Superoxo, μ-peroxo, and μ-oxo complexes from heme/O2 and heme-Cu/O2 reactivity:: Copper ligand influences in cytochrome c oxidase models

The O-2-reaction chemistry of 1:1 mixtures of (F-8)Fe-11 (1; F-8 = tetrakis(2,6-diflurorophenyl)porphyrinate) and [(L-Me2N)Cu-1](+) (2; L-Me2N = N,N-bis(2-[2-(N',N'-4-dimethylamino)pyridyl]ethyl)methylamine) is described, to model aspects of the chemistry occurring in cytochrome c oxidase. Spectroscopic investigations, along with stopped-flow kinetics, reveal that low-temperature oxygenation of 1/2 leads to rapid formation of a heme-superoxo species (F-8)Fe-111_ (O-2(-)) (3), whether or not 2 is present. Complex 3 subsequently reacts with 2 to form [(F-8)Fe-111_(O-2(2-))-Cu-11(L-Me2N)](+) (4), which thermally converts to [(F-8)Fe (111-)(O)-Cu-11(L-Me2N)](+) (5), which has an unusually bent (Fe-O-Cu) bond moiety. Tridentate chelation, compared with tetradentate, is shown to dramatically lower the nu(O-O) values observed in 4 and give rise to the novel structural features in 5.