Superoxo, μ-peroxo, and μ-oxo complexes from heme/O 2 and heme-Cu/O 2 reactivity: Copper ligand influences in cytochrome c oxidase models

The O 2 -reaction chemistry of 1:1 mixtures of (F 8 )Fe II (1; F 8 = tetrakis(2,6-diflurorophenyl)porphyrinate) and [(L Me 2 N )Cu I ] + (2; L Me 2 N = 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 III -(O [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₂⁻}}{equation*}{document} ) (3), whether or not 2 is present. Complex 3 subsequently reacts with 2 to form [(F 8 )Fe III –(O [12pt]{minimal} {amsmath} {wasysym} {amsfonts} {amssymb} {amsbsy} {mathrsfs} {}{-69pt} {document} {equation*}{{₂²⁻}}{equation*}{document} )–Cu II (L Me 2 N )] + (4), which thermally converts to [(F 8 )Fe III –(O)–Cu II (L Me 2 N )] + (5), which has an unusually bent (Fe–O–Cu) bond moiety. Tridentate chelation, compared with tetradentate, is shown to dramatically lower the ν(O–O) values observed in 4 and give rise to the novel structural features in 5.