- MECHANISTIC CONSIDERATIONS IN THE PHOTODIPPROPORTIONATION OF μ-OXO-BIS ((TETRAPHENYLPORPHINATO)IRON(III))
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The photochemistry of μ-oxo-bis((tetraphenylporphinato)iron(III)) has been studied.Both continuous and photolysis establish a photochemical disproportionation to fom the ferrous complex FeTPP and the ferryl complex FeOTTP: Using triphenylphosp
- Peterson, Mark W.,Rivers, David S.,Richman, Robert M.
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- Electrochemistry and spectroscopy of sulfate and thiosulfate complexes of iron porphyrins
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The electrochemical and spectroscopic properties of the complex formed by the addition of thiosulfate to ferric porphyrins were examined. The NMR spectrum of the thiosulfate-ferric porphyrin complex was consistent with a high-spin ferric complex, while the EPR spectrum at liquid nitrogen temperatures indicated that the complex under these conditions was low-spin. Such behavior has been previously observed for other ferric porphyrin complexes. The visible spectra were characterized by a shift in the Soret band to higher energies, with smaller changes in the longer wavelength region. The complex was reasonably stable in DMF, but slowly reduced over several hours to FeII(TPP) and S4O62-. The voltammetric behavior of the thiosulfate complex in DMF consists of two waves, the first of which was irreversible. The ferric/ferrous reduction in the presence of thiosulfate was shifted negatively about 400 mV, compared to the Fe(TPP)(Cl) reduction. The visible, NMR and EPR spectra were most consistent with a Fe-S bonded ferric porphyrin-thiosulfate complex, Fe(P)(S-SO3)-. The kinetics of the reduction of ferric porphyrin by thiosulfate in DMSO indicated an autocatalytic mechanism, where the first step is the formation of the catalyst. The identity of the catalyst could not be determined because it must be present at low concentrations, but it is formed from the reaction of the ferric complex with thiosulfate. Coordination of thiosulfate to the porphyrin was not necessary for the reduction to occur, and the reduction of Fe(TPP)(Cl) by thiosulfate was accelerated by the addition of sulfate. Under these conditions, sulfate had replaced thiosulfate as the axial ligand for the ferric porphyrin. In the presence of sulfate, the reduction occurred in a single kinetic pseudo-first order step.
- Crawford, Philip W.,Ryan, Michael D.
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- Electronic configuration of five-coordinate high-spin pyrazole-ligated iron(II) porphyrinates
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Pyrazole, a neutral nitrogen ligand and an isomer of imidazole, has been used as a fifth ligand to prepare two new species, [Fe(TPP)(Hdmpz)] and [Fe(Tp-OCH3PP)(Hdmpz)] (Hdmpz = 3,5-dimethylpyrazole), the first structurally characterized example
- Hu, Chuanjiang,Noll, Bruce C.,Schulz, Charles E.,Scheidt, W. Robert
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- Hydrogen-Bonding Effects in Five-Coordinate High-Spin Imidazole-Ligated Iron(II) Porphyrinates
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The influence of hydrogen binding to the N-H group of coordinated imidazole in high-spin iron(II) porphyrinates has been studied. The preparation and characterization of new complexes based on [Fe(TPP)(2-MeHIm)] (TPP is the dianion of tetraphenylporphyrin) are reported. The hydrogen bond acceptors are ethanol, tetramethylene sulfoxide, and 2-methylimidazole. The last acceptor, 2-MeHIm, was found in a crystalline complex with two [Fe(TPP)(2-MeHIm)] sites, only one of which has the 2-methylimidazole hydrogen bond acceptor. This latter complex has been studied by temperature-dependent M?ssbauer spectroscopy. All new complexes have also been characterized by X-ray structure determinations. The Fe-NP and Fe-NIm bond lengths, and displacement of the Fe atom out of the porphyrin plane are similar to, but marginally different than, those in imidazole-ligated species with no hydrogen bond. All the structural and M?ssbauer properties suggest that these new hydrogen-bonded species have the same electronic configuration as imidazole-ligated species with no hydrogen bond. These new studies continue to show that the effects of hydrogen bonding in five-coordinate high-spin iron(II) systems are subtle and challenging to understand.
- Hu, Chuanjiang,Noll, Bruce C.,Schulz, Charles E.,Scheidt, W. Robert
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- Cyanide: A strong-field ligand for ferrohemes and hemoproteins?
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(Graph Presented) A CN weakling? The cyanide ligand in the five-coordinate iron(II) porphyrinate complex [Fe(tpp) (CN)]- (tpp= tetraphenylporphinato) is not a sufficiently strong-field ligand to cause the complex to be in the low-spin state under all conditions. Rather, the complex displays a reversible low-spin (LS) to high-spin (HS) crossover with no hysteresis.
- Li, Jianfeng,Lord, Richard L.,Noll, Bruce C.,Baik, Mu-Hyun,Schulz, Charles E.,Scheidt, W. Robert
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- Stable Iron Porphyrin Intramolecularly Coordinated by Alcoholate Anion: Synthesis and Evaluation of Axial Ligand Effect of Alcoholate on Spectroscopy and Catalytic Activity
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We synthesized intramolecularly aliphatic alcoholate-coordinated iron porphyrins (1a, 1b) that retain their axial coordination in the presence of another ligand or oxidant. The electron-donative character of alcoholate was less than that of thiolate, and
- Shirakawa, Yoshinori,Yano, Yuuki,Niwa, Yuki,Inabe, Kanako,Umezawa, Naoki,Kato, Nobuki,Hisamatsu, Yosuke,Higuchi, Tsunehiko
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- Just a proton: Distinguishing the two electronic states of five-coordinate high-spin iron(ll) porphyrinates with imidazole/ate coordination
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We report detailed studies on two S = 2 electronic states of high-spin iron(ll) porphyrlnates. These two states are exemplified by the five-coordinate derivatives with either neutral imidazole or anionic imidazolate as the axial ligand. The application of several physical methods all demonstrate distinctive differences between the two states. These Include characteristic molecular structure differences, Moessbauer spectra, magnetic circular dichroism spectroscopy, and Integer-spin EPR spectral distinctions. These distinctions are supported by DFT calculations. The two states are characterized by very different spatial properties of the doubly occupied orbital of the high-spin that are consonant with the physical properties.
- Hu, Chuanjiang,Sulok, Corinne D.,Paulat, Florian,Lehnert, Nicolai,Twigg, Anna I.,Hendrich, Michael P.,Schulz, Charles E.,Scheidt, W. Robert
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- Reactions of nitrogen oxides with heme models. Spectral and kinetic study of nitric oxide reactions with solid and solute FeIII(TPP)(NO 3)
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The reaction(s) of nitric oxide (nitrogen monoxide) gas with sublimed layers containing the nitrato iron(III) complex FeIII(TPP) (η2-O2NO) (1, TPP = meso-tetraphenyl porphyrinate 2-) leads to formation of several iron porphyrin species that are ligated by various nitrogen oxides. The eventual products of these low-temperature solid-state reactions are the nitrosyl complex Fe(TPP)(NO), the nitro-nitrosyl complex Fe(TPP)(NO2)(NO), and 1 itself, and the relative final quantities of these were functions of the NO partial pressure. It is particularly notable that isotope labeling experiments show that the nitrato product is not simply unreacted 1 but is the result of a series of transformations taking place in the layered material. Thus, the nitrato complex formed from solid Fe(TPP)(η2-O2NO) maintained under a 15NO atmosphere was found to be the labeled analogue Fe(TPP)(η2-O215NO). The reactivities of the layered solids are compared to the behaviors of the same species in ambient temperature solutions. To interpret the reactions of the labeled nitrogen oxides, the potential exchange reactions between N2O3 and 15NO were examined, and complete isotope scrambling was observed between these species under the reaction conditions (T = 140 K). Overall it was concluded from isotope labeling experiments that the sequence of reactions is initiated by reaction of 1 with NO to give the nitrato nitrosyl complex Fe(TPP)(η1-ONO2)(NO) (2) as an intermediate. This is followed by a reaction in the presence of excess NO that is equivalent to the loss of the nitrate radical NO3. to give Fe(TPP)(NO) as another transient species. A plausible pathway involving NO attack on the coordinated nitrate of 2 resulting in the release of N2O4 concerted with electron transfer to the metal center is proposed.
- Kurtikyan, Tigran S.,Gulyan, Gurgen M.,Martirosyan, Garik G.,Lim, Mark D.,Ford, Peter C.
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- Pyrolysis of Metalloporphyrins Part 1. - Fourier-transform Infrared Study of Fe-Tetraphenylporphyrin Chloride
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The pyrolysis of Fe-tetraphenylporphyrin chloride (FeClTPP) has been examined by FTIR spectroscopy.Two series of samples, with and without additional carbon black, were studied.It was found that the decomposition of FeClTPP occured in a very narrow range of temperature.The mixture of FeClTPP and carbon decomposed at a lower temperature than pure crystalline FeClTPP.The oxygen chemically adsorbed on the surface of carbon black may play an important role in this respect.The mechanism of pyrolysis have been discussed and a model of three steps of decomposition was proposed.The first step has been followed also by measuring the chlorine content by means of quantitative XPS.
- Sheng, Tai-Cheng,Rebenstorf, Bernd,Wideloev, Anders,Larsson, Ragnar
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- The surface trans effect: Influence of axial ligands on the surface chemical bonds of adsorbed metalloporphyrins
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The chemical bond between an adsorbed, laterally coordinated metal ion and a metal surface is affected by an additional axial ligand on the metal ion. This surface analogon of the trans effect was studied in detail using monolayers of various M(II)-tetrap
- Hieringer, Wolfgang,Flechtner, Ken,Kretschmann, Andreas,Seufert, Knud,Auwaerter, Willi,Barth, Johannes V.,Goerling, Andreas,Steinrueck, Hans-Peter,Gottfried, J. Michael
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- Photoreduction of ferric-tetraphenylporphyrin in oxygen-containing solvents revealed by resonance Raman and absorption spectroscopy
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Photoreduction is observed for Fe(III)(TPP)Cl (TPP is tetraphenylporphyrin) in some oxygen (O)-containing solvents under anaerobic conditions using resonance Raman (RR) and absorption spectroscopy. This process is found to be initiated by visible light in the 390-450 nm region. The coincidence of RR and absorption spectra of photoinduced species and of chemically reduced ones reveals that the final product of photoreduction is the high-spin Fe(II)(TPP)L complex, where L = THF (tetrahydrofuran), DMF(dimethyl formamide) or 1,4-dioxane. Such a photoreduction is not observed under anaerobic conditions for the Fe(III)(TPP)Cl complex in benzene, pyridine or CH2Cl2, nor in the abovementioned solvents under anaerobicconditions. No photoreduction is observed for Fe(III)(OEP)Cl (OEP = octaethylporphyrin). A mechanism for the photoinduced phenomenon observed for Fe(III)(TPP)Cl in O-containing solvents under anaerobic conditions isproposed.
- Terekhov, Sergei N.,Kruglik, Sergei G.
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- Copper-Dioxygen Reactivity Involved in the Formation of μ-oxoIII-O-CuIIL>+ Heterodinuclear Complexes (por = porphyrinate, L = tetradentate ligand), and Novel Synthesis of Square-Planar FeII(por) Species
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In the reaction of FeII(por) species with I(MeCN)>+ and O2 to give μ-oxoIII-O-CuIIL>+ 3 (por = porphyrinate, L = tetradentate ligand), copper-dioxygen adducts or their decomposition products must be present, otherwise III-OH> or III-O-FeIII(por)> products appear; a novel synthesis of square-planar FeII(por) is also described.
- Nanthakumar, Alaganandan,Fox, Stephen,Karlin, Kenneth D.
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- Metalloporphyrin photochemistry with matrix isolation
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The photochemistry of a number of metalloporphyrin oxoanion complexes has been examined by matrix isolation techniques, using both frozen solvent glasses and polymer films. After an extensive search for a noncoordinating, unreactive, glassing solvent, a 3:1 mixture of 2,2-dimethylbutane and tert-butylbenzene was found to work well at temperatures below 70 K. Alternatively, the photochemistry of metalloporphyrins was monitored in polymer films by the evaporation on a sapphire window of metalloporphyrin solutions in toluene containing either poly(methyl methacrylate) or poly(α-methylstyrene). The polymer films have the added advantage of a greatly increased temperature range, providing diffusional isolation even at room temperature. The photoreduction of the metal by homolytic α-bond cleavage and loss of the axial ligand appears to be a general mechanism for all metalloporphyrin complexes examined. The formation of metal-oxo species from photolysis of metalloporphyrin oxoanion complexes in solution derives from secondary, thermal reactions.
- Suslick, Kenneth S.,Bautista, Jocelyn F.,Watson, Randall A.
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- Iron porphyrin-catalyzed reduction of CO2. Photochemical and radiation chemical studies
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Several iron porphyrins have been reduced by photochemical and radiation chemical methods, in organic solvents and in aqueous solutions, from FeIIIP to FeIIP to FeIP and beyond. In aqueous solutions, the FeIP state is relatively stable for the tetrakis(N-methyl-2-pyridyl)porphyrin at high pH but is shorter lived in neutral and acidic solutions. The FeIP state of tetrakis(N-methyl-3-pyridyl)porphyrin and tetrakis(N-methyl-4-pyridyl)-porphyrin are short-lived at any pH. Decay of FeIP is accelerated by H+ and by CO2, probably via reaction with the Fe0P state formed upon disproportionation of FeIP. These reactions may lead to formation of H2 and CO, respectively, and to formation of the chlorin, FeIIPH2, as a side product. The FeIP state is also observed as a stable product in several organic solvents. This is observed by photolysis of iron tetraphenylporphyrin and several of its derivatives (e.g., trimethyl-, dichloro- and pentafluorophenyl), mainly in dimethylformamide and acetonitrile solutions, using triethylamine as a reductive quencher. Further photoreduction in the presence of CO2 results in catalyzed reduction of CO2 to CO and formation of (CO)-FeIIP. The yield of free CO increases with time of photolysis and reaches turnover numbers of approximately 70 molecules of CO per porphyrin molecule.
- Grodkowski,Behar,Neta,Hambright
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- Experimental and Theoretical Evidence for an Unusual Almost Triply Degenerate Electronic Ground State of Ferrous Tetraphenylporphyrin
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Iron porphyrins exhibit unrivalled catalytic activity for electrochemical CO2-to-CO conversion. Despite intensive experimental and computational studies in the last 4 decades, the exact nature of the prototypical square-planar [FeII(TPP)] complex (1; TPP2- = tetraphenylporphyrinate dianion) remained highly debated. Specifically, its intermediate-spin (S = 1) ground state was contradictorily assigned to either a nondegenerate 3A2g state with a (dxy)2(dz2)2(dxz,yz)2 configuration or a degenerate 3Egθ state with a (dxy)2(dxz,yz)3(dz2)1/(dz2)2(dxy)1(dxz,yz)3 configuration. To address this question, we present herein a comprehensive, spectroscopy-based theoretical and experimental electronic-structure investigation on complex 1. Highly correlated wave-function-based computations predicted that 3A2g and 3Egθ are well-isolated from other triplet states by ca. 4000 cm-1, whereas their splitting ΔA-E is on par with the effective spin-orbit coupling (SOC) constant of iron(II) (≈400 cm-1). Therfore, we invoked an effective Hamiltonian (EH) operating on the nine magnetic sublevels arising from SOC between the 3A2g and 3Egθ states. This approach enabled us to successfully simulate all spectroscopic data of 1 obtained by variable-temperature and variable-field magnetization, applied-field 57Fe M?ssbauer, and terahertz electron paramagnetic resonance measurements. Remarkably, the EH contains only three adjustable parameters, namely, the energy gap without SOC, ΔA-E, an angle θ that describes the mixing of (dxy)2(dxz,yz)3(dz2)1 and (dz2)2(dxy)1(dxz,yz)3 configurations, and the ?rd-3?expectation value of the iron d orbitals that is necessary to estimate the 57Fe magnetic hyperfine coupling tensor. The EH simulations revealed that the triplet ground state of 1 is genuinely multiconfigurational with substantial parentages of both 3A2g (12%), owing to their accidental near-triple degeneracy with ΔA-E = +950 cm-1. As a consequence of this peculiar electronic structure, 1 exhibits a huge effective magnetic moment (4.2 μB at 300 K), large temperature-independent paramagnetism, a large and positive axial zero-field splitting, strong easy-plane magnetization (g⊥ ≈ 3 and g∥ ≈ 1.7) and a large and positive internal field at the 57Fe nucleus aligned in the xy plane. Further in-depth analyses suggested that g⊥ ? g∥ is a general spectroscopic signature of near-triple orbital degeneracy with more than half-filled pseudodegenerate orbital sets. Implications of the unusual electronic structure of 1 for CO2 reduction are discussed.
- Tarrago, Maxime,R?melt, Christina,Nehrkorn, Joscha,Schnegg, Alexander,Neese, Frank,Bill, Eckhard,Ye, Shengfa
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- Macrocycle- And metal-centered reduction of metal tetraphenylporphyrins where the metal is copper(ii), nickel(ii) and iron(ii)
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The reduction of metal(ii) tetraphenylporphyrins, where metal(ii) is copper, nickel or iron, has been performed in toluene solution in the presence of a cryptand. Cesium anthracenide was used as a reductant. Crystalline salts {cryptand(Cs+)}2{CuII(TPP4-)}2- (1) and {cryptand(Cs+)}{NiI(TPP2-)}-·C6H5CH3 (2) have been obtained. The two-electron reduction of {CuII(TPP2-)}0 is centered on the macrocycle allowing one to study for the first time the structure and properties of the TPP4- tetraanions in the solid state. Tetraanions have a diamagnetic state and show essential C-Cmeso bond alternation. New bands attributed to TPP4- appear at 670, 770 and 870 nm. Unpaired S = 1/2 spin is localized on CuII. The one-electron reduction of {NiII(TPP2-)}0 centered on nickel provides the formation of {NiI(TPP2-)}- with unpaired S = 1/2 spin localized on NiI at 100(2) K. The effective magnetic moment of 2 is 1.68μB at 120 K and a broad asymmetric EPR signal characteristic of NiI is observed for 2 and also for (Bu3MeP+){NiI(TPP2-)}-·C6H5CH3 (3) in the 4.2-120 K range. Since dianionic TPP2- macrocycles are present at 100(2) K, no alternation of C-Cmeso bonds is observed in 2. The excited quartet S = 3/2 state according to the calculations is positioned close to the ground S = 1/2 state. In the excited state, charge transfer from NiI to the macrocycle takes place resulting in the formation of NiII with S = 1 and TPP3- with S = 1/2 in the {NiII(TPP3-)}- anions. Therefore, the increase in the magnetic moment of 2 above 150 K is attributed to the population of the excited quartet state with a gap of 750 K. Salt 2 is EPR silent above 150 K and manifests absorption bands characteristic of TPP3- at RT. The reduction of NiII(TPP2-) and FeII(TPP2-) by cesium anthracenide in the presence of Bu3MeP+ yields crystals of 3 and (Bu3MeP+){FeI(TPP2-)}-·C6H5CH3 (4) whose crystal structures and optical properties are also presented. DFT calculations have been carried out for {MII(TPP2-)} (M = Cu, Ni and Fe) and their anions to interpret the experimental results obtained for 1-4. This journal is
- Andronov, Mikhail G.,Khasanov, Salavat S.,Kitagawa, Hiroshi,Konarev, Dmitri V.,Kuzmin, Aleksey V.,Nazarov, Dmitry I.,Otsuka, Akihiro,Shestakov, Alexander F.,Yamochi, Hideki,Yudanova, Evgeniya I.
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p. 15620 - 15632
(2021/12/02)
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- Efficient oxidation of cumene to cumene hydroperoxide with ambient O2 catalyzed by metalloporphyrins
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A novel and efficient protocol for oxidation of cumene to cumene hydroperoxide was presented using ambient O2 catalyzed by very simple metalloporphyrins. The selectivity toward cumene hydroperoxide reached 98.3% in the cumene conversion of 28.1% with T(4-COOH)PPCu as a catalyst at 80°C. The origin of the higher performance of T(4-COOH)PPCu was mainly ascribed to the low catalytic performance of copper(II) in the cumene hydroperoxide decomposition, and the ability of T(4-COOH)PP in stabilizing cumene hydroperoxide through hydrogen-bond interactions between them. Compared with current industrial processes and academic research in oxidation of cumene to cumene hydroperoxide with O2, the main superiorities of this protocol were the high selectivity, high conversion, simple catalysts, solvent-free, additive-free and mild conditions which made this work an appealing reference for the industrial oxidation of cumene to cumene hydroperoxide, as well as the oxidative functionalization of other C-H bonds in various hydrocarbons. 2021 World Scientific Publishing Company.
- Shen, Hai M.,Ye, Hong L.,Wang, Qin,Hu, Meng Y.,Liu, Lei,She, Yuan B.
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p. 314 - 322
(2021/04/09)
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- Selective nitrogen reduction to ammonia on iron porphyrin-based single-site metal-organic frameworks
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Constructing efficient catalysts for N2reduction into value added ammonia under ambient conditions is a considerable challenge. Herein, well-defined single-site metal-organic frameworks (MOFs, M-TCPP; M = Fe, Co, or Zn) were constructed and evaluated as electrocatalysts for N2reduction. The prepared Fe-TCPP exhibited prominent performance with a high NH3yield of 44.77 μg h?1mgcat.?1and a faradaic efficiency of 16.23%, superior to that of all the reported molecular and MOF catalysts. The superior performance was ascribed to the highly effective N2activation at the Fe site, and benefited from the overall reaction thermodynamics advantage in the key reaction step of *NNH formation. This study gives an understanding of the intrinsic activity of well-defined catalysts in the electrocatalytic N2reduction, and provides atomic-level insights into the rational design and engineering of highly active catalysts for artificial N2fixation.
- Cong, Meiyu,Chen, Xuyang,Xia, Kai,Ding, Xin,Zhang, Linlin,Jin, Yu,Gao, Yan,Zhang, Lixue
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supporting information
p. 4673 - 4678
(2021/03/09)
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- Mechanism of Catalytic O2 Reduction by Iron Tetraphenylporphyrin
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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.
- 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.
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supporting information
p. 8315 - 8326
(2019/06/04)
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- Iron(II)-Based Metalloradical Activation: Switch from Traditional Click Chemistry to Denitrogenative Annulation
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A unique concept for the intermolecular denitrogenative annulation of 1,2,3,4-tetrazoles and alkynes was discovered by using a catalytic amount of Fe(TPP)Cl and Zn dust. The reaction precludes the traditional, more favored click reaction between an organic azide and alkynes, and instead proceeds by an unprecedented metalloradical activation. The method is anticipated to advance access to the construction of important basic nitrogen heterocycles, which will in turn enable discoveries of new drug candidates.
- Roy, Satyajit,Khatua, Hillol,Das, Sandip Kumar,Chattopadhyay, Buddhadeb
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supporting information
p. 11439 - 11443
(2019/07/17)
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- Metalloporphyrin complex and organic electroluminescent device thereof
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The invention provides a metalloporphyrin complex and an organic electroluminescent device thereof, and belongs to the technical field of organic photoelectric materials. The invention discloses a metalloporphyrin complex, which contains a porphyrin-conta
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Paragraph 0048; 0050; 0053; 0054
(2020/01/08)
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- Comparative FTIR study of the cobalt and iron porphyrin reactions with CO. Does cobalt porphyrin form a bis-carbonyl complex in the Ar matrix?
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The adducts of Co(II)(TPP) and Fe(II)TPP (TPP is meso-tetraphenyl-porphyrinato dianion) with carbon monoxide in Ar matrix at 10 K have been studied by FTIR spectroscopy using CO, C18O and their equimolar mixture. It is shown that both metals ma
- Martirosyan,Adonts,Hovhannisyan,Kurtikyan
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- Electronic Structure and Spin Multiplicity of Iron Tetraphenylporphyrins in Their Reduced States as Determined by a Combination of Resonance Raman Spectroscopy and Quantum Chemistry
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Iron tetraphenylporphyrins are prime candidates as catalysts for CO2 reduction. Yet, even after 40 years of research, fundamental questions about the electronic structure of their reduced states remain, in particular as to whether the reducing equivalents are stored at the iron center or at the porphyrin ligand. In this contribution, we address this question by a combination of resonance Raman spectroscopy and quantum chemistry. Analysis of the data allows for an unequivocal identification of the porphyrin as the redox active moiety. Additionally, determination of the spin state of iron is possible by comparing the characteristic shifts of spin and oxidation-state-sensitive marker bands in the Raman spectrum with calculations of planar porphyrin model structures.
- R?melt, Christina,Ye, Shengfa,Bill, Eckhard,Weyhermüller, Thomas,Van Gastel, Maurice,Neese, Frank
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supporting information
p. 2141 - 2148
(2018/02/27)
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- Solventless mechanochemical metallation of porphyrins
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A fast solvent-free method for the metallation of porphyrins is presented. ZnTPP, NiTPP, CuTPP and FeTPP have been prepared mechanochemically by ball milling hydrated metal acetate salts with meso-tetraphenylporphyrin (H2TPP) in a shaker mill for as little as 20 min with no added solvent, avoiding the need for undesirable solvents and long reaction times normally used in such reactions.
- Ralphs, Kathryn,Zhang, Chen,James, Stuart L.
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supporting information
p. 102 - 105
(2017/08/14)
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- Electronic Structure of a Formal Iron(0) Porphyrin Complex Relevant to CO2 Reduction
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Iron porphyrins can act as potent electrocatalysts for CO2 functionalization. The catalytically active species has been proposed to be a formal Fe(0) porphyrin complex, [Fe(TPP)]2- (TPP = tetraphenylporphyrin), generated by two-electron reduction of [FeII(TPP)]. Our combined spectroscopic and computational investigations reveal that the reduction is ligand-centered and that [Fe(TPP)]2- is best formulated as an intermediate-spin Fe(II) center that is antiferromagnetically coupled to a porphyrin diradical anion, yielding an overall singlet ground state. As such, [Fe(TPP)]2- contains two readily accessible electrons, setting the stage for CO2 reduction.
- R?melt, Christina,Song, Jinshuai,Tarrago, Maxime,Rees, Julian A.,Van Gastel, Maurice,Weyhermüller, Thomas,Debeer, Serena,Bill, Eckhard,Neese, Frank,Ye, Shengfa
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supporting information
p. 4745 - 4750
(2017/04/26)
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- Biomimetic Nitration of Phenols Using Metalloporphyrins/H2O2/NO2 -
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An efficient metalloporphyrins/H2O2/NO2 - nitration of phenols has been developed. The total yield of nitrophenol could reach up to 55.1 %, which is about 4 and sixfold higher than that of horse radish peroxidase catalysis and peroxynitrite nitration, respectively. Furthermore, the nitration system attained an enhanced regioselectivity of 1.0 o/p ratio, and exhibited a good substrate scope of monophenols. This protocol is environmentally friendly compared with HNO3/H2SO4 nitration, and stable, inexpensive and organic solvent tolerant compared with enzyme catalytic nitration and peroxynitrite nitration reaction. Graphical Abstract: [Figure not available: see fulltext.]
- Sun, Weizhi,Liu, Yaojie,Zhang, Haibo,Xian, Mo,Liu, Huizhou
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p. 1991 - 1999
(2015/12/24)
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- Studies of iron(III) porphyrinates containing silanethiolate ligands
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The chemistry of several iron(III) porphyrinates containing silanethiolate ligands is described. The complexes are prepared by protonolysis reactions of silanethiols with the iron(III) precursors, [Fe(OMe)(TPP)] and [Fe(OH)(H 2O)(TMP)] (TPP = dianion of meso-tetraphenylporphine; TMP = dianion of meso-tetramesitylporphine). Each of the compounds has been fully characterized in solution and the solid state. The stability of the silanethiolate complexes versus other iron(III) porphyrinate complexes containing sulfur-based ligands allows for an examination of their reactivity with several biologically relevant small molecules including H2S, NO, and 1-methylimidazole. Electrochemically, the silanethiolate complexes display a quasi-reversible one-electron oxidation event at potentials higher than that observed for an analogous arenethiolate complex. The behavior of these complexes versus other sulfur-ligated iron(III) porphyrinates is discussed.
- Meininger, Daniel J.,Caranto, Jonathan D.,Arman, Hadi D.,Tonzetich, Zachary J.
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p. 12468 - 12476
(2013/11/19)
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- Five- and six-coordinate adducts of nitrosamines with ferric porphyrins: Structural models for the type II interactions of nitrosamines with ferric cytochrome P450
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Nitrosamines are well-known for their toxic and carcinogenic properties. The metabolic activation of nitrosamines occurs via interaction with the heme-containing cytochrome P450 enzymes. We report the preparation and structural characterization of a number of nitrosamine adducts of synthetic iron porphyrins. The reactions of the cations [(por)Fe(THF)2]ClO 4 (por = TPP, TTP, OEP) with dialkylnitrosamines (R2NNO; R2 = Me2, Et2, (cyclo-CH2) 4, (cyclo-CH2)5, (PhCH2) 2) in toluene generate the six-coordinate high-spin (S = 5/2) [(por)Fe(ONNR2)2]ClO4 compounds and a five-coordinate intermediate-spin (S = 3/2) [(OEP)Fe(ONNMe2)]ClO 4 derivative in 57-72% yields (TPP = 5,10,15,20- tetraphenylporphyrinato dianion, TTP = 5,10,15,20-tetra-p-tolylporphyrinato dianion, OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato dianion). The N-O and N-N vibrations of the coordinated nitrosamine groups in [(por)Fe(ONNR 2)2]ClO4 occur in the 1239-1271 cm-1 range. Three of the six-coordinate [(por)Fe(ONNR2) 2]ClO4 compounds and one five-coordinate [(OEP)Fe(ONNMe2)]ClO4 compound have been characterized by single crystal X-ray crystallography. All the nitrosamine ligands in these complexes bind to the ferric centers via a sole η1-O binding mode. No arylnitrosamine adducts were obtained from the reactions of the precursor compounds [(por)Fe(THF)2]ClO4 with three arylnitrosamines (Ph2NNO, Ph(Me)NNO, Ph(Et)NNO). However, prolonged exposure of [(por)Fe(THF)2]ClO4 to these arylnitrosamines resulted in the formation of the known five-coordinate (por)Fe(NO) derivatives. The latter (por)Fe(NO) compounds were obtained more readily by the reactions of the three arylnitrosamines with the four-coordinate (por)FeII precursors.
- Xu, Nan,Goodrich, Lauren E.,Lehnert, Nicolai,Powell, Douglas R.,Richter-Addo, George B.
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experimental part
p. 4405 - 4419
(2010/07/04)
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- Six-coordinate nitro complexes of iron(III) porphyrins with trans S-donor ligands. Oxo-transfer reactivity in the solid state
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Spectroscopic studies demonstrate that the 5-coordinate O-nitrito complexes Fe(Por)(η1-ONO) (Por - mesotetraphenyl- or meso-tetra-p-tolyl- porphyrinato dianions) react with the thioethers (R2S) dimethylsulfide and tetrahydrothiophene
- Kurtikyan, Tigran S.,Hovhannisyan, Astghik A.,Iretskii, Alexei V.,Ford, Peter C.
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p. 11236 - 11241
(2010/03/04)
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- Interaction of nitrogen bases with iron-porphyrin nitrito complexes Fe(Por)(ONO) in sublimed solids
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The reactions of the nitrogen Lewis bases (B) 1-methylimidazole (1-Melm), pyridine (Py), and NH3 as gases with sublimed layers containing the 5-coordinate nitrito iron(III)-porphyrinato complexes Fe(Por)(η1- ONO) (1) are described (P
- Kurtikyan, Tigran S.,Hovhannisyan, Astghik A.,Gulyan, Gurgen M.,Ford, Peter C.
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p. 7024 - 7031
(2008/10/09)
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- Reactions of nitrogen oxides with heme models: Spectral characterization of an elusive five-coordinate FeIII(porphyrin) nitrito intermediate
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(Chemical Equation Presented) The famous five: The elusive five-coordinate nitrito complexes [FeIII(por)(ONO)] (por = meso- tetraphenylporphyrinato dianion or meso-tetra-p-tolylporphyrinato dianion) have been obtained by interaction of low-pres
- Kurtikyan, Tigran S.,Ford, Peter C.
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p. 492 - 496
(2007/10/03)
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- Electronic configuration assignment and the importance of low-lying excited states in high-spin imidazole-ligated iron(II) porphyrinates
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The synthesis and characterization of six new high-spin deoxymyoglobin models (imidazole-(tetraarylporphyrinato)iron(II)) are described. These have been intensively studied by temperature-dependent Moessbauer spectroscopy from 295 to 4.2 K. All complexes
- Hu, Chuanjiang,Roth, Arne,Ellison, Mary K.,An, Jin,Ellis, Christina M.,Schulz, Charles E.,Scheidt, W. Robert
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p. 5675 - 5688
(2007/10/03)
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- Heme carbonyls: Environmental effects on vc-o and Fe-C/C-O bond length correlations
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The synthesis and characterization of four low-spin (carbonyl)iron(11) tetraphenylporphyrinates, [Fe(TPP)(CO)(L)], where L = 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole (unsolvated), and 1,2-dimethylimidazole (toluene solvate) are reported. The complexes show nearly the same value of vc-o in toluene solution (1969-72 cm-1) but a large range of CO stretching frequencies in the solid-state (1926-1968 cm-1). The large solid-state variation results from CO interactions in the solid state, as shown by an examination of the crystal structures of the four complexes. The high precision of the four structures obtained allows us to make a number of structural and spectroscopic correlations that describe the Fe-C-O and N lm-Fe-CO units. The values of vc-o and the Fe-C and C-O bond distances are strongly correlated and provide a structural, as well as a spectroscopic, correlation of the π back-bonding model. The interactions of CO described are closely related to the large range of CO stretching frequencies observed in heme proteins and specific interactions observed in carbonylmyoglobin (MbCO).
- Silvernail, Nathan J.,Roth, Arne,Schulz, Charles E.,Noll, Bruce C.,Scheldt, W. Robert
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p. 14422 - 14433
(2007/10/03)
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- Structure of the deoxymyoglobin model [Fe(TPP)(2-MeHIm)] reveals unusual porphyrin core distortions
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The preparation and characterization of the deoxymyoglobin model (2-methylimidazole)(tetraphenylporphinato)iron-(II) is described. The preparation and crystallization from chlorobenzene leads to a new crystalline phase that has been structurally character
- Ellison, Mary K.,Schulz, Charles E.,Scheidt, W. Robert
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p. 2173 - 2181
(2008/10/08)
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- Electroreduction of μ-oxo iron(III) porphyrins adsorbed on an electrode leading to a cofacial geometry for the iron(II) complex: Unexpected active site for the catalytic reduction of O2 to H2O
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Acidification of a solution of (μ-oxo)bis[(5,10,15,20- tetraphenylporphyrinato)iron(III)] ([{Fe(tpp)}2O], II) in CH2Cl2 produced equimolar amounts of a hydroxoiron(III) complex [(tpp)Fe(III)(OH)] (III) and an iron(III) complex [(tpp)Fe(III)(ClO4)] (IV). The complex IV was isolated as a perchlorate salt, which crystallized in the triclinic space group P1 (2); a = 11.909(3), b = 19.603(4), c = 10.494(3) A, α = 95.74(2)°, β = 107.91(2)°, γ = 89.14(2)°, V = 2319.1(9) A3, Z = 2, D(calc)= 1.328 g cm-3, μ(Mo Kα) = 4.35 cm-1, final R = 0.055 and R(w) = 0.050. The crystal structure of IV revealed that ClO4- is coordinated to the iron atom, which may be driven by the preference of iron(III) to be five coordinate rather than four coordinate. Reduction of the complex II in the presence of acid by electrolysis and/or by a reducing agent, such as sodium dithionite, under argon produced [Fe(II)(tpp)]. The addition of O2 to a solution of [Fe(tpp)] in acidic CH2Cl2 in the presence of an equimolar amount of the reducing agent produced the complex III. When the complex II was adsorbed on an electrode surface and placed in aqueous acidic electrolyte solutions, electroreduction of the adsorbate proceeded according to the half- reaction: [{Fe(tpp)}2O] +2H++2e-→2[Fe(tpp)]+H2O, at 0.031-0.059 pH V (vs. SCE, pH > 1.0). Based on these results, oxo-bridged iron(III) porphyrin dimers were used as electrocatalysts for the reduction of O2. The catalytic reduction of O2 proceeded at potentials in the vicinity of those for II. As a whole, the proportion of H2O as the product increased from 50% for adsorbed [(tpp)Fe(III)Cl] to > 90% for the adsorbed dimer. Thus, electroreduction of the dimer adsorbed on a carbon electrode immersed in aqueous acid produced two solid state, cofacially fixed iron(II) porphyrin molecules: [PFe(III)OFe(III)P](ad)+2H++2e-→[PFe(II) Fe(II)P](ad)+H2O (P = porphyrin dianion). Coordination of molecular oxygen to the adjacent two iron(II) centers under acidic conditions allowed formation of O2-bridged iron(III) porphyrin [PFe(III)(O2) Fe(III)P](ad) at the electrode surface. Electroreduction of the adsorbate under acidic conditions produced H2O and allowed the reformation of [PFe(II) Fe(II)P](ad). The implication is that the electroreduction of the adsorbed oxo-bridged dimer gives a cofacial geometry for PFe(II) on the electrode, facilitating the coordination and subsequent splitting of O2.
- Oyaizu, Kenichi,Haryono, Agus,Natori, Junichiro,Shinoda, Hiroshi,Tsuchida, Eishun
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p. 1153 - 1163
(2007/10/03)
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- Carbonyl complexes of iron(II), ruthenium(II), and osmium(II) 5,10,15,20-tetraphenylporphyrinates: A comparative investigation by x-ray crystallography, solid-state NMR spectroscopy, and density functional theory
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We have synthesized and characterized via single-crystal X-ray diffraction methods iron(II), ruthenium(II), and osmium(II) carbonyl derivatives of (1-methylimidazole)(5,10,15,20- tetraphenylporphyrinate)[(5,10,15,20-tetraphenylporphyrinate = TPP)], Fe(TPP)(CO)(1-MeIm)·toluene, Ru(TPP)(CO)(1-MeIm)·chloroform, and Os(TPP)(CO)(1-MeIm)·chloroform, together with the osmium(II) pyridine adduct Os(TPP)-(CO)(py)·2benzene. The crystallographic results permit a detailed structural comparison between all of the six carbonyl metalloporphyrins which can be prepared from TPP, Fe, Ru, Os, and the two axial bases 1- methylimidazole and pyridine. The structures of all three (Fe, Ru, Os) 1- methylimidazole complexes display major saddle distortions, with the extent of the distortions being Fe > Ru ~ Os. For the pyridine complexes, deviations from planarity of the porphyrin ring are about an order of magnitude smaller than those for the 1-methylimidazole species. The M-C-O bond angles in all complexes are in the range 176.8-179.3°. We also determined the 13C and 17O NMR isotropic chemical shifts, the 13C NMR chemical shift tensor elements, and, for the three 1-MeIm adducts, the 17O nuclear quadruple coupling constants. We then used density functional theory (DFT) to relate the experimental spectroscopic results to the experimental structures. For the 13C and 17O isotropic shifts, there are excellent correlations between theory and experiment (13C, R2 value = ~0.99; 17O, R2 value = ~.99), although the slopes (13C, ~-0.97; 17O, ~-1.27) deviate somewhat from the ideal values. For the 17O nuclear quadruple coupling constant, our results indicate an rms error between theory and experiment of 0.20 MHz, for experimental values ranging from (+)1.0 to (- )0.40 MHz, where the signs are deduced from the calculations. The ability to predict spectroscopic observables in metalloporphyrin systems having relatively well characterized structures by using density functional theory provides additional confidence in the application of these theoretical methods to systems where structures are much less certain, such as heme proteins.
- Salzmann, Renzo,Ziegler, Christopher J.,Godbout, Nathalie,McMahon, Michael T.,Suslick, Kenneth S.,Oldfield, Eric
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p. 11323 - 11334
(2007/10/03)
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- Photochemical activation of metalloporphyrin carbene complexes
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While the photochemistry of simple metalloporphyrin complexes has been explored to some extent, the photoactivation of multiple-bonded axial ligands coordinated to metalloporphyrins has not been previously examined. We report here the photochemistry of several iron porphyrin carbene and vinylidene complexes. Irradiation of these complexes with visible light cleaves the iron-carbon double bond and produces a four coordinate iron(II) porphyrin and a free carbene, which can be trapped in high yield with a variety of alkenes. This photochemistry is unique among organo transition metal complexes of carbenes or alkylidenes. For these metalloporphyrin carbene complexes, the presence of the porphyrin ring alters the photoreactivity of the metal-carbon bond. This is probably due to the mixing between the π * orbitals of the porphyrin ring and the iron-carbon orbitals, which is also responsible for the hypso-type spectrum (i.e. blue-shifted) seen in these complexes. Hypso spectra are a common trait in other photodissociative porphyrin complexes, most notably CO complexes.
- Ziegler, Christopher J.,Suslick, Kenneth S.
-
-
- Kinetics, mechanism and thermodynamics of iron carbon bond dissociation in organoiron porphyrin complexes
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Thermolysis of Fe(P)R (P = octaethylporphyrinato dianion, R = C6H5, CH3, C2H5, CH2C(CH3)3; P = tetraphenylporphyrinato dianion, R = C6H5; P = tet
- Riordan, Charles G.,Halpern, Jack
-
-
- (1)H NMR spectra and electronic structure of reduced iron porphyrins: Fe(II), Fe(I) and Fe(0) porphyrins
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Fe(II), Fe(I) and Fe(0) porphyrins have been generated by stepwise reduction with a sodium mirror in vacuum and their (1)H NMR spectra have been recorded and analyzed.Fe(II) porphyrins (Fe(II)P) have been examined in three spin states, an S = 0 state in pyridine-d8, an S = 1 state in benzene-d6 and an S = 2 state in tetrahydrofuran-d8 (THF-d8).The analysis of isotropic shifts for low-spin Fe(II)P (S = 0) has indicated that no charge transfer has been observed.The ground state configuration is (dxy)2(dxz,dyx)4.The contact shifts for intermediate-spin Fe(II)P (S = 1) reflect P -> Fe ? charge transfer.The proposed electron configuration is (dxy)2 (dz2)2 (dxz,dyz)2, which agrees with Moessbauer data.The pattern of contact shifts for high-spin Fe(II)P (S = 2) is consistent with ? spin transfer, which suggests that the d(x2-y2) orbital possesses an unpaired spin.The electron configuration is (dxy)2 (dxz,dyz)2 (dz2)1 (d(x2-y2))1.Our results for Fe(II)P (S = 1,2) agree with the literature (1)H NMR data.In the case of Fe(I)P in THF, the separation of isotropic shifts into the dipolar and contact contributions has shown the dominance of the latter.The observed shifts indicate negative ? spin density on pyrrole and meso carbon atoms of the ligand, which seems to be due to a strong ?-? spin polarization effect.When this fact is taken into account the pattern of contact shifts is consistent with ? spin transmission involving both P -> Fe ? charge transfer out of the ligand-filled molecular (3e(?)) orbital and Fe -> P ?* charge transfer into the ligand highest unoccupied (4e(?*)) molecular orbital.The occurrence of the unpaired spin in this molecular orbital is consistent with ?-radical anion formulation which was found by X-ray crystallography.An S = 1/2 spin state determined by magnetic moment measurements agrees with the most probable electron configuration (dxy)2 (dxz,dyz)3 (dz2)2.In the case of Fe(0)P, the isotropic shifts were found to be small, providing evidence of some spin transfer.The ground state configuration is (dxy)2 (dxz,dyz)4 (dz2)2.
- Sinyakov, G.N.,Shulga, A.M.
-
-
- Photochemical reduction of nitrate and nitrite by manganese and iron porphyrins
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New nitrate and nitrite complexes of metalloporphyrins have been synthesized and crystallographically characterized, and their photochemistry has been examined. Irradiation of Mn(TPP)(NO3) and Mn(TPP)(NO2) (where TPP = 5,10,15,20-tetraphenylporphyrinate(2-)) produces the high-valent metal-oxo species O=MnIV(TPP) quantitatively, with quantum yields of 1.58 × 10-4 and 5.30 × 10-4, respectively. This metal-oxo species is capable of oxidizing substrates, as demonstrated in reactions with styrene or triphenylphosphine. Mn(TPP)(NO2) is formed as an intermediate in the complete photolysis of Mn(TPP)(NO3). Similarly, the photochemistry of Fe(TPP)(NO3) produces substrate oxidation, including C-H hydroxylation, which suggests the photochemical formation of O=FeIV(TPP.+) as the active oxidant. Remarkably, all three oxygen atoms of the initially bound NO3- can be used for substrate oxidation. The X-ray crystal structures of Mn(TPP)(NO3)·2C6H6 and Mn(TPP)(NO2)·C6H6 have been solved. In the nitrate complex Mn(TPP)(NO3), the average Mn-pyrrole N distance is 2.007 A?, with the metal 0.21 A? above the mean plane of the nitrogen atoms. The nitrate ion is coordinated in a unidentate fashion with a Mn-O bond length of 2.101 A?. Mn(TPP)(NO2) is the first metalloporphyrin complex with oxygen-bound nitrite. The average Mn-pyrrole nitrogen distance is 2.012 A?, with the metal 0.23 A? above the mean plane of the nitrogen atoms. The nitrite ion is coordinated through one of the oxygens, with a Mn-O bond length of 2.059 A?. Crystal data for Mn(TPP)(NO3)·2C6H6 at -76°C: space group P1, a = 13.271 (4) A?, b = 13.610 (5) A?, c = 12.880 (3) A?, α = 111.44 (2)°, β = 95.71 (2)°, γ = 85.50 (3)°, V = 2152 (2) A?3, Z = 2, RF = 0.063, RwF = 0.086 for 408 variables and 4890 unique data with I > 2.58σ(I). Crystal data for Mn(TPP)(NO2)·C6H6: space group Pccn, a = 21.631 (11) A?, b = 19.941 (12) A?, c = 17.991 (6) A?, V = 7760 (7) A?3, Z = 8, RF = 0.062, RwF = 0.096 for 543 variables and 3820 unique data with I > 2.58σ(I).
- Suslick, Kenneth S.,Watson, Randall A.
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p. 912 - 919
(2008/10/08)
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- Resonance raman spectra of reaction intermediates in the oxidation process of ruthenium(II) and iron(II) porphyrins
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The dioxo ruthenium porphyrins, RuP(O)2 (P = TPP and TMP), were prepared by the oxidation of RuP(CO) with m-chloroperoxybenzoic acid (m-CPBA). The resonance Raman and IR spectra of RuP(O)2 were measured and their O=Ru=O vibrations in
- Paeng,Nakamoto
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p. 3289 - 3297
(2007/10/02)
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- Photochemistry of Nitrosyl Porphyrins in the Temperature Range 180-300 K and the Effects of Pyridine on Photodenitrosylation of Nitrosyliron Tetraphenylporphyrin
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Nitrosylmetal tetraphenylporphyrin (NOMTPP, M=Fe,Co, and Mn) in benzene solutions undergoes facile photodenitrosylation to give NO and metal(II) tetraphenylporphyrin, MIITPP.The photodenitrosylation yields of NOFeTPP and NOCoTPP are respectively determined as 0.50 +/- 0.05 and 1.0 +/- 0.05 at both excitation wavelengths 355 and 532 nm.The yield, Φ, in toluene is expressed as a function of temperature: Φ = (1 + 1.56 x 10-2 exp(2400/RT))-1 for NOFeTPP and Φ = (1 + 1.02 x 10-6 exp(5200/RT))-1 for NOCoTPP.Contrary to NOFeTPP and NOCoTPP, the photodenitrosylation yields, Φ, of NOMnTPP are independent of temperature in the range 300-180 K and exhibit excitation wavelength dependence: Φ = 0.78 +/- 0.05 at 355 nm and Φ + 0.62 +/- 0.05 at 532 nm.The effects of the central metal on photodenitrosylation are described.The laser photolysis of NOFeTPP in the presence of low concentration of pyridine revealed that the FeIITPP initially produced reacts with a pyridine molecule, Py, to form five-coordinate (Py)FeIITPP.The five-coordinate (Py)Fe%II%TPP further reacts with Py to give six-coordinate (Py)2FeIITPP, which recombines with NO to regenerate NOFeTPP.The kinetic study has demonstrated that the five-coordinate (Py)FeIITPP which is in equilibrium with (Py)2FeIITPP is responsible for the recombination reaction of (Py)2FeIITPP and NO.
- Hoshino, Mikio,Kogure, Mieko
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p. 5478 - 5484
(2007/10/02)
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- Dioxygen Insertion into Iron(III)-Carbon Bonds. NMR Studies of the Formation and Reactivity of Alkylperoxo Complexes of Iron(III) Porphyrins
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The behavior of PFeIIICHR2 (P is a porphyrin dianion) in solution especially in the presence of dioxygen has been examined by (1)H and (2)H NMR measurements.Evidence for the photolytic Fe-C bond homolysis with the formation of PFeII is presented.Addition of dioxygen to PFeCH2R produces two unstable intermediates, PFeIIIO2CH2R and PFeIIIOH, which may be directly observed at low temperatures.These form and decompose through the following reactions: PFeIIICH2R + O2 -> PFeIIIO2CHR2; PFeIIIO2CHR2 -> PFeIIIOH + O=CR2; 2PFeIIIOH -> PFeIIIOFeIIIP + H2O.The formation of the product aldehyde or ketone has been established for methyl, ethyl, isopropyl, n-propyl, and benzyl ligands axially coordinating iron.The dioxygen insertion is retarded by the coordination of N-methylimidazole to the sixth iron coordination site or by employing a sterically encumbered porphyrin.PFeIIIOH catalyzes the decomposition of ethyl hydroperoxide to give acetaldehyde as the major organic product.
- Arasasingham, Ramesh D.,Balch, Alan L.,Cornman, Charles R.,Latos-Grazynski, Lechoslaw
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p. 4357 - 4363
(2007/10/02)
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- Synthesis of 5,10,15,20-tetrakisphenylporphins on a carbon support for the cathodic reduction of oxygen in fuel cells
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Several substituted Fe- and Co-containing tetraphenylporphins I were loaded on carbon either by adsorption from acetone or by in situ synthesis on the carbon support. The porphin/carbon combinations were pyrolyzed at 800°C. The electrocatalytic activities in the reduction of dioxygen were investigated in alkaline (KOH) and acid (H2SO4) solutions using porous Teflon-bonded carbon electrodes impregnated with the catalysts. At 700 mV high current densities of 75 mA/cm2 in acid solution and up to 90 mA/cm2 in alkaline solution were obtained.
- Kirschenmann,Woehrle
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p. 1403 - 1406
(2007/10/02)
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- Picosecond Absorption Studies on the Excited State of (μ-Oxo)bis
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We have measured the kinetics and spectra of the intermediates of (μ-oxo)bis in various solvents.The spectra of the intermediate species were measured at various intervals of time from -100 to 4.3 ns after excitation with a 532- or 355-nm 25-ps pulse.The intermediate state, possibly a cation radical, was assigned to a monomer that forms the photodissociated pair TPPFeII+ + TPPFeIII-O- and yields a small amount of disproportionation reaction products, FeIITPP and TPPFeIV=O.t
- Guest, C. R.,Straub, K. D.,Hutchinson, J. A.,Rentzepis, P. M.
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p. 5276 - 5280
(2007/10/02)
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- Biomimetic oxidation with molecular oxygen. Selective carbon-carbon bond cleavage of 1,2-diols by molecular oxygen and dihydropyridine in the presence of iron-porphyrin catalysts
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The selective carbon-carbon bond cleavage of 1,2-diols in the presence of an iron-porphyrin complex, molecular oxygen, and 1-benzyl-3-carbamoyl-1,4-dihydropyridine is reported. The C-C bonds of aryl-substituted ethane-1,2-diols were cleaved exclusively to aldehydes or ketones as the oxidation products at room temperature. The reaction rates were influenced by the steric hindrance of the substituents both in the catalysts and diols, but no differences in the reactivities were observed between the two stereo isomers (meso and dl) of diols. A kinetic analysis of this bond cleavage reaction is consistent with the reaction mechanism consisting of the initial binding of diol on the active catalyst forming an intermediate complex and its subsequent breakdown in the rate-determining step of the catalytic cycle. The initial binding step is favorable for electron-deficient diols and is influenced by steric hindrance, whereas the rate-determining bond cleavage step is accelerated by electron-rich diols and unaffected by the steric effect. The mechanism of this diol cleavage reaction is discussed on the basis of these observations. The selective carbon-carbon bond cleavage of 1,2-diols in the presence of an iron-porphyrin complex, molecular oxygen, and 1-benzyl-3-carbamoyl-1,4-dihydropyridine is reported. The C-C bonds of aryl-substituted ethane-1,2-diols were cleaved exclusively to aldehydes or ketones as the oxidation products at room temperature. The reaction rates were influenced by the steric hindrance of the substituents both in the catalysts and diols, but no differences in the reactivities were observed between the two stereo isomers (meso and dl) of diols. A kinetic analysis of this bond cleavage reaction is consistent with the reaction mechanism consisting of the initial binding of diol on the active catalyst forming an intermediate complex and its subsequent breakdown in the rate-determining step of the catalytic cycle.
- Okamoto,Sasaki,Oka
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p. 1187 - 1196
(2007/10/02)
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- Comparison of Variable-Temperature 1H NMR Spectra of Five-Coordinate High-Spin (S=5/2) Iron(III) Porphyrins and Chlorins
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Variable-temperature 1H NMR spectra are reported for five different five-coordinate high-spin (S=5/2) iron(III) chlorin complexes.The complexes are Fe(TPC)X (X-=Cl-, OTeF5-) and Fe(OEC)X (X-=Cl-, OTeF5-, NCS-), where TPC=tetraphenylchlorinate dianion and OEC=octaethylchlorinate dianion.For completeness, variable-temperature spectra are also reported for the five homologous porphyrin complexes, although with one exception, Fe(OEP)(NCS), these porphyrin data have been reported by others.Spectra and Curie plots for the two classes of complexes are compared and spectral characteristics that are unique to chlorins are discussed.Our data show that the various types of pyrrole protons in the TPCcomplexes and the various types of pyrrole methylene protons in the OEC complexes exhibit a large range of isotropic shifts, ca. 30 ppm at ca. 300 K.The average temperature dependence of the resonances (i.e., Curie plot slopes) is similar to the temperature dependence of the resonance(s) for porphyrin protons in chemically similar positions.For both sets of chlorin complexes, pyrroline proton or methylene proton isotropic shifts are substantially smaller than pyrrole isotropic shifts, while pyrroline proton or methylene proton line widths are larger than pyrrole proton line widths.Large deviations in Curie plot 1/T=0 intercepts from diamagnetic chemical shifts are observed for many of the chlorin proton resonances.This behavior has been observed for all paramagnetic iron(II,III) hydroporphyrins studied to date.The different axial ligands greatly influence the range of isotropic shifts for the pyrrole protons or pyrrole methylene protons for a given chlorin and the temperature dependence (Curie plot slopes and intercepts) of the pyrroline protons for the TPC complexes.
- Pawlik, M. J.,Miller, P. K.,Sullivan, E. P.,Levstik, M. A.,Almond, D. A.,Strauss, S. H.
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p. 3007 - 3012
(2007/10/02)
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- PHOTOREDUCTION OF MANGANESE(III), IRON(III), COBALT(III), AND MOLYBDENUM(V) TETRAPHENYLPORPHYRINS IN 2-METHYLTETRAHYDROFURAN
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The central metals in the metallotetraphenylporphyrins with axial halo or pseudohalo ligands, MnIII(tpp)X (tpp = 5,10,15,20-tetraphenylporphinato; X = I, Br, Cl, OAc, NCS), FeIII(tpp)Cl, CoIII(tpp)Cl, and MoVO(t
- Imamura, Taira,Jin, Takashi,Suzuki, Toru,Fujimoto, Masatoshi
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p. 847 - 850
(2007/10/02)
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