. The activated Bpin-pyridine formation process is the rate-determining step. In the Bpin-pyridine reduction addition process, the addition reaction proceeds via the ionic intermediate mechanism, instead of the single electron transfer (SET) mechanism. Both the catalytic activity and the regioselectivity are determined by the atomic charge distribution. Our calculation results are consistent with and provide an explanation for the experimental observations, being particularly helpful for the further development of pyridine dearomatization and the design of other catalytic transformations.