Fe TPP Research Articles

Investigation of Iron(III) Tetraphenylporphyrin as a Redox Flow Battery Anolyte: Unexpected Side Reactivity with the Electrolyte.

Redox flow batteries (RFBs) present an opportunity to bridge the gap between the intermittent availability of green energy sources and the need for on-demand grid level energy storage. While aqueous vanadium-based redox flow batteries have been commercialized, they are limited by the constraints of using water as an electrochemical solvent. Nonaqueous redox flow battery systems can be used to produce high voltage batteries due to the larger electrochemical window in nonaqueous solvents and the ability to tune the redox properties of active materials through functionalization. Iron porphyrins, a class of organometallic macrocycles, have been the subject of many studies for their photocatalytic and electrocatalytic properties in nonaqueous solvents. Often, iron porphyrins can undergo multiple redox events making them interesting candidates for use as anolytes in asymmetrical redox flow batteries or as both catholyte and anolyte in symmetrical redox flow battery systems. Here the electrochemical properties of Fe(III)TPP species relevant to redox flow battery electrolytes are investigated including solubility, electrochemical properties, and charge/discharge cycling. Commonly used support electrolyte salts can have reactivities that are often overlooked beyond their conductivity properties in nonaqueous solvents. Parasitic reactions with the cations of common support electrolytes are highlighted herein, which underscore the careful balance required to fully assess the potential of novel RFB electrolytes.

Stability of Fe(III) and Sn(IV) Metalloporphyrins Adsorbed on Cation-Exchanged Montmorillonite

The iron(III)tetraphenylporphyrin chloride Fe(III)TPPCl, iron(III)tetra-naphthylporphyrin Fe(III)TNPCl, μ-oxo-bis[tetraphenylporphyriniron(III)] [(Fe(III)TPP)2O], μ-oxo-bis[tetranaphthylporphyriniron(III)] [(Fe(III)TNP)2O], tin(IV)tetraphenylporphyrin chloride Sn(IV)TPPCl2 and tin(IV)tetra-naphthylporphyrin Sn(IV)TNPCl2 complexes were all found to be adsorbed onto the montmorillonite MMT clay without demetallation. The evidence from the visible absorption and diffuse reflectance spectra all showed that the species present on the montmorillonite are the metallated form. Also the evidence from Mossbauer spectroscopy confirm these findings. The only process that occurs is that the dimeric form of the iron complexes underwent transformation to the monomeric form. The clay-complex systems were characterized using visible absorption spectra, diffuse reflectance spectra, X-ray diffraction, Mossbauer spectra and Electron microscopy.
 HIGHLIGHTS
 
 Fe(III)TPPCl, Fe(III)TNPCl, Sn(IV)TPPCl2, and Sn(IV)TNPCl2 porphyrin complexes adsorbed onto the montmorillonite clay without demetallation
 The dimeric forms of iron porphyrin complexes [(Fe(III)TPP)2O] and [(Fe(III)TNP)2O are converted to the monomeric form when adsorbed on montmorillonite clay
 The weak acidity of montmorillonite clay does not have the ability to cause demetallation of the metallo complexes of porphyrin

Immobilisation of Iron Porphyrin from an Equilibrium Solution with Diazonium‐Functionalised Axial Ligand: Dependence of Film Composition on Grafting Potential

AbstractIn dichloromethane solution, tetraphenylporphyrin iron (III) chloride (FeTPPCl) and 4‐(1H‐Imidazol‐1‐yl)aniline (Im‐Ph‐NH2) exist in equilibrium with axially‐coordinated [FeTPP(Im‐Ph‐NH2)n]+ (n=1 and 2). After in situ diazotisation of Im‐Ph‐NH2, electroreduction of the diazonium ion leads to deposition of a film incorporating [FeTPP(Im‐Ph)2]+ and uncoordinated Im‐Ph. In the 1 : 1 FeTPPCl:Im‐Ph‐NH2 grafting solution used in this work, Im‐Ph‐NH2 is mostly uncoordinated. However, the formation constant for axially coordinated Fe(II)TPP is significantly greater than for Fe(III)TPP+. Consequently, the relative amounts of coordinated and uncoordinated Im‐Ph in the films depends on whether the grafting scans traverse the potential for reduction of FeTPPCl. In addition, redox grafting can occur based on the Fe(III)/(II) couple of solution‐ and film‐based porphyrin. Electrochemistry, atomic force microscopy and X‐ray photoelectron spectroscopy reveal that the relative amount of free and coordinated Im‐Ph, and concentration of [FeTPP(Im‐Ph)2]+ in the films depend on the negative potential limit during grafting.

Tertiary Amine-Assisted Electroreduction of Carbon Dioxide to Formate Catalyzed by Iron Tetraphenylporphyrin

The reduction of CO2 by electrogenerated Fe(0)TPP can be directed toward formate with a good selectivity (ca. 70%) upon addition of a tertiary amine in the presence of a weak proton donor. Whereas most systems generating formate from CO2 involve the initial formation of a hydride, we demonstrate herein that the hydride pathway is avoided by preferential binding of CO2 that may then be protonated by weak acids. The net result is that hydrogen production via the hydride is disfavored, thus leading to high yields of formate. These results demonstrate an alternative route for the activation of CO2 to formate.

Comparative FTIR study of the cobalt and iron porphyrin reactions with CO. Does cobalt porphyrin form a bis-carbonyl complex in the Ar matrix?

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 may form mono-carbonyl adducts with CO, however formation of bis-carbonyl adduct was confirmed only for iron porphyrin. These results refute an earlier assumption regarding existence of Co(TPP)(CO)2 in Ar matrix.

High Performance Fe Porphyrin/Ionic Liquid Co-catalyst for Electrochemical CO2 Reduction.

The efficient and selective catalytic reduction of CO2 is a highly promising process for both of the storage of renewable energy as well as the production of valuable chemical feedstocks. In this work, we show that the addition of an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, in an aprotic electrolyte containing a proton source and FeTPP, promotes the in situ formation of the [Fe(0) TPP](2-) homogeneous catalyst at a less negative potential, resulting in lower overpotentials for the CO2 reduction (670 mV) and increased kinetics of electron transfer. This co-catalysis exhibits high Faradaic efficiency for CO production (93 %) and turnover number (2 740 000 after 4 hour electrolysis), with a four-fold increase in turnover frequency (TOF) when compared with the standard system without the ionic liquid.

Electronic effects of the substituent on the dioxygen-activating abilities of substituted iron tetraphenylporphyrins: a theoretical study.

A density functional theoretical (DFT) method was applied to understand the effects of the substituent on dioxygen activation by a series of substituted iron tetraphenylporphyrins [FeT(o/p-R)PP (o = ortho-substituted, p = para-substituted; R = -H, -Cl, -NO2, -CH3, -OCH3)]. The ground states (GS) of the dioxygen adducts of the substituted iron tetraphenylporphyrins [FeT(o/p-R)PPO2] were determined at the B3LYP/6-31G(d) level without any symmetry constraints. Binding energy calculations indicated that the presence of electron-withdrawing substituents at the para position favors O2 binding. Calculations of the O-O bond length of the adsorbed dioxygen revealed that the influence of the p-substituent on the activation of dioxygen decreases in the order p-CH3 > p-Cl > p-OCH3 > -H > p-NO2, while the influence of the o-substituent decreases in the order o-NO2 > o-CH3 > o-Cl > o-OCH3 > -H. The low-lying excited states (LLES) of the FeT(o/p-R)PPO2 adducts suggest that the ability to activate dioxygen decreases in the order o-CH3 > o-OCH3 = -H > o-NO2 > o-Cl for o-substituents and p-CH3 > p-Cl > -H > p-NO2 > p-OCH3 for p-substituents. NBO charge population analysis and spin density analysis showed that substitution caused more β-electrons to be transferred from the iron tetraphenylporphyrin to the dioxygen, which enhanced dioxygen activation. Spin density analysis confirmed that the β-electron population at the adsorbed dioxygen is an accurate indicator of the degree of dioxygen activation. The trend observed in porphyrin catalytic activity as the substituent on the dioxygen adduct was varied is consistent with the trend in the binding energy. It is clear that substituents at the ortho and para positions in these dioxygen adducts play different roles in dioxygen activation.

Impact of iron limitation on primary production (dissolved and particulate) and secondary production in cultured Trichodesmium sp.

Diazotrophic cyanobacteria play an important role in biogeochemical cycles of carbon and nitrogen and, hence, in oceanic productivity in the tropical and subtropical regions of the ocean. Although many studies have examined the impact of iron (Fe) limitation on particulate primary production and dinitrogen (N2) fixation in the colonial cyanobacterium Trichodesmium, none have looked at the impact of Fe limitation on the percentage extracellular release (PER) and secondary production (SP) in Fe-limited cultures of this cyanobacterium. Here, we present the results of a series of culture experiments during which we examined the impact of 3 concentrations of dissolved iron (DFe) on total primary production (TPP = dissolved + particulate primary production, i.e. DPP + PPP), PER and on SP. Under severe Fe limitation (5 nM DFe), biomass, growth rates, TPP and N2 fixation were strongly reduced, while PER increased relative to the rates ob served at the highest Fe concentration. Moreover, reducing Fe concentration induced an increase in the percentage of photosynthetically fixed C used for algal growth, while the percentage of C used to support algal respiration decreased. Reduced Fe concentrations also induced a decrease in SP and in the SP:DPP ratio, indicating that the efficiency of transfer of fixed carbon from autotrophic to heterotrophic processes is reduced. This suggests that Fe, either directly through influencing cellular processes or indirectly through influencing organic matter structure or nitrogen availability, is controlling SP and, thus, microbial carbon utilization. These results suggest that the amount of carbon entering into the microbial loop may be reduced under Fe limitation, thus leading to an accumulation of dissolved organic carbon with potentially important impacts on microbial carbon cycling and, ultimately, on the biological carbon pump

Substituent effects on geometric and electronic properties of iron tetraphenylporphyrin: a DFT investigation

To investigate the effects of the substituents, substituent positions and axial chloride ligand on the geometric and electronic properties of the iron tetraphenylporphyrin (FeTPP), a series of the substituented iron tetraphenylporphyrins and their chlorides, FeT(o/p-R)PP and FeT(o/p-R)PPCl (R = -H, -Cl, -NO(2), -OH, -OCH(3)), were systematically calculated without any symmetry constraint by using DFT method. For geometric structure, the substituent position and axial Cl ligand change the configuration of the iron porphyrin obviously. The ortho-substituents prefer making the phenyls perpendicular to the porphyrin ring; the axial chloride draws the central Fe ion ~0.500 Å out of the porphyrin plane toward the ligand. With regard to electronic properties, it is found that E(LUMO) could be related to the catalytic activity. The electron-withdrawing group always lowers the energies of both frontier orbitals, while the electron-donating one heightens them simultaneously, but they affect the E(HOMO) and E(LUMO) in the same sequence, -NO(2) < -Cl < -H < -OH < -OCH(3). The substituent effects on the central Fe ion were explored by calculating NBO charge distribution, spin density and natural electron configuration.

Comparison of the Reactivity of Antimalarial 1,2,4,5-Tetraoxanes with 1,2,4-Trioxolanes in the Presence of Ferrous Iron Salts, Heme, and Ferrous Iron Salts/Phosphatidylcholine

Dispiro-1,2,4,5-tetraoxanes and 1,2,4-trioxolanes represent attractive classes of synthetic antimalarial peroxides due to their structural simplicity, good stability, and impressive antimalarial activity. We investigated the reactivity of a series of potent amide functionalized tetraoxanes with Fe(II)gluconate, FeSO(4), FeSO(4)/TEMPO, FeSO(4)/phosphatidylcholine, and heme to gain knowledge of their potential mechanism of bioactivation and to compare the results with the corresponding 1,2,4-trioxolanes. Spin-trapping experiments demonstrate that Fe(II)-mediated peroxide activation of tetraoxanes produces primary and secondary C-radical intermediates. Reaction of tetraoxanes and trioxolanes with phosphatidylcholine, a predominant unsaturated lipid present in the parasite digestive vacuole membrane, under Fenton reaction conditions showed that both endoperoxides share a common reactivity in terms of phospholipid oxidation that differs with that of artemisinin. Significantly, when tetraoxanes undergo bioactivation in the presence of heme, only the secondary C-centered radical is observed, which smoothly produces regioisomeric drug derived-heme adducts. The ability of these tetraoxanes to alkylate the porphyrin ring was also confirmed with Fe(II)TPP and Mn(II)TPP, and docking studies were performed to rationalize the regioselectivity observed in the alkylation process. The efficient process of heme alkylation and extensive lipid peroxidation observed here may play a role in the mechanism of action of these two important classes of synthetic endoperoxide antimalarial.

Investigation of hydrogen depletion of organic materials upon ion beam irradiation by simultaneous micro-RBS and micro-ERDA techniques

abstract Radiation stability investigations in a form of hydrogen depletion of organic materials induced by afocussed 1.6 MeV He + scanning ion beam within a beam intensity range of 10–50 pA/ l m 2 is reported.The hydrogen depletion was measured by applying Elastic Recoil Detection Analysis (ERDA) and Ruther-ford Backscattering Spectrometry (RBS) techniques, simultaneously. H-count rates were measured andfurther processed as a function of the deposited ion beam fluence. Our results show, that within thedeposited fluence range of 10 14 –10 15 ions/cm 2 both the Kapton-foil and porphyrin complex (Fe(III)TPP)do not suffer from hydrogen depletion process, indicating only minor chemical structural changes. Thereis a slight decrease of the hydrogen content of the Mylar-foil while a remarkable loss of hydrogen occursin case of poly(dimethyl-siloxane) (PDMS) suggesting the degradation of the polymer chain. A fulldescription of our versatile and complex particle detection system for nuclear microprobe applicationsis also given in the paper. 2010 Elsevier B.V. All rights reserved.

Fe(F20TPP)Cl] catalyzed intramolecular C–N bond formation for alkaloid synthesis using aryl azides as nitrogen source

The syntheses of alkaloids including indoles, indolines, tetrahydroquinolines, dihydroquinazolinones and quinazolinones have been accomplished in moderate to excellent yields via [Fe(F(20)TPP)Cl] catalyzed intramolecular C-N bond formation using aryl azides as nitrogen source.

Spectral study of the dioxygen and carbonyl adducts of ferrous porphyrins ligated by neutral S-donors

A series of the six-coordinated ferrous porphyrin complexes (L)Fe(II)TPP(O 2) and (L)Fe(II)TPP(CO) (L, (CH 3) 2S, or C 2H 5SH, TPP, meso-tetraphenylporphyrin dianion) was prepared. UV–vis and FTIR spectroscopy were applied to follow the reaction of O 2 and CO adducts of Fe(II) porphyrins with neutral thiol and thioether. Using sublimed layers methodology and low temperature technique, as well as isotope substitution, the formation of six-coordinate complexes was monitored in situ. The comparison of CO and O 2 stretching frequencies of thiol and thioether adducts indicates that the degree of electron donation is similar for these ligands. The complexes of Me 2S and EtSH with Fe(TPP)(O 2) are stable at 150 K and slowly decompose at elevated temperatures. In contrast, the carbonyl complexes of Fe(Por) with Me 2S and EtSH are relatively stable and retain six-coordination at room temperature. The electronic effects of axial S-donor ligands on the coordinated O 2 and CO are discussed and compared with the effects of N- and O-donors.

X-ray Absorption Spectroscopy of Hemes and Hemeproteins in Solution: Multiple Scattering Analysis

A full quantitative analysis of Fe K-edge X-ray absorption spectra has been performed for hemes in two porphynato complexes, that is, iron(III) tetraphenylporphyrin chloride (Fe(III)TPPCl) and iron(III) tetraphenylporphyrin bis(imidazole) (Fe(III)TPP(Imid)2), in two protein complexes whose X-ray structure is known at atomic resolution (1.0 A), that is, ferrous deoxy-myoglobin (Fe(II)Mb) and ferric aquo-myoglobin (Fe(III)MbH2O), and in ferric cyano-myoglobin (Fe(III)MbCN), whose X-ray structure is known at lower resolution (1.4 A). The analysis has been performed via the multiple scattering approach, starting from a muffin tin approximation of the molecular potential. The Fe-heme structure has been obtained by analyzing independently the Extended X-ray Absorption Fine Structure (EXAFS) region and the X-ray Absorption Near Edge Structure (XANES) region. The EXAFS structural results are in full agreement with the crystallographic values of the models, with an accuracy of +/- 0.02 A for Fe-ligand distances, and +/-6 degrees for angular parameters. All the XANES features above the theoretical zero energy (in the lower rising edge) are well accounted for by single-channel calculations, for both Fe(II) and Fe(III) hemes, and the Fe-N p distance is determined with the same accuracy as EXAFS. XANES evaluations of Fe-5th and Fe-6th ligand distances are determined with 0.04-0.07 A accuracy; a small discrepancy with EXAFS (0.01 to 0.05 A beyond the statistical error), is found for protein compounds. Concerns from statistical correlation among parameters and multiple minima in the parameter space are discussed. As expected, the XANES accuracy is slightly lower than what was found for polarized XANES on Fe(III)MbCN single crystal (0.03-0.04 A), and states the actual state-of-the-art of XANES analysis when used to extract heme-normal parameters in a solution spectrum dominated by heme-plane scattering.

Highly selective oxidation of toluene using air over [Fe(III)TPP]Cl supported on chitosan

The highly selective catalytic oxidation of toluene with air to benzaldehyde and benzyl alcohol in the liquid phase has been studied with the use of iron tetraphenylporphyrin (Fe TPP) supported on chitosan (CTS), (Fe TPP/CTS). The rates of toluene conversion and selectivity (aldehyde + alcohol) were subject to the reaction temperature, air pressure, and amount of iron tetraphenylporphyrin. By the use of the Fe TPP/CTS, containing 2 mg of iron tetraphenylporphyrin as catalyst, toluene oxidation with air under the optimum conditions of 190 °C and 0.6 MPa produced benzaldehyde and benzyl alcohol at 90% selectivity and 5.4% conversion of toluene, the mole turnover of the catalyst was about 6 × 106, and it could be reused efficiently for one more time. It is suggested that the amine groups (–NH2) on the chitosan chain act as a key assistor to the catalysis of Fe TPP for toluene oxidation. Compared with the conventional method of synthesizing benzaldehyde and benzyl alcohol, the new method has the advantages of reduced environmental pollution, higher selectivity for the two main products, and easy recovery of the catalyst.Key words: chitosan-supported iron porphyrin, catalysis, toluene oxidation, benzaldehyde, benzyl alcohol.

Nitrogen Ligand Complexes of Metal Chlorides as Effective Catalysts for the Highly Regio- and Chemoselective Silylation of Hydroxyl Groups with Hexamethyldisilazane (HMDS) at Room Temperature

Zn(bipy)3Cl2, Fe(bipy)Cl3, and Fe(tpp)Cl are effective catalysts for silylation of hydroxy groups with HMDS at room temperature in dry CH3CN. High selectivity is observed between primary and secondary hydroxy functional groups. This method absolutely discriminates other functional groups containing labile hydrogen atoms.

Mechanisms for the formation of six-coordinate Fe(III)TPP-peroxide complexes studied by simultaneous ESR and optical measurements

ESR and optical absorption measurements were performed for six-coordinate Fe(III)TPP-butyl peroxide complexes formed in the reaction system composed of Fe(III)TPPCl, NaOCH 3 and t- or n-butyl hydroperoxide. The presence of four paramagnetic iron complexes was detected in the reaction system. Based on the spectroscopic parameters, the spin state and the axial ligand of these species were deduced as follows: Fe(III)TPP-(HOCH 3)( −OCH 3) ( A), -( −OCH 3) 2 ( B), ( −OCH 3)( −OO-butyl) ( C), -( −OO-butyl) 2 ( D) coordination reactions of t- and n-butyl hydroperoxide and complexes A and B were monitored on changing the molar ratio of [t- or n-butylperoxide]/ [Fe(III)TPPCl]. The observed spectral changes justified that complexes A and B were successively changed to complex D through complex C. The concentration of these four paramagnetic complexes was estimated by means of the duplicate integration of the observed ESR spectra at 4.2 K. The molar distribution of complexes A, B, C and D was simulated by taking into account the formation constants relating to the generation of the peroxide complexes C and D. By comparison of the formation constants, the possible mechanisms for Fe(III)TPP-peroxide complex formation were discussed.

π-Cation radicals of iron(III) derivatives of deformed porphyrins

π-Cation radicals of iron(III) derivatives of some deformed porphyrins have been characterised using UV/VIS, IR and 1H NMR spectroscopy and by magnetic susceptibility measurements. The deformation in these systems has been induced by a covalent attachment of short bridging chains across the porphyrin periphery. Molecular mechanics simulation clearly reveals the enforced deformation in the porphyrin cores of the free bases inferred from the multiplet structure for the pyrrole protons by 1H NMR spectroscopy. Significant red shifts in Soret (171–340 cm–1) and Q-band (76–354 cm–1) absorption maxima for the iron(III) derivatives relative to [Fe(tpp)Cl](H2tpp = 5,10,15,20-tetraphenylporphyrin) implies the retention of deformation in solution. Collective evidence from IR, UV/VIS and 1H NMR spectroscopy and magnetic susceptibility measurements suggests for the oxidised derivatives a high-spin iron(III) state (S=5//2) antiferromagnetically coupled to a porphyrin radical cation (S=1//2). Magnetic moment values (4.8–5.1 µβ) measured for solids and CD2Cl2 solutions indicate an intramolecular d–π coupling facilitated through an antiferromagnetic exchange. These results substantiate the emerging correlation between the structure of the macrocycle and the metal–ligand magnetic interactions in high-spin iron(III) porphyrin radical-cation complexes.

Cytochrome P450-Butyl Peroxide Complex Detected by ESR

ESR measurements were performed for the reaction systems composed of t- or n-butylhydroperoxide and cytochrome P-450 (UT-2), purified from rat liver microsomes. On addition of n-butylhydroperoxide to the P-450 at pH 7.4, ESR signal due to a ferric low-spin species (g1=2.29, g2=2.24 and g3=1.96) was recorded. The observed g-parameters agreed well with those of a model thiolate-heme-iron(III)-peroxide complex, Fe(III)TPP(−S-TGE)(−OO-t-butyl) (g1=2.285, g2=2.198 and g3=l.959). In terms of the g-parameters, the new P-450 complex was concluded to be a F450-butyl peroxide adduct, in which a butyl peroxide anion ligates at the sixth position of heme iron(III).

Dalton communications. Models of cytochromes b containing an organometallic axial base, azaferrocene: synthesis and electron paramagnetic resonance study

Azaferrocene reacted with [Fe(oep)(O3SCF3)] or [Fe(tpp)(O3SCF3)](oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate; tpp = 5,10,15,20-tetraphenylporphyrinate to afford [Fe(oep){Fe(C5H5)(C4H4N}2]O3SCF3 or [Fe(tpp){Fe(C5H5)(C4H4N)}2]O3SCF3, respectively; the trinuclear complexes exhibit rhombic low-spin EPR spectra indicating the strong ligating ability of azaferrocene.