Aromatic Methoxylation and Hydroxylation by Organometallic High-Valent Nickel Complexes

Herein we report the synthesis and
reactivity of several organometallic
NiIII complexes stabilized by a modified tetradentate pyridinophane
ligand containing one phenyl group. A room temperature stable dicationic
NiIII–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
NiIII-dihydroxide and NiIII-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 NiIII and NiIV species, in oxidatively
induced C-heteroatom bond formation reactions.