Imidazole ligation of metals through histidine is extensive among metalloproteins and enzymes, yet the role of the imidazolate conjugate base is often neglected, despite its potential accessibility when bonded to a highly oxidized metal center. Using synthetic models of oxygenated tyrosinase enzymes with exclusive monodentate imidazole ligation, we find that deprotonation of the μ2-η2:η2-peroxidodicopper(II) species triggers redox isomerization to an imidazolate-ligated bis(μ2-oxido)dicopper(III) species. Formal two-electron oxidation to Cu(III) remains unprecedented in biological systems, yet is effected readily by addition of base in these model systems. Spectrophotometric titrations by UV/visible/near-IR and copper K-edge X-ray absorption spectroscopies are interpreted most simply as two cooperative, 2H+ transformations in which the peroxide O-O is cleaved in the first step. Elaboration from simple imidazoles to a protected histidine extends this isomerization into an amino acid environment. The role of phenolate as a base suggests this four-electron reduction of O2 is energetically viable in a biological context and requires only two copper centers, which act as two-electron shuttles when imidazole deprotonation assists. This existential precedent of viable imidazolate intermediates invites speculation into an alternative mechanism for phenol hydroxylation not previously considered at Type 3 copper sites such a tyrosinases.