Connecting Organometallic Ni(III) and Ni(IV): Reactions of Carbon-Centered Radicals with High-Valent Organonickel Complexes

This paper describes the one-electron interconversions of isolable Ni-III and Ni-IV complexes through their reactions with carbon-centered radicals (R center dot). First, model Ni-III complexes are shown to react with alkyl and aryl radicals to afford Ni-IV products. Preliminary mechanistic studies implicate a pathway involving direct addition of a carbon-centered radical to the Ni-III center. This is directly analogous to the known reactivity of Ni-II complexes with R center dot, a step that is commonly implicated in catalysis. Second, a Ni-IV-CH3 complex is shown to react with aryl and alkyl radicals to afford C-C bonds via a proposed S(H)2-type mechanism. This pathway is leveraged to enable challenging H3C-CF3 bond formation under mild conditions. Overall, these investigations suggest that Ni-II/III/IV sequences may be viable redox pathways in high-oxidation-state nickel catalysis.