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

Abstract

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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document} ) (3), whether or not 2 is present. Complex 3 subsequently reacts with 2 to form [(F 8 )Fe III –(O \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{2-}}}\end{equation*}\end{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.