Electrochemical oxidation of spin-admixed S = 5/2, 3/2 iron(III) porphyrins: in situ characterization by deuterium NMR spectroscopy

Boersma, Arden D.; Goff, Harold M.

doi:10.1021/ic00180a009

Cited by 23 publications

(7 citation statements)

References 3 publications

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“…In this sense, it reflects a more general phenomenon observed for iron-porphyrin complexes: the strong influence of axial ligation on the stabilization of higher oxidation states of Fe (indicated experimentally by numerous electrochemical studies, [32,33,38,41,[43][44][45] and further substantiated by theoretical calculations).…”

Section: A C H T U N G T R E N N U N G (Pc + )(O)] (Which May Be Convmentioning

confidence: 59%

“…When X is a weak ligand (e.g., ClO 4 À or CF 3 SO 3 À ), the relationship E8' Fe IV /Fe III @ E8' PC + /P was found experimentally. [32,33,49] The introduction of ligands offering moderate stabilization of Fe IV (e.g., Cl [36,37] ) was found to lower the E8' Fe IV /Fe III potential, such that E8' Fe IV /Fe III % E8' PC + /P . [38,43,44,50] Finally, when consider-…”

Section: A C H T U N G T R E N N U N G (Pc + )(O)] (Which May Be Convmentioning

confidence: 99%

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Mechanistic Studies on Peroxide Activation by a Water‐Soluble Iron(III)–Porphyrin: Implications for OO Bond Activation in Aqueous and Nonaqueous Solvents

Wolak

Eldik

2007

Chemistry A European J

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The reactions of a water-soluble iron(III)-porphyrin, [meso-tetrakis(sulfonatomesityl)porphyrinato]iron(III), [Fe(III)(tmps)] (1), with m-chloroperoxybenzoic acid (mCPBA), iodosylbenzene (PhIO), and H(2)O(2) at different pH values in aqueous methanol solutions at -35 degrees C have been studied by using stopped-flow UV/Vis spectroscopy. The nature of the porphyrin product resulting from the reactions with all three oxidants changed from the oxo-iron(IV)-porphyrin pi-cation radical [Fe(IV)(tmps(*+))(O)] (1(++)) at pH<5.5 to the oxo-iron(IV)-porphyrin [Fe(IV)(tmps)(O)] (1(+)) at pH>7.5, whereas a mixture of both species was formed in the intermediate pH range of 5.5-7.5. The observed reactivity pattern correlates with the E degrees' versus pH profile reported for 1, which reflects pH-dependent changes in the relative positions of E degrees'(Fe(IV)/Fe(III) ) and E degrees'(P(*+)/P) for metal- and porphyrin-centered oxidation, respectively. On this basis, the pH-dependent redox equilibria involving 1(++) and 1(+) are suggested to determine the nature of the final products that result from the oxidation of 1 at a given pH. The conclusions reached are extended to water-insoluble iron(III)-porphyrins on the basis of literature data concerning the electrochemical and catalytic properties of [Fe(III)(P)(X)] species in nonaqueous solvents. Implications for mechanistic studies on [Fe(P)]-catalyzed oxidation reactions are briefly addressed.

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Section: A C H T U N G T R E N N U N G (Pc + )(O)] (Which May Be Convmentioning

confidence: 59%

Section: A C H T U N G T R E N N U N G (Pc + )(O)] (Which May Be Convmentioning

confidence: 99%

Mechanistic Studies on Peroxide Activation by a Water‐Soluble Iron(III)–Porphyrin: Implications for OO Bond Activation in Aqueous and Nonaqueous Solvents

Wolak

Eldik

2007

Chemistry A European J

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“…29,33,39 An increase of the pyrrole and furan resonance shifts on warming reflects the anti-Curie behavior expected for such an electronic structure (Figure 5). 41 The reduction of (OTPP)Fe III (CN) 2 by cyanide has the precedence in the reactivity of regular iron(III) porphyrins. 42 Reaction with Carbanions.…”

Section: Resultsmentioning

confidence: 99%

Iron Complexes of 5,10,15,20-Tetraphenyl-21-oxaporphyrin

Pawlicki

Latos‐Grażyński

2002

Inorg. Chem.

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The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.

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“…The bond length between the metal and the pyrrole nitrogens is most distinctive for differentiation between high-spin (Fe−N ≥ 2.06 Å) and intermediate- or low-spin (Fe−N ≤ 2.00 Å) iron(III) porphyrins. 37a,40a This is however not expected in the present case, since the d x 2 - y 2 orbital is not occupied in both high- and low-spin Mn(III). It is well documented that the metal−nitrogen bond lengths are very similar (Mn−N ∼ 2.00 Å) in 5- and 6-coordinated Mn(III) porphyrins 40a,b in a Mn(III) porphyrin cation radical 15 and even in Mn(IV) porphyrins 40c…”

Section: Referencesmentioning

confidence: 99%

Spin Transition in a Manganese(III) Porphyrin Cation Radical, Its Transformation to a Dichloromanganese(IV) Porphyrin, and Chlorination of Hydrocarbons by the Latter

et al. 1997

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Chemical oxidation of (TMP)Mn(III)(Cl) (TMP = the tetramesitylporphyrinato dianion) by Fe(ClO(4))(3) leads to the porphyrin-oxidized product (TMP(*)(+))Mn(III)(ClO(4))(2). Magnetic measurements and EPR spectroscopy show that the total spin of the complex changes from S = (5)/(2) at high temperature to S = (3)/(2) at low temperature. Ligand exchange of the perchlorato ligands in (TMP(*)(+))Mn(III)(ClO(4))(2) by chloride anions is accompanied by a change of the oxidation site from porphyrin to metal, resulting in (TMP)Mn(IV)(Cl)(2). This high-valent-metal complex can effect chlorine atom transfer to olefins, as well as to dimedone and chlorodimedone, natural substrates of chloroperoxidases.

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Electrochemical oxidation of spin-admixed S = 5/2, 3/2 iron(III) porphyrins: in situ characterization by deuterium NMR spectroscopy

Cited by 23 publications

References 3 publications

Mechanistic Studies on Peroxide Activation by a Water‐Soluble Iron(III)–Porphyrin: Implications for OO Bond Activation in Aqueous and Nonaqueous Solvents

Mechanistic Studies on Peroxide Activation by a Water‐Soluble Iron(III)–Porphyrin: Implications for OO Bond Activation in Aqueous and Nonaqueous Solvents

Iron Complexes of 5,10,15,20-Tetraphenyl-21-oxaporphyrin

Spin Transition in a Manganese(III) Porphyrin Cation Radical, Its Transformation to a Dichloromanganese(IV) Porphyrin, and Chlorination of Hydrocarbons by the Latter

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