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 beta-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.