Nickel-catalyzed, silyl-directed, ortho-borylation of arenes via an unusual Ni(II)/Ni(IV) catalytic cycle

Nickel-catalyzed C–H bond functionalization reactions provide an impressive alternative to those with noble metal catalysts due to their unique reactivity and low cost. However, the regioselective C(sp2)–H borylation reaction of arenes accomplished by nickel catalyst remains limited. We herein disclose a silyl-directed ortho C(sp2)–H borylation of substituted arenes with a Ni(cod)2/PMe3/KHMDS catalyst system. Using readily available starting materials, this protocol provides easy access to ortho-borylated benzylic hydrosilanes bearing flexible substitution patterns. These products can serve as versatile building blocks for the synthesis of sila or sila/borine heterocycles under mild conditions. Control experiments and DFT calculations suggest that a catalytic amount of base prompts the formation of Ni(II)-Bpin-ate complex, likely related to the C(sp2)–H bond activation. This borylation reaction might follow an unusual Ni(II)/Ni(IV) catalytic cycle. Nickel-catalyzed C–H bond functionalization reactions provide an impressive alternative to those with noble metal catalysts but the regioselective C(sp2)−H borylation reaction of arenes accomplished by nickel catalyst remains challenging. Here the authors disclose a silyl-directed ortho C(sp2)−H borylation of substituted arenes with a Ni(cod)2/PMe3/KHMDS catalyst system.