A Bioinspired Non-heme FeIII−(O22−)−CuII Complex with a St = 1 Ground State

Cytochrome c oxidase (CcO) is a heme−copper oxidase (HCO) that catalyzes the natural reduction of oxygen to water. A pro-found understanding of some of the elementary steps leading to the intricate 4e−/4H+ reduction of O2 is presently lacking. A St = 1 FeIII−(O22−)−CuII (IP) 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 in-volvement of IP in the HCO catalytic cycle is, however, missing. A number of heme-copper peroxido complexes have been pre-pared as synthetic models of IP; but all of them possess the catalytically non-relevant St = 0 ground state resulting from antiferro-magnetic coupling between the S = 1/2 FeIII and CuII centers. In a complete non-heme approach, we now report the spectroscopic characterization and reactivity of the FeIII−(O22−)−CuII intermediates 1 and 2, which differ only by a single −CH3 versus −H sub-stituent on the central amine of the tridentate ligands binding to copper. Complex 1 with an end-on peroxido core, and ferromag-netically (St=1) coupled FeIII and CuII centers performs H-bonding mediated O−O bond cleavage in presence of phenol to generate oxoiron(IV), copper(II) and PhO•. In contrast, the side-on peroxide complex 2, with a St = 0 ground-state is unreactive towards phenol. Thus, the implications for spin topology contributions to O−O bond cleavage, as proposed for the heme FeIII−(O22−)−CuII intermediate in CcO, can be extended to non-heme chemistry.