The iron−copper dinuclear active site in heme-copper oxidases (e.g., cyctochrome c oxidase) has spurred the development of the inorganic chemistry of bridged heme-copper complexes, including species possessing (porphyrinate)FeIII−O(H)−CuII−L moieties. We describe here the synthesis, by two routes, of [(F8TPP)FeIII−O−CuII(MePY2)]+ (5) {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate; MePY2 = N,N-bis[2-(2-pyridyl)ethyl]methylamine}. First, 5-(CF 3 SO 3 ) was generated by reaction of [(MePY2)CuII](CF3SO3)2 (3-(CF 3 SO 3 ) 2 ) and [(F8TPP)FeIII−OH] (4) with triethylamine in THF or CH3CN in 65−70% yield. The complex was also prepared by reduction of O2 by a 1:1 mixture of copper(I) and iron(II) complexes, [(MePY2)CuI(CH3CN)](BArF) (1-(BArF)) (BArF = tetrakis(3,5-bis-trifluoromethylphenyl)borate) and (F8TPP)FeII (2) in O2-saturated THF or acetone, at −80 °C with subsequent warming to room temperature. Preliminary stopped-flow kinetics on the O2 reaction with the 1:1 mixture show the formation of at least two intermediates (i.e., a superoxo species (F8TPP)Fe−O2 first, and then a presumed peroxo-bridged Fe−O2−Cu species) prior to the formation of the final μ-oxo complex [(F8TPP)FeIII−O−CuII(MePY2)]+ (5-(BArF)). The 1H NMR spectrum of 5-(CF 3 SO 3 ) in CD2Cl2 exhibits a pyrrole peak at 67.7 ppm (corroborated by 2H NMR), while downfield (23.4 and 18.9 ppm) and dramatically upfield-shifted resonances (−87.7, −155.4 and −189.4) have been assigned to hydrogens of the MePY2 moiety, by specific deuteration. The μ-hydroxo complex [(F8TPP)Fe−(OH)−Cu(MePY2)](OTf)2 (6-(CF 3 SO 3 ) 2 ) was synthesized by addition of 3-(CF 3 SO 3 ) 2 to 4 in CH3CN, or by protonation of 5-(CF 3 SO 3 ) with CF3SO3H. In a 1H NMR-spectroscopic protonation titration (CF3SO3H), the pyrrole 67.7 ppm resonance for 5-(CF 3 SO 3 ) progressively converts to 70.3 ppm, diagnostic of 6-(CF 3 SO 3 ) 2 . The protonation is slow on the NMR time scale. The 1H NMR spectral properties are consistent with antiferromagnetically coupled high-spin iron(III) and Cu(II) ions (S = 2 spin state), and the interaction is weaker in 6-(CF 3 SO 3 ) 2 (5-(CF 3 SO 3 ), μeff = 5.05 μB; 6-(CF 3 SO 3 ) 2, μeff = 5.60 μB; Evans NMR method). By titration using a series of organic acids, the pK a for 6-(CF 3 SO 3 ) 2 has been estimated to be 16.7 < pK a < 17.6 (CH3CN solvent), or 9.6 ± 2 (aqueous). Plots of δ vs 1/T for both μ-oxo and μ-hydroxo complexes 5-(CF 3 SO 3 ) and 6-(CF 3 SO 3 ) 2 have been obtained, showing linear Curie (for downfield resonances) or anti-Curie (for upfield peaks) behavior.

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Our continuing interest in developing reactivity models for the heme a 3 -Cu B O 2 -binding, O 2 -reduction, and proton pumping site in heme-copper oxidases 1,2 (e.g., cytochrome c oxidase (CcO)) 2-5 includes investigation of reactions of dioxygen with (porphyrinate)Fe II and (L Cu )Cu I complexes. [6][7][8][9] Thus, (F 8 TPP)Fe II /[(L Cu )-Cu I ] + /O 2 reactions lead to O-O reductive cleavage and generation of µ-oxo complexes [(F 8 TPP)Fe III -O-Cu II (L Cu )] + , 10 when employing pyridyl-alkylamine copper-ligand donors, either an N 4 tetradentate L Cu ) TMPA or tridentate chelate L Cu ) R-PY2. 9,10 A developing approach in our laboratories 6,14-16 and others [17][18][19][20][21] is to utilize heterobinucleating ligands for such heme/Cu/O 2 -reactivity studies. We recently showed that reduced compounds [( n L)Fe II ...Cu I ] + , where n L possess a TMPA moiety covalently tethered to a tetraarylporphyrin periphery, react with O 2 giving analogous µ-oxo complexes [( n L)Fe III -O-Cu II ] + . 13,16 Here, we describe oxygenation chemistry using 3 L and 4 L (Scheme 1), with new features: (1) a PY2 10 tridentate chelate is built in, to match the number and type of N-ligands observed in CcO. [3][4][5] (2) while the copper ligands possess the PY2 unit, taking advantage of previously established Cu I /O 2 chemistry, [22][23][24] (3) a heme axial pyridyl ligand is tethered to the porphryin periphery distal to the PY2 Cu ligand, mimicking the CcO arrangement, 3-5 and (4) 3 L and 4 L possess different linkers to the PY2 and pyridine base; such model compound variations provide a way to probe the effects of subtle changes in metal environment, analogous to protein enforced active-site geometric relationships. 25 Syntheses of 3 L and 4 L, 26 metalation (FeCl 2 ), air oxidation, and column chromatography yield porphyrinate-iron(III) complexes with an empty PY2 tether, ( 3/4 L)Fe III -OH (λ max ) 413-415 nm; δ pyrrole ) ∼80 ppm (room temperature)), 26 with spectrosopic properties paralleling those of (F 8 TPP)Fe III -OH. 12 (1) García-Horsman, J. A.; Barquera, B.; Rumbley, J.; Ma, J.; Gennis, R. B. 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. Science 1998, 280, 1723-1729. (5) Ostermeier, C.; Harrenga, A.; Ermler, U.; Michel, H. Abbreviations used: F8TPP, tetrakis(2,6-difluorophenyl)porphyrinate; TMPA, tris(2-pyridylmethyl)amine; R-PY2, N,N-bis[2-(2-pyridyl)ethyl]-R-amine; BArF ) B[3,5-(CF3)2C6H3]4 -. (11) These same µ-oxo complexes can also be synthesized from acid-base self-assembly procedures. 9,12,13 (12) Fox, S.; Nanthakumar, A.; Wikström, M.; Karlin, K. D.; Blackburn, N. J. J. Am. Chem. Soc. 1996, 118, 24-34. (13) Obias, H. V.; van Strijdonck, G. P. F.; Lee, D.-H.; Ralle, M.; Blackburn, N. J.; Karlin, K. D. J. Am. Chem. Soc. 1998, 120, 9696-9697. (14) Karlin, K. D.; Fox, S.; Nanthakumar, A.; Murthy, N. N.; Wei, N.; Obias, H. V.; Martens, C. F. Pure Appl. Chem. 1995, 67, 289-296. (15) Martens, C. F.; ...

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