77439-20-4Relevant academic research and scientific papers
Effect of the axial ligand on the reactivity of the oxoiron(IV) porphyrin π-cation radical complex: Higher stabilization of the product state relative to the reactant state
Takahashi, Akihiro,Yamaki, Daisuke,Ikemura, Kenichiro,Kurahashi, Takuya,Ogura, Takashi,Hada, Masahiko,Fujii, Hiroshi
, p. 7296 - 7305 (2012/07/28)
The proximal heme axial ligand plays an important role in tuning the reactivity of oxoiron(IV) porphyrin π-cation radical species (compound I) in enzymatic and catalytic oxygenation reactions. To reveal the essence of the axial ligand effect on the reactivity, we investigated it from a thermodynamic viewpoint. Compound I model complexes, (TMP+a?€￠) FeIVO(L) (where TMP is 5,10,15,20-tetramesitylporphyrin and TMP +? is its π-cation radical), can be provided with altered reactivity by changing the identity of the axial ligand, but the reactivity is not correlated with spectroscopic data (ν(Fe=O), redox potential, and so on) of (TMP+?)FeIVO(L). Surprisingly, a clear correlation was found between the reactivity of (TMP+?)FeIVO(L) and the FeII/FeIII redox potential of (TMP)Fe IIIL, the final reaction product. This suggests that the thermodynamic stability of (TMP)FeIIIL is involved in the mechanism of the axial ligand effect. Axial ligand-exchange experiments and theoretical calculations demonstrate a linear free-energy relationship, in which the axial ligand modulates the reaction free energy by changing the thermodynamic stability of (TMP)FeIII(L) to a greater extent than (TMP +?)FeIVO(L). The linear free energy relationship could be found for a wide range of anionic axial ligands and for various types of reactions, such as epoxidation, demethylation, and hydrogen abstraction reactions. The essence of the axial ligand effect is neither the electron donor ability of the axial ligand nor the electron affinity of compound I, but the binding ability of the axial ligand (the stabilization by the axial ligand). An axial ligand that binds more strongly makes (TMP)FeIII(L) more stable and (TMP+?)FeIVO(L) more reactive. All results indicate that the axial ligand controls the reactivity of compound I (the stability of the transition state) by the stability of the ground state of the final reaction product and not by compound I itself.
Redox potentials of oxoiron(IV) porphyrin π-cation radical complexes: Participation of electron transfer process in oxygenation reactions
Takahashi, Akihiro,Kurahashi, Takuya,Fujii, Hiroshi
experimental part, p. 6922 - 6928 (2011/09/20)
The oxoiron(IV) porphyrin π-cation radical complex (compound I) has been identified as the key reactive intermediate of several heme enzymes and synthetic heme complexes. The redox properties of this reactive species are not yet well understood. Here, we report the results of a systematic study of the electrochemistry of oxoiron(IV) porphyrin π-cation radical complexes with various porphyrin structures and axial ligands in organic solvents at low temperatures. The cyclic voltammogram of (TMP)FeIVO, (TMP = 5,10,15,20-tetramesitylporphyrinate), exhibits two quasi-reversible redox waves at E1/2 = 0.88 and 1.18 V vs SCE in dichloromethane at -60 °C. Absorption spectral measurements for electrochemical oxidation at controlled potential clearly indicated that the first redox wave results from the (TMP)FeIVO/[(TMP+?)FeIVO]+ couple. The redox potential for the (TMP)FeIVO/[(TMP +?)FeIVO]+ couple undergoes a positive shift upon coordination of an anionic axial ligand but a negative shift upon coordination of a neutral axial ligand (imidazole). The negative shifts of the redox potential for the imidazole complexes are contrary to their high oxygenation activity. On the other hand, the electron-withdrawing effect of the meso-substituent shifts the redox potential in a positive direction. Comparison of the measured redox potentials and reaction rate constants for epoxidation of cyclooctene and demethylation of N,N-dimethylanilines enable us to discuss the details of the electron transfer process from substrates to the oxoiron(IV) porphyrin π-cation radical complex in the oxygenation mechanisms.
Effect of imidazole and phenolate axial ligands on the electronic structure and reactivity of oxoiron(IV) porphyrin π-cation radical complexes: Drastic increase in oxo-transfer and hydrogen abstraction reactivities
Takahashi, Akihiro,Kurahashi, Takuya,Fujii, Hiroshi
, p. 2614 - 2625 (2009/07/30)
To study the effect of axial ligands on the electronic structure and reactivity of compound I of peroxidases and catalases, oxoiron(IV) porphyrin π-cation radical complexes with imidazole, 2-methylimidazole, 4(5)-methylimidazole, and 3-fluoro-4-nitropheno
Models of nitric oxide synthase: Iron(III) porphyrin-catalyzed oxidation of fluorenone oxime to nitric oxide and fluorenone
Wang, Charles C.-Y.,Ho, Douglas M.,Groves, John T.
, p. 12094 - 12103 (2008/10/08)
Nitric oxide synthase (NOS) is a heme-containing monoxygenase that catalyzes the oxidation of L-arginine to L-citrulline and NO in two steps. In the second step of the NOS reaction, citrulline and NO are generated from the heme-catalyzed 3-electron oxidation of L-N-hydroxyarginine. To model this unusual reaction, iron porphyrin-catalyzed oxygenations of oximes with O2 were investigated. The oxidation of fluorenone oxime and a stoichiometric amount of hydroxoiron(III) porphyrin (Fe(OH)P, P = TMP and TPFPP) with O2 in benzene generated Fe(NO)P, fluorenone, and O-(9-nitro-9-fluorenyl)fluorenone oxime. The X-ray crystal structure of the oxime ether product suggests that it originated from the dimerization of the fluorenyl iminoxy radicals. Detailed analysis of this reaction showed that the oxime reacted first with Fe(OH)P to generate a 5-coordinate, high-spin oximatoiron(III) porphyrin species [Fe(oximate)P]. The X-ray crystal structure of oximatoiron(III) tetrakis(2,6-dichlorophenyl)porphyrin [Fe(oximate)TDCPP] showed that the oximate ligand was monodentate, O-bound to Fe(III)P. The aerobic oxidation of Fe(oximate)P followed the characteristic kinetics of a metalloporphyrin- catalyzed radical-type autoxidation. O2 surrogates, the π-acids NO and CO, induced the homolysis of Fe(oximate)P to generate Fe(NO)P or Fe(CO)P and the iminoxy radical, implicating a similar reaction mode for O2 with Fe(oximate)P. Fe(oximate)TMP reacted with 18O2 to generate predominantly 18O-labeled fluorenone (75% yield), while the reaction conducted under 16O2 and H218O generated only 16O-labeled fluorenone. This reaction is proposed to proceed via an Fe-O bond homolysis of Fe(oximate)TMP followed by O2 insertion to generate 9-nitroso-9-fluorenylperoxyFe(III)TMP, which decomposes via an O-O bond homolysis to generate NO, fluorenone, and oxoFe(IV)P. The implications of this system for the NOS reaction mechanism are discussed.
Reactions of aryl-iron(III) porphyrins with dioxygen. Formation of aryloxy-iron(III) and aryl-iron(IV) complexes
Arasasingham, Ramesh D.,Balch, Alan L.,Hart, Rebecca L.,Latos-Grazyński, Lechos?aw
, p. 7566 - 7571 (2007/10/02)
The reaction of dioxygen with low-spin, five-coordinate complexes, PFeIIIAr (P, porphyrin dianion; Ar, aryl group) has been examined for comparison with previous work (Arasasingham, R. D. et al. J. Am. Chem. Soc. 1989, 111, 4357) on the corresponding alkyl complexes which showed that peroxo complexes PFeIIIOOR formed initially and then decomposed to form PFeOH and an aldehyde or ketone when R was a primary or secondary alkyl group. Dioxygen addition to TTPFeIII(C6H4CH3-ρ) at 25 °C in toluene yields the phenoxide complex, TTPFe(OC6H4CH3-ρ), as the principle product, while addition to TTPFeIIIC6H5 at -30 °C yields TTPFeIIIOC6H5 and small amounts of TTPFeIII(OC6H4OH-ρ) and TTPFeIIIOC6H4OFeIIITTP. These reactions have been monitored by both 1H NMR and ESR spectroscopies. No intermediates have been detected in the formation of these products. Mechanisms for the formation of these products have been formulated in terms of the initial insertion of dioxygen into the Fe-C bond followed by rapid homolysis to form PFeIV=O and .OAr, with subsequent reactions yielding the final products. Addition of dioxygen to a solution of TTPFeIII(C6H4CH3-ρ) in chloroform at -60 °C yields a mixture of [TTPFeIV(C6H4CH3-ρ)]+ and TTPFeIIICl with no evidence for the formation of the phenoxide complexes. In this case electron transfer to yield the oxidized iron porphyrin and Superoxide ion is driven by the solvent polarity and the ability of the solvent to destroy Superoxide ion as it is formed.
Detection of Alkylperoxo and Ferryl, (Fe(IV)=O)(2+), Intermediates during the Reaction of tert-Butyl Hydroperoxide with Iron Porphyrins in Toluene Solution
Arasasingham, Ramesh D.,Cornman, Charles R.,Balch, Alan L.
, p. 7800 - 7805 (2007/10/02)
PFeII and PFeIIIOH (P is a porphyrin dianion) catalyze the decomposition of tert-butyl hydroperoxide in toluene solution without appreciable attack on the porphyrin ligand. (1)H NMR spectroscopic studies at low temperature (-70 deg C) give evidence for the formation of a high-spin, five-coordinate intermediate, PFeIIIOOC(CH3)3.On warming this decomposes to PFeIIIOH (P = tetramesitylporphyrin, TMP) or PFeIIIOFeIIIP (P = tetra-p-tolylporphyrin, TTP) with the formation of (TMP)FeIV=O as an observed intermediate in the first case.Treatment of PFeIIIOOC(CH3)3 at -70 deg C with N-methylimidazole (MeIm) yields the intermediate (MeIm)PFeIV=O.Organic products formed from this reaction are tert-butyl alcohol, di-tert-butyl peroxide, benzaldehyde, acetone, and benzyl-tert-butyl peroxide, which arise largely from a radical chain process initiated by the iron porphyrin but continuing without its intervention.
meso-Substituted Porphyrins, 4
Volz, Heinrich,Hassler, Michael,Schaeffer, Hermann
, p. 1265 - 1272 (2007/10/02)
2-Pyrryl-(3,5-dimethylphenyl)-carbinol, 2-pyrryl-(3,5-di-t-butyl-phenyl)-carbinol and 2-pyrryl-mesityl-carbinol are cyclised in acidic medium to the corresponding meso-tetraarylporphyrins.The meso-tetraarylporphyrins are transfered to the iron complexes.The reactions of the iron-porphyrins with OH(-) and H3CO(-) are studied and the products of these reactions are characterised. - Keywords: meso-Tetraarylporphyrins, meso-Tetraarylporphinatoiron(III) Complexes, meso-Tetramesitylporphinatoiron(III)methoxide, meso-Tetraarylporphinatoiron(III)hydroxides, μ-Oxo-bis(meso-tetraarylporphinatoiron(III))
Oxygenation Patterns for Iron(II) Porphyrins. Peroxo and Ferryl (FeIVO) Intermediates Detected by 1H Nuclear Magnetic Resonance Spectroscopy during the Oxygenation of (Tetramesitylporphyrin)iron(II)
Balch, Alan L.,Chan, Yee-Wai,Cheng, Ru-Jen,Mar, Gerd N. La,Latos-Grazynski, Lechoslaw,Renner, Mark W.
, p. 7779 - 7785 (2007/10/02)
The reaction between unligated (tetramesitylporphyrin)iron(II) (TMPFeII) and dioxygen in a toluene solution has been examined by 1H NMR spectroscopy.At -70 deg C, TMPFeII reacts with O2 to yield TMPFeIIIOOFeIIITMP that has spectroscopic properties similar to those of other peroxo-bridged complexes.On warming, TMPFeIIIOOFeIIITMP decomposes to yield a second intermediate (identified as TMPFeIVO) and TMPFeIIIOH, the final, stable product.TMPFeIIIOOFeIIITMP reacts with N-methylimidazole (N-MeIm) to produce (N-MeIm)TMPFeO2 and (N-MeIm)2TMPFeII.The former has been independently prepared from (N-MeIm)2TMPFeII and dioxygen at -50 deg C. TMPFeIVO reacts with N-MeIm to form (N-MeIm)TMPFeIVO that has been identified by comparison with other FeIVO complexes.TMPFeIVO reacts with triphenylphosphine at -50 deg C to yield triphenylphosphine oxide while TMPFeIIIOOFeIIITMP is unreactive toward triphenylphosphine under these conditions.TMPFeII is a catalyst for the oxidation of triphenylphosphine by dioxygen. 1H NMR spectra and resonance assignments for each species are described.
