Os(II)-catalyzed γ-C(sp3)–H amidation and meta-C(sp2)–H alkylation by fine-tuning the characteristics of in-situ-generated C–Os σ bonds

Transition metal-catalyzed C–H functionalization has recently emerged as a powerful synthetic tool for accessing various value-added structural motifs. However, addressing the remote C–H activation including γ-C(sp3)–H and meta-C(sp2)–H versions is far less investigated and more challenging than that of ortho-C(sp2)–H activation. By fine-tuning the characteristics of the C–osmium (Os) σ bond in situ generated by the phenylpyridine scaffold-mediated ortho-C–H activation/C,N-bidentate coordination, either Os(II)-catalyzed intramolecular γ-C(sp3)–H amidation or intermolecular meta-C(sp2)–H alkylation has been realized in a highly efficient and chemo-/site-/region-selective manner. Through integrated experimental and computational mechanistic studies, the principle of the observed selectivity and two distinct reaction pathways, involving the Os(IV)-nitrenoid-mediated Os(II)-Os(IV)-Os(II) catalytic cycle and the Os(III)-radical-enabled Os(II)-Os(III)-Os(II) SET process, respectively, have been also clarified. Taken together, it provides an insightful reference benchmark for the future development of more wonderful C–H functionalizations mediated by transition metals, especially by less-explored Os.