Ruthenaphoto-catalyzed ortho-C−H alkylation with secondary alkyl halides: SET-enabled ruthenium(II/III/IV) manifold

The activation of organic halides by transition metals is one of the most important elementary processes in organic synthesis, which can be achieved by a two-electron oxidation addition process or a one-electron radical process. Currently, the ruthenium-catalyzed meta-C(sp²)–H alkylation with alkyl halides has emerged as a robust tool for remote C(sp²)–H functionalization and was unambiguously proved to occur via a radical pathway. By contrast, the modus operandi of ruthenium-catalyzed ortho-C(sp²)–H alkylation is still somewhat unclear and was proposed to occur through a two-electron manifold of ruthenium(II/IV) regime. In this context, we reported on a photo-induced ruthenium-catalyzed ortho-C(sp²)−H alkylation with secondary/primary alkyl bromides. Mechanistic studies by experiment and computation provide strong support for a ruthenium(II/III/IV) regime, involving a SET between alkyl bromide and the in situ-generated bicycloruthenated complex.