Mechanism determination on [LCu-Fp] heterobimetallic-catalyzed C-H borylation of benzene and regioselectivity regulation: A DFT investigation

Abstract

The heterobimetallic complex [(NHC)Cu-FeCp(CO)2] ([LCu-Fp]) is an efficient and sustainable catalyst for C-H borylation under UV light irradiation, whereas the catalytic mechanism is still debating. One opinion is the thermal induced mechanism, in which Cu-Fe bond in [LCu-Fp] firstly dissociated by B-H activation, and then induced the decarbonylation of FpBpin by UV irradiation. The other is the UV-induced mechanism, the decarbonylation of [LCu-Fp] occurred before the Cu-Fe broken. In this work, detailed mechanism of UV-induced has been investigated by DFT calculations and compared with the thermal induced mechanism. Our calculated results show that both of them can occur under UV light irradiation at room temperature. The UV-induced mechanism contains four steps: CO dissociation, Cu-Fe bond breakage by B-H activation, C-H borylation, and H-H reductive elimination. In the last step, it is the re-coordination of CO to the Fe occurs before the releasing of H2. The strong election-withdrawing substituent of benzene would increase the yield of para-product, whereas the election-donating substituent has little influence on the regioselectivity. Our calculation determines the detail mechanism of the title reaction and provides reasonable explanation for the regioselectivity of C-H borylation of substituted benzene, which would help for the widely usages of the heterobimetallic catalysts.