Nickel Catalysis via S2 Homolytic Substitution: The Double Decarboxylative Cross-Coupling of Aliphatic Acids.

Cross-coupling platforms are traditionally built around a sequence of closed-shell steps, such as oxidative addition, transmetalation, and reductive elimination. Herein, we describe a dual photo/nickel catalytic manifold that performs cross-coupling via a complementary sequence involving free radical generation, radical sorting via selective binding to a Ni(II) center, and bimolecular homolytic substitution (S2) at a high-valent nickel-alkyl complex. This catalytic manifold enables the hitherto elusive cross-coupling of diverse aliphatic carboxylic acids to generate valuable C(sp)-C(sp)-products. Notably, the powerful S2 mechanism provides general access to sterically encumbered quaternary carbon centers, addressing a long-standing challenge in fragment coupling chemistry.