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In this report, we describe new dioxygen reactivity of reduced heme-copper complexes employing the tethered tetraarylporphyrinate ligands 5 L and 6 L. 1 Notably, peroxo complex [( 6 L)Fe III -(O 2 2-)-Cu II ](BAr F ) (2a), 5 formed from the reaction of [( 6 L)Fe II -Cu I ](BAr F ) (1a) with O 2 (Scheme 1), has physical properties and reactivity which contrast greatly with those of the few other hemecopper peroxo complexes described in the literature. [6][7][8] These studies are part of our general program aimed at elucidating fundamental aspects of O 2 -interactions with heme-copper centers, 4,8-12 how copper influences (P)Fe II /O 2 chemistry, and how hemes influence copper(I)-dioxygen reactivity patterns. Insights obtained may pertain to heme-copper oxidase (e.g., cytochrome c oxidase) 13,14 active-site O 2 -binding and reduction, or other oxidative processes involving dioxygen.Reduced Fe II ‚‚‚Cu I heme-copper compounds [( 6 L)Fe II Cu I ]-(BAr F ) (1a) and [( 5 L)Fe II Cu I ](BAr F ) (1b) (Scheme 1) were

In aerobic organisms, the heme a 3 -Cu B binuclear active center in heme-copper oxidases is responsible for O 2 binding, O-O reductive cleavage, and protonation to give H 2 O. 1 The enzyme couples this 4e -/4H + O 2 reduction to the translocation of protons, creating the membrane potential used to drive ATP synthesis. There is considerable interest in developing structural, spectroscopic, and functional active site models, 2-4 but only a few discrete heterobinuclear Fe II ‚‚‚Cu I species have been well characterized and employed for critical O 2 -reactivity studies. 3,[5][6][7][8] We wish to study systems where the (porphyrinate)Fe II /LCu I / O 2 chemistry (L ) copper ligand) may be controlled (but also systematically varied), in situations where intramolecular reactions are favored. Here, we report such chemistry with heterobinucleating ligands, the constitutional isomers 6 L and 5 L, where a tetradentate TMPA 9 ligating moiety is covalently attached to the periphery of a porphryin, through either the 6-position ( 6 L) or the 5-position ( 5 L) of one pyridine arm (Scheme 1). 6 L and 5 L take advantage by employing a Cu ligand with an established (TMPA)Cu I /O 2 chemistry with known kinetics, thermodynamics, structures, and spectroscopy. 10 In addition to the description of new Fe II (with "empty tether") and Fe II ‚‚‚Cu I complexes with 6 L and 5 L, we report biomimetic reactions where µ-oxo Fe III -OCu II cores are generated directly from O 2 reduction; 11 a crystal structure of the 6 L oxygenation product is described.The complexes described herein (Scheme 1) are characterized by multinuclear NMR 12 and UV-visible spectroscopies, and supported by MALDI-TOF mass spectrometry on isolated solids. 13 Metalation begins with addition of excess FeCl 2 to either the 6 L or 5 L ligands, followed by air oxidation. This procedure yields † The Johns Hopkins University. Shinzawa-Itoh, K.; Nakashima, R.; Yaono, R.; Yamashita, E.; Inoue, N.; Yao, M.; Jei-Fei, M.; Libeu, C. P.; Mizushima, T.; Yamaguchi, H.; Tomizaki, T.; Tsukihara, T. Collman, J. P.; Rapta, M.; Bröring, M.; Raptova, L.; Schwenninger, R.; Boitrel, B.; Fu, L.; L'Her, M. J. Am. Chem. Soc. 1999, 121, 1387-1388 and references cited therein. (7) Monzani, E.; Casella, L.; Gullotti, M.; Panigada, N.; Franceschi, F.; Papaefthymiou, V. (a) With separate mononuclear reduced heme and copper(I) complexes, we have previously 11b,c described details of the reaction of (F8-TPP)Fe II plus [(TMPA)Cu I (RCN)] + with O2, which produces the µ-oxo complex [(F8-TPP)Fe III -O-Cu II (TMPA)] + (5). Isotope labeling showed that the oxo atom in 5 is derived from O2, and the reaction stoichiometry (unpublished results) is Fe:Cu:O2 ) 2:2:1. (b) Karlin, K. D.; Nanthakumar, A.; Fox, S.; Murthy, N. N.; Ravi, N.; Huynh, B. H.; Orosz, R. D.; Day, E. P. H NMR spectra, particularly pyrrole resonances, are useful as a criterion for compound purity, since most of the compounds (including impurities) possess paramagnetically shifted and distinctive (i.e., highly sensitive to spin and oxidation ...