A Bioinspired Nonheme Fe III -(O 2 2- )-Cu II Complex with an S t = 1 Ground State.

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 -CH 3 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 • moieties. In contrast, the μ-η 2 :η 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.