Iridium-Catalyzed Regioselective Borylation through C-H Activation and the Origin of Ligand-Dependent Regioselectivity Switching.

Research efforts in catalytic regioselective borylation using C-H bond activation of arenes have gained considerable recent attention. The ligand-enabled regiocontrol, such as in the borylation of benzaldehyde, the selectivity could be switched from the to position, under identical conditions, by just changing the external ligand () from 8-aminoquinoline () to tetramethylphenanthroline (). The DFT(B3LYP-D3) computations helped us learn that the energetically preferred catalytic pathway includes the formation of an Ir-π-complex between the active catalyst [Ir()(Bpin)] and benzaldimine, a C-H bond oxidative addition (OA) to form an Ir(V)aryl-hydride intermediate, and a reductive elimination to furnish the borylated benzaldehyde as the final product. The lowest energetic span (δ = 26 kcal/mol with ) is noted in the borylation pathway, with the OA transition state (TS) as the turnover-determining TS. The change in regiochemical preference to the borylation (δ = 26) with is identified. A hemilabile mode of participation is found to exhibit a δ of 24 kcal/mol for the borylation, relative to that in the chelate mode (δ = 26 kcal/mol). The predicted regioselectivity switching is in good agreement with the earlier experimental observations.