Mechanistic investigation of Ir-catalyzed CH borylation of methyl benzoate: ligand eects in regioselectivity and activity

The Ir-catalyzed C–H borylation of methyl benzoate has been studied with DFT methodology in order to understand the experimentally observed ligand-induced regioselectivity and activity when different [(ligand)Ir(Bpin)₃] catalysts are employed. While bidentate ligands such as 4,4′-di-^tBu-2,2′-bipyridine (dtbpy) completely inhibit ortho-borylation, the use of selected triphenylphosphine derivatives enables the reaction on that position, avoiding the meta– and para-regioisomers. The analysis of the catalytic cycles for the borylation reactions with dtbpy, PPh₃, P(p-CF₃C₆H₄)₃, and P(m,m-(CF₃)₂C₆H₃)₃ allows the interpretation of the observed ligand effects. The different reactivity observed for the different monodentate phosphine ligands can also be rationalized in terms of catalyst stability.