867368-28-3Relevant articles and documents
Further insights into the spectroscopic properties, electronic structure, and kinetics of formation of the heme-peroxo-copper complex [(F 8TPP)FeIII-(O22-)-Cu II(TMPA)]+
Ghiladi, Reza A.,Chufan, Eduardo E.,Del Rio, Diego,Solomon, Edward I.,Krebs, Carsten,Boi, Hanh Huynh,Huang, Hong-Wei,Moenne-Loccoz, Pierre,Kaderli, Susan,Honecker, Marcus,Zuberbuehler, Andreas D.,Marzilli, Lisa,Cotter, Robert J.,Karlin, Kenneth D.
, p. 3889 - 3902 (2007)
In the further development and understanding of heme-copper O 2-reduction chemistry inspired by the active-site chemistry in cytochrome c oxidase, we describe a dioxygen adduct, [(F8TPP)Fe III-(O22-)-CuII(TMPA)](ClO 4) (3), formed by addition of O2 to a 1:1 mixture of the porphyrinate-iron(II) complex (F8TPP)FeII (1a) {F 8TPP = 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 remarkably stable {t1/2 (RT; MeCN) ≈ 20 min; λmax = 412 (Soret), 558 nm; EPR silent}, and is formulated as a peroxo complex 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; Δ 16O2/18O2 = 46 cm-1; Δ16O2/16/18O2 = 23 cm -1}. Consistent with a μ-η2:η1 bridging peroxide ligand, two metal-O stretching frequencies are 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 characterized μ-oxo complex [(F8TPP)Fe III-O-CuII(TMPA)]+ (4) (known S = 2 system, antiferromagnetically coupled high-spin FeIII and CuII). Moessbauer 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 Moessbauer spectroscopic studies reveal the formation of heme-only superoxide complex (S)(F8TPP)FeIII-(O2 -) (2a) (S = solvent molecule) prior to 3. Thermal decomposition of μ-peroxo complex 3 yields μ-oxo complex 4 with concomitant release of ～0.5 mol O2 per mol 3. Characterization of the reaction 1a/1b + O2 → 2 → 3 → 4, presented here, advances our understanding and provides new insights to heme/Cu dioxygen-binding and reduction.
(F8TPP)FeII/O2 reactivity studies {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate(2-)}: Spectroscopic (UV-visible and NMR) and kinetic study of solvent-dependent (Fe/O2 = 1:1 or 2:1) reversible O2-reduction and ferryl formation
Ghiladi,Kretzer,Guzei,Rheingold,Neuhold,Hatwell,Zuberbuehler,Karlin
, p. 5754 - 5767 (2008/10/08)
In this report, we describe in detail the O2-binding chemistry of the metalloporphyrin (F8TPP)FeII (1). This complex was synthesized from aqueous dithionite reduction of (F8TPP)FeIII-Cl (X-ray structure reported: C55H36ClF8-FeN4O; a = 13.6517(2) A, b = 13.6475(2) A, c = 26.3896(4), α = 90°, β = 89.9776(4)°, γ = 90°; monoclinic, P2(1)/c, Z = 4). Complex 1 crystallizes from toluene/heptane solvent system as a bis(toluene) solvate, (F8TPP)FeII·(C7H8) 2, with ferrous ion in the porphyrin plane (C58H36F8FeN4; a = 20.9177(2) A, b = 11.7738(2) A, c = 19.3875(2), α = 90°, β = 108.6999(6)°, γ = 90°; monoclinic, C2/c, Z = 4; Fe-N4(av) = 2.002 A, N-Fe-N (all) = 90.0°). Close metal-arene contacts are also observed at 3.11-3.15 A. Upon oxygenation of 1 at 193 K in coordinating solvents, UV-visible and 2H and 19F NMR spectroscopies revealed the presence of a reversibly formed dioxygen adduct, formulated as the heme-superoxo complex (S)(F8TPP)FeIII-(O2-) (2) (S = solvent) [(i) tetrahydrofuran (THF) solvent: UV-visible, 416 (Soret), 536 nm; 2H NMR: δpyrrole 8.9 ppm; (ii) EtCN solvent: UV-visible, 414 (Soret), 536 nm; (iii) acetone solvent: UV-visible, 416 (Soret), 537 nm; 2H NMR: δpyrrole 8.9 ppm]. Dioxygen-uptake manometry (THF, 193 K) revealed an O2:1 oxygenation stoichiometry of 1.02:1, consistent with the heme-superoxo formulation of 2. Stopped-flow UV-visible spectrophotometry studies of the (F8TPP)FeII (1)/O2 reaction in EtCN and THF solvents were able to provide kinetic and thermodynamic insight into the reversible formation of 2 [(i) EtCN: ΔH° = -40 ± 5 kJ/mol; ΔS° = -105 ± 23 J/(K mol); k1 = (5.57 ± 0.04) × 103 M-1 s-1 (183 K); ΔH? = 38.6 ± 0.2 Jd/mol; ΔS? = 42 ± 1 J/(K mol); (ii) THF: ΔH° = -37.5 ± 0.4 kJ/mol; ΔS° = -109 ± 2 J/(K mol)}. The (F8TPP)FeII (1)/O2 reaction was also examined at reduced temperatures in noncoordinating solvents (toluene, CH2Cl2), where UV-visible and 2H and 19F NMR spectroscopies also revealed the presence of a reversibly formed adduct, formulated as the peroxo-bridged dinuclear complex [(F8TPP)FeIII]2-(O22-) (3) [CH2Cl2: UV-visible, 414 (Soret), 535 nm; 2H NMR, δpyrrole 17.5 ppm]. Dioxygen-uptake spectrophotometric titrations revealed a stoichiometry of 2 (F8TPP)FeII (1) per O2 upon full formation of 3. Addition of a nitrogenous base, 4-(dimethylamino)pyridine, to a cold solution of 3 in dichloromethane gave rapid formation of the iron(IV)-oxo ferryl species (DMAP)(F8TPP)FeIV=O (4), based upon UV-visible [417 (Soret), 541 nm] and 2H NMR (δpyrrole = 3.5 ppm) spectroscopic characterization. These detailed investigations into the O2-adducts and ferryl species formed from (F8TPP)FeII (1) may be potentially important for a full understanding of our ongoing heme-copper oxidase model studies, which employ 1 or similar tethered (i.e., covalently attached Cu-chelate) porphyrin analogues in heme/Cu heterobinuclear systems.
