Selective electrocatalysis of alkene oxidations in aqueous media. Electrochemical and spectral characterization of oxo-ferryl porphyrin, oxo-ferryl porphyrin radical cation and their reaction products with alkenes at room temperature

Liu, Mao‐Huang; Su, Yuhlong Oliver

doi:10.1016/s0022-0728(98)00114-4

Cited by 30 publications

(9 citation statements)

References 22 publications

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“…16a There is an apparent difference in potential of 750 mV between the redox couples [Fe V (O) − /Fe IV (O) 2− ] at pH 7 and [Fe IV (O) 2− /Fe III (OH) 2− ] at pH 12. After correcting for the pH difference based on the observation of a [Fe IV (O)] 2− /[Fe III (OH 2 ) 2 ] − couple between pH 7 and 10, we estimate a redox potential of 0.9 V versus NHE at pH 7, decreasing the redox potential gap to ∼300 mV.…”

Section: Resultsmentioning

confidence: 99%

“…For comparison, the corresponding heme analogues that serve as models of Cpd I and Cpd II exhibit a difference of ∼250 mV. 16b …”

Section: Resultsmentioning

confidence: 99%

“…This moderate BDE of [Fe III (bTAML)O−H] 2− (∼83 kcal/mol) is similar to that of nonheme iron complexes such as [Fe III (N4Py)O−H] 2+ (∼78 kcal/mol) 18 (N4Py = N , N -bis(2-pyridylmethyl)- N -bis(2-pyridyl)methylamine) but lower than their heme analogues ([Fe III (TMP)O−H] (∼88 kcal/mol) 5i (TMP = 5,10,15,20-tetramesitylporphyrin) and [Fe III (TMPS)O−H] (∼90 kcal/mol); TMPS = 5,10,15,20-tetramesitylporphyrinoctasulfonate). 16b,19a On the other hand, the oxoiron(V) complex 3 is known to react with strong C−H bonds like cyclohexane. 8a The Fe IV O−H BDE of [(bTAML)Fe IV OH] − is estimated to be about 99 kcal/mol, 20 which is roughly the same as that for the Compound I mimic [(4-TMPyP +· )Fe IV (O)] (4-TMPyP = 5,10,15,20-tetrakis( N -methyl-4-pyridinium)porphyrin tetracation) with an Fe IV O−H BDE of 100 kcal/mol.…”

Section: Resultsmentioning

confidence: 99%

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Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

et al. 2017

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In this report we compare the geometric and electronic structures and reactivities of [FeV(O)]− and [FeIV(O)]2− species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the Fe=O vibration of the [FeIV(O)]2− complex 2 is at 798 cm−1, compared to 862 cm−1 for the corresponding [FeV(O)]− species 3, a 64 cm−1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe=O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe=O bond length of 1.59 Å, which is 0.05 Å shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [FeIV(O)]2−/[FeIII(OH)]2− and [FeV(O)]−/[FeIV(O)]2− couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.

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Section: Resultsmentioning

confidence: 99%

“…For comparison, the corresponding heme analogues that serve as models of Cpd I and Cpd II exhibit a difference of ∼250 mV. 16b …”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

et al. 2017

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“…Under this condition, the slope of the linear response in Fig. 9B, which can be described as 2k 4 [TMPyPFe(IV) = O], was used to calculate the apparent second-order rate constant for the reaction of TMPyPFe(IV) = O with luminol. The value k 4 was estimated to be 1.31 Â 10 4 /mol/L/s.…”

Section: Reaction Of the New Transient Species With Luminolmentioning

confidence: 99%

“…Fe(IV) = O (TMP = meso-tetramesityl porphyrin). More recently, Su and Liu (4) reported that both the TSMPFe(IV) = O and the (TSMP) . Fe(IV) = O have been generated by a one-electron and two-electron electrochemical-oxidation of Fe(III)TSMP (TSMP = meso-tetrakis-3-sulphonatomesityl porphyrin).…”

Section: Introductionmentioning

confidence: 99%

Transient formation of the oxo–iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)porphyrin with hydrogen peroxide in aqueous solution

Saha¹,

Karmaker²,

Tamagake³

2003

Luminescence

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The reaction of iron(III) tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphyrin (Fe(III)TMPyP) with hydrogen peroxide (H(2)O(2)) and the catalytic activity of the reaction intermediates on the luminescent peroxidation of luminol in aqueous solution were studied by using a double-mixing stopped-flow system. The observed luminescence intensities showed biphasic decay depending on the conditions. The initial flashlight decayed within <1 s followed by a sustained emission for more than 30 s. Computer deconvolution of the time-resolved absorption spectra under the same conditions revealed that the initial flashlight appeared during the formation of the oxo-iron(IV) porphyrin, TMPyPFe(IV) = O, which is responsible for the sustained emission. The absorption spectra 0.0-0.5 s did not reproduce well by a simple combination of the two spectra of Fe(III)TMPyP and TMPyPFe(IV) = O, indicating that transient species was formed at the initial stage. Addition of uric acid (UA) caused a significant delay in the initiation of the luminol emission as well as in the formation of the TMPyPFe(IV) = O. Both of them were completely diminished in the presence of UA equimolar with H(2)O(2), while mannitol had no effect at all. The delay of the light emission as well as the appearance of TMPyPFe(IV) = O was directly proportional to the [UA](0) but other kinetic profiles were not changed significantly. Based on these observations and the kinetic analysis, we confirmed the involvement of the oxo-iron(IV) porphyrin radical cation, (TMPyP)(.+)Fe(IV) = O, as an obligatory intermediate in the rate-determining step of the overall reaction, Fe(III)TMPyP + H(2)O(2) --> TMPyPFe(IV) = O, with a rate constant of k = 4.3 x 10(4)/mol/L/s. The rate constants for the reaction between the (TMPyP)(.+)Fe(IV) = O and luminol, and between the TMPyPFe(IV) = O and luminol were estimated to be 3.6 x 10(6)/mol/L/s and 1.31 x 10(4)/mol/L/s, respectively.

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Kinetic simulation studies on the transient formation of the oxo‐iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)‐porphyrin with hydrogen peroxide in aqueous solution

2003

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High-valent oxo-iron(IV) species are commonly proposed as the key intermediates in the catalytic mechanisms of iron enzymes. Water-soluble iron(III) tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphyrin (Fe(III)TMPyP) has been used as a model of heme-enzyme to catalyse the hydrogen peroxide (H(2)O(2)) oxidation of various organic compounds. However, the mechanism of the reaction of Fe(III)TMPyP with H(2)O(2) has not been fully established. In this study, we have explored the kinetic simulation of the reaction of Fe(III)TMPyP with H(2)O(2) and of the catalytic reactivity of FeTMPyP in the luminescent peroxidation of luminol. According to the mechanism that has been established in this work, Fe(III)TMPyP is oxidized by H(2)O(2) to produce (TMPyP)(*+)Fe(IV)[double bond]O (k1 = 4.5 x 10(4)/mol/L/s) as a precursor of TMPyPFe(IV)[double bond]O. The intermediate, (TMPyP)(*+)Fe(IV)[double bond]O, represented nearly 2% of Fe(III)TMPyP but it does not accumulate in sufficient concentration to be detected because its decay rate is too fast. Kinetic simulations showed that the proposed scheme is capable of reproducing the observed time courses of FeTMPyP in various oxidation states and the decay profiles of the luminol chemiluminescence. It also shows that (TMPyP)(*+)Fe(IV)[double bond]O is 100 times more reactive than TMPyPFe(IV)[double bond]O in most of the reactions. These two species are responsible for the initial sharp and the sustained luminol emissions, respectively.

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Selective electrocatalysis of alkene oxidations in aqueous media. Electrochemical and spectral characterization of oxo-ferryl porphyrin, oxo-ferryl porphyrin radical cation and their reaction products with alkenes at room temperature

Cited by 30 publications

References 22 publications

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

Transient formation of the oxo–iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)porphyrin with hydrogen peroxide in aqueous solution

Kinetic simulation studies on the transient formation of the oxo‐iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)‐porphyrin with hydrogen peroxide in aqueous solution

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Selective electrocatalysis of alkene oxidations in aqueous media. Electrochemical and spectral characterization of oxo-ferryl porphyrin, oxo-ferryl porphyrin radical cation and their reaction products with alkenes at room temperature

Cited by 30 publications

References 22 publications

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with FeV═O and FeIV═O Units

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with FeV═O and FeIV═O Units

Transient formation of the oxo–iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)porphyrin with hydrogen peroxide in aqueous solution

Kinetic simulation studies on the transient formation of the oxo‐iron(IV) porphyrin radical cation during the reaction of iron(III) tetrakis‐5,10,15,20‐(N‐methyl‐4‐pyridyl)‐porphyrin with hydrogen peroxide in aqueous solution

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Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units