Aromatic Methoxylation and Hydroxylation by Organometallic High-Valent Nickel Complexes

Herein we report the synthesis and reactivity of several organometallic Ni^III complexes stabilized by a modified tetradentate pyridinophane ligand containing one phenyl group. A room temperature stable dicationic Ni^III-disolvento complex was also isolated, and the presence of two available cis coordination sites in this complex offers an opportunity to probe the C-heteroatom bond formation reactivity of high-valent Ni centers. Interestingly, the Ni^III-dihydroxide and Ni^III-dimethoxide species can be synthesized, and they undergo aryl methoxylation and hydroxylation that is favored by addition of oxidant, which also limits the β-hydride elimination side reaction. Overall, these results provide strong evidence for the involvement of high-valent organometallic Ni species, possibly both Ni^III and Ni^IV species, in oxidatively induced C-heteroatom bond formation reactions.