Nickel(IV) Intermediates in Aminoquinoline-Directed C(sp2)–C(sp3) Coupling

We use a ligand design strategy to isolate a cyclometalated nickel(IV) complex that is directly analogous to a key intermediate proposed in aminoquinoline-directed C-H functionalization catalysis. This nickel(IV) complex is formed by oxidative addition of a diaryliodonium reagent to an anionic nickel(II)-picolinate precursor. The nickel(IV) σ-aryl complex is stable at room temperature but undergoes C(sp²)-C(sp³) bond-forming reductive elimination under mild conditions (70 °C, 120 min). Overall, this study demonstrates the accessibility of long-sought-after nickel(IV) intermediates in C-H functionalization catalysis. Furthermore, it demonstrates that LX-type (bidentate, mono-anionic) ligands such as picolinate dramatically stabilize these nickel(IV) species.