| Abstract
| - In the further development and understanding of heme−copper O2-reduction chemistry inspired by the active-sitechemistry in cytochrome c oxidase, we describe a dioxygen adduct, [(F8TPP)FeIII−(O22-)−CuII(TMPA)](ClO4) (3),formed by addition of O2 to a 1:1 mixture of the porphyrinate−iron(II) complex (F8TPP)FeII (1a) {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate dianion} and the copper(I) complex [(TMPA)CuI(MeCN)](ClO4) (1b) {TMPA = tris(2-pyridylmethyl)amine}. Complex 3 forms in preference to heme-only or copper-only binuclear products, is remarkablystable {t1/2 (RT; MeCN) ≈ 20 min; λmax = 412 (Soret), 558 nm; EPR silent}, and is formulated as a peroxocomplex on the basis of manometry {1a/1b/O2 = 1:1:1}, MALDI-TOF mass spectrometry {16O2, m/z 1239 [(3 +MeCN)+]; 18O2, m/z 1243}, and resonance Raman spectroscopy {ν(O-O) = 808 cm-1; Δ16O2/18O2 = 46 cm-1;Δ16O2/16/18O2 = 23 cm-1}. Consistent with a μ-η2:η1 bridging peroxide ligand, two metal−O stretching frequenciesare observed {ν(Fe-O) = 533 cm-1, ν(Fe-O-Cu) = 511 cm-1}, and supporting normal coordinate analysis is presented.2H and 19F NMR spectroscopies reveal that 3 is high-spin {also μB = 5.1 ± 0.2, Evans method} with downfield-shifted pyrrole and upfield-shifted TMPA resonances, similar to the pattern observed for the structurally characterizedμ-oxo complex [(F8TPP)FeIII−O−CuII(TMPA)]+ (4) (known S = 2 system, antiferromagnetically coupled high-spinFeIII and CuII). Mössbauer spectroscopy exhibits a sharp quadrupole doublet (zero field; δ = 0.57 mm/s, |ΔEQ| =1.14 mm/s) for 3, with isomer shift and magnetic field dependence data indicative of a peroxide ligand and S =2 formulation. Both UV−visible-monitored stopped-flow kinetics and Mössbauer spectroscopic studies reveal theformation of heme-only superoxide complex (S)(F8TPP)FeIII−(O2-) (2a) (S = solvent molecule) prior to 3. Thermaldecomposition of μ-peroxo complex 3 yields μ-oxo complex 4 with concomitant release of ∼0.5 mol O2 per mol3. Characterization of the reaction 1a/1b + O2 → 2 → 3 → 4, presented here, advances our understanding andprovides new insights to heme/Cu dioxygen-binding and reduction.
- Addition of dioxygen to a 1:1 mixture of (F8TPP)FeII (1a) and [(TMPA)CuI(MeCN)]+ (1b) leads to O2-adducts including the heme−superoxo species (solvent)(F8TPP)FeIII−(O2-); attack of this by 1b yields heterobinuclear peroxo complex [(F8TPP)FeIII−(η2:η1-O22-)−CuII(TMPA)]+ (3). New electronic structural insights from Mössbauer and resonance Raman (three distinct Fe−O2−Cu vibrations) spectroscopies support the μ-η2:η1 structure and description of 3 as an overall S = 2 spin system with high-spin ferric heme antiferromagnetically coupled to the copper(II) ion.
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