70936-35-5Relevant academic research and scientific papers
Mechanism of Catalytic O2 Reduction by Iron Tetraphenylporphyrin
Pegis, Michael L.,Martin, Daniel J.,Wise, Catherine F.,Brezny, Anna C.,Johnson, Samantha I.,Johnson, Lewis E.,Kumar, Neeraj,Raugei, Simone,Mayer, James M.
supporting information, p. 8315 - 8326 (2019/06/04)
The catalytic reduction of O2 to H2O is important for energy transduction in both synthetic and natural systems. Herein, we report a kinetic and thermochemical study of the oxygen reduction reaction (ORR) catalyzed by iron tetraphenylporphyrin (Fe(TPP)) in N,N′-dimethylformamide using decamethylferrocene as a soluble reductant and para-toluenesulfonic acid (pTsOH) as the proton source. This work identifies and characterizes catalytic intermediates and their thermochemistry, providing a detailed mechanistic understanding of the system. Specifically, reduction of the ferric porphyrin, [FeIII(TPP)]+ , forms the ferrous porphyrin, FeII(TPP), which binds O2 reversibly to form the ferricsuperoxide porphyrin complex, FeIII(TPP)(O2 ?-). The temperature dependence of both the electron transfer and O2 binding equilibrium constants has been determined. Kinetic studies over a range of concentrations and temperatures show that the catalyst resting state changes during the course of each catalytic run, necessitating the use of global kinetic modeling to extract rate constants and kinetic barriers. The rate-determining step in oxygen reduction is the protonation of FeIII(TPP)(O2 ?-) by pTsOH, which proceeds with a substantial kinetic barrier. Computational studies indicate that this barrier for proton transfer arises from an unfavorable preassociation of the proton donor with the superoxide adduct and a transition state that requires significant desolvation of the proton donor. Together, these results are the first example of oxygen reduction by iron tetraphenylporphyrin where the pre-equilibria among ferric, ferrous, and ferric-superoxide intermediates have been quantified under catalytic conditions. This work gives a generalizable model for the mechanism of iron porphyrin-catalyzed ORR and provides an unusually complete mechanistic study of an ORR reaction. More broadly, this study also highlights the kinetic challenges for proton transfer to catalytic intermediates in organic media.
Six-coordinate ferric porphyrins containing bidentate N-t-butyl-N-nitrosohydroxylaminato ligands: Structure, magnetism, IR spectroelectrochemisty, and reactivity
Xu, Nan,Christian, Jonathan H.,Dalal, Naresh S.,Abucayon, Erwin G.,Lingafelt, Colin,Powell, Douglas R.,Richter-Addo, George B.
, p. 20121 - 20130 (2015/12/01)
NONOates (diazeniumdiolates) containing the [X{N2O2}]- functional group are frequently employed as nitric oxide (NO) donors in biology, and some NONOates have been shown to bind to metalloenzymes. We report the preparation, crystal structures, detailed magnetic behavior, redox properties, and reactivities of the first isolable alkyl C-NONOate complexes of heme models, namely (OEP)Fe(η2-ON(t-Bu)NO) (1) and (TPP)Fe(η2-ON(t-Bu)NO) (2) (OEP = octaethylporphyrinato dianion, TPP = tetraphenylporphyrinato dianion). The compounds display the unusual NONOate O,O-bidentate binding mode for porphyrins, resulting in significant apical Fe displacements (+0.60 ? for 1, and +0.69 ? for 2) towards the axial ligands. Magnetic susceptibility and magnetization measurements made from 1.8-300 K at magnetic fields from 0.02 to 5 T, yielded magnetic moments of 5.976 and 5.974 Bohr magnetons for 1 and 2, respectively, clearly identifying them as high-spin (S = 5/2) ferric compounds. Variable-frequency (9.4 GHz and 34.5 GHz) EPR measurements, coupled with computer simulations, confirmed the magnetization results and yielded more precise values for the spin Hamiltonian parameters: gavg = 2.00 ± 0.03, D = 3.89 ± 0.09 cm-1, and E/D = 0.07 ± 0.01 for both compounds, where D and E are the axial and rhombic zero-field splittings. IR spectroelectrochemistry studies reveal that the first oxidations of these compounds occur at the porphyrin macrocycles and not at the Fe-NONOate moieties. Reactions of 1 and 2 with a histidine mimic (1-methylimidazole) generate RNO and NO, both of which may bind to the metal center if sterics allow, as shown by a comparative study with the Cupferron complex (T(p-OMe)PP)Fe(η2-ON(Ph)NO). Protonation of 1 and 2 yields N2O as a gaseous product, presumably from the initial generation of HNO that dimerizes to the observed N2O product.
Selective oxidation of terminal aryl and aliphatic alkenes to aldehydes catalyzed by iron(iii) porphyrins with triflate as a counter anion
Chen, Guo-Qiang,Xu, Zhen-Jiang,Zhou, Cong-Ying,Che, Chi-Ming
, p. 10963 - 10965 (2011/11/06)
[Fe(Por)CF3SO3] (Por = porphyrin dianion) can efficiently catalyze selective oxidation of terminal aryl alkenes and aliphatic alkenes to aldehydes in good to high yields under mild conditions.
Spin-state isomerism in crystalline [FeIII(TPP)(OSO2CF3)]
González, Jorge A.,Wilson, Lon J.
, p. 1543 - 1553 (2008/10/08)
The unsolvated porphyrin compound (trifluoromethanesulfonato)(meso-tetraphenylporphinato)iron(III), [FeIII(TPP)(OSO2CF3)], has been structurally characterized by single-crystal X-ray diffraction in a monoclinic phase at 298 K and in a triclinic phase at 293 K and 188 K. While only one type of molecular site is found in the monoclinic phase, the temperature-dependent structural parameters and magnetic susceptibility data (5.82 μB at 293 K; 4.86 μB at 20 K) together indicate the existence of two crystallographically and magnetically distinct crystal lattice sites in the triclinic phase. One site of the triclinic phase (molecule 1) is unique in that its structure is temperature dependent, whereas the second spin-admixed site (molecule 2) has a structure which is essentially independent of temperature. This distinct site assignment has been further investigated by low-temperature Mo?ssbauer (6, 77, 150 K) and EPR (11 K) spectroscopy which suggest different spin ground states for molecules 1 and 2. As such, [FeIII(TPP)(OSO2CF3)] represents the first report of spin-state isomerism in the solid state for a pentacoordinate [FeIII(porphinato)X] species possessing two crystallographically, magnetically, and spectroscopically distinct sites in the same unit cell. This triclinic phase is also the first report of molecule pairs of the same porphyrin complex interacting in very different ways in the same crystal lattice, in that molecule 1 pairs form π-π dimers whereas molecule 2 pairs do not. Crystal data for [FeIII(TPP)(OSO2CF3)] in the monoclinic phase at 293 K: space group P21/a (No. 14), Z = 4, a = 14.249(4) A?, b = 17.630(4) A?, c = 15.175(5) A?, β = 97.35(3)°. Crystal data for [FeIII(TPP)(OSO2CF3)] in the triclinic phase: space group P1 (No. 2), Z = 4; a = 13.709(3) A?, b = 26.230(3) A?, c = 11.782(2) A?, α = 97.81(1)°, β = 114.84(2)°, and γ = 89.04(2)° at 293 K; a = 13.474(8) A?, b = 25.939(9) A?, c = 11.666(9) A?, α = 97.91(5)°, β = 114.28(5)°, and γ = 88.98(4)° at 188 K.
Multinuclear magnetic resonance spectroscopy of spin-admixed S = 5/2, 3/2 iron(III) porphyrins
Boersma, Arden D.,Goff, Harold M.
, p. 581 - 586 (2008/10/08)
A variety of synthetic iron(III) porphyrin complexes (FeIIIPorX, X = SO3CF3-, ClO4-, and C(CN)3-) were examined with multinuclear NMR spectroscopy (1H, 13C, 19F, and 35Cl). Deviations from NMR Curie law behavior, diminished magnetic moments, and characteristic ESR g = 4 values support previous evidence for the quantum-mechanical admixture of S = 5/2 and S - 3/2 states. NMR studies of titrations with the corresponding tetrabutylammonium salts and dipolar shift calculations show the ligands are coordinated rather than ion paired in solution. Solvent studies indicate more S = 5/2 character is present in aromatic solvents than in chlorinated solvents. Although the tricyanomethanide complex is thought to exhibit a "pure" S = 3/2 state in crystalline form, solution measurements are consistent with spin admixture.
Cytochrome Oxidase Models. 3. Spin Coupling across Imidazolate Bridges in Binuclear Metalloporphyrin Complexes of Iron and Copper
Dessens, Steven E.,Merrill, Connie L.,Saxton, Robert J.,Ilaria, Robert L.,Lindsey, John W.,Wilson, Lon J.
, p. 4357 - 4361 (2007/10/02)
Four new μ-imidazolato binuclear metalloporphyrin compounds of FeIII and CuII or ZnII have been synthesized, isolated, and characterized in the solid state as a model systems for the active of cytochrome c oxidase.The compounds have been derived from III(TPP)X> (X = Cl- or OSO2CF3-) and II(imidH)2DAP>2+ (M = Zn or Cu) to yield species containing the following μ-imidazolato cationic cores: III(imid)ZnII>+ (1), III(imid)CuII>+ (2), III(imid)ZnII>+ (3), and III(imid)CuII>+ (4).Comparative magnetochemical (15 300 K), Moessbauer (100 K), and EPR (10 K) studies of 1 and 2 are consistent with essentially identical electronic environments about FeIII (S = 1/2) with -JFeIII-CuII -1 in 2.Similar comparative studies of 3 and 4 are somewhat complicated by the presence of what appears to be two distinct molecular species of S = 5/2 and 1/2 coexisting in the same crystalline sample.The magnetic properties and silent EPr behavior of 4 have been rationalized in terms of a (S = 0, 2) mixture arising from strong antiferromagnetic coupling between FeIII (S = 1/2, 5/2) and CuII (S = 1/2), where -JFeIII-CuII >/ca. 200 cm-1.The implication of this result to the possible active-site structure of oxidase has been briefly considered.
