Cytochrome c oxidase (CcO) is a heme copper oxidase (HCO) that catalyzes the natural reduction of oxygen to water. A profound understanding of some of the elementary steps leading to the intricate 4e(-)/4H(+) reduction of O-2 is presently lacking. A total spin S-t = 1 Fe-III-(O-2(2-))-Cu-II (I-P) intermediate is proposed to reduce the overpotentials associated with the reductive O-O bond rupture by allowing electron transfer from a tyrosine moiety without the necessity of any spin-surface crossing. Direct evidence of the involvement of I-P in the CcO catalytic cycle is, however, missing. A number of heme copper peroxido complexes have been prepared as synthetic models of I-P, but all of them possess the catalytically nonrelevant S-t = 0 ground state resulting from antiferromagnetic coupling between the S = 1/2 Fe-III and Cu-II centers. In a complete nonheme approach, we now report the spectroscopic characterization and reactivity of the Fe-III-(O-2(2-))-Cu-II intermediates 1 and 2, which differ only by a single -CH3 versus -H substituent on the central amine of the tridentate ligands binding to copper. Complex 1 with an end-on peroxido core and ferromagnetically (S-t = 1) coupled Fe-III and Cu-II centers performs H-bonding-mediated O-O bond cleavage in the presence of phenol to generate oxoiron(IV) and exchange-coupled copper(II) and PhO center dot moieties. In contrast, the mu-eta(2):eta(1) peroxido complex 2, with a S-t = 0 ground state, is unreactive toward phenol. Thus, the implications for spin topology contributions to O-O bond cleavage, as proposed for the heme Fe-III-(O-2(2-))-Cu-II intermediate in CcO, can be extended to nonheme chemistry.