Direct Kinetic Studies of Atom Transfer and Electron Transfer Reactions of Hydroperoxo and High-Valent Oxo Complexes of Chromium

Pestovsky, Oleg; Bakač, Andreja

doi:10.1021/ja0382213

Cited by 27 publications

(28 citation statements)

References 15 publications

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“…The L 1 (H 2 O)CrOOH 2+ /P(p-C 6 H 4 X) 3 reaction is acid catalyzed, as was already shown for PPh 3 in previous work [4]. At low [H + ] (≤ 0.02 M), the absorbance changes in the presence and absence of P(p-C 6 H 4 X) 3 were identical to within 5%, i. e. the overall stoichiometry ∆[Ru(NH 3 ) 5 py 2+ ]/[L 1 (H 2 O)CrOO 2+ ] 0 = 3.0 held.…”

Section: Approachsupporting

confidence: 77%

“…Every individual step has been observed and studied independently, and all the rate constants, except the one sought, have been determined in earlier work [2][3][4]. Every individual step has been observed and studied independently, and all the rate constants, except the one sought, have been determined in earlier work [2][3][4].…”

Section: Discussionmentioning

confidence: 99%

“…Recently, we have succeeded in determining the reactivities toward P(p-C 6 H 4 X) 3 of each individual form, L 1 (H 2 O)CrOOH 2+ and L 1 Cr V , present in the dynamic mixture [4]. Sequential stopped-flow experiments were used to measure the kinetics of L 1 Cr V reactions at the time of maximum conversion of L 1 (H 2 O)CrOOH 2+ to L 1 Cr V (20%).…”

Section: Introductionmentioning

confidence: 99%

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Competing Coordination and Oxygen Atom Transfer in a Reaction Between Triarylphosphines and a Chromium Hydroperoxo Complex

Pestovsky¹,

Bakač²

2005

BioInorganic Reaction Mechanisms

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A macrocyclic hydroperoxo chromium(III) complex, L 1 (H 2 O)CrOOH 2+ (L 1 = cyclam), reacts with triphenylphosphine and para-substituted derivatives in an acidcatalyzed O-atom transfer reaction in competition with intramolecular conversion to a Cr(V) complex. Oxygen atom transfer is complicated by another process, believed to be a rapid ligand exchange reaction that generates equilibrium amounts of less reactive L 1 (P(p-C 6 H 4 X) 3 )CrOOH 2+ . The fit of the data for O-atom transfer to the Hammett equation yields a reaction constant ρ = -0.24, consistent with a nucleophilic attack by P(p-C 6 H 4 X) 3 at one of the peroxo oxygens of the protonated hydroperoxo complex. The upper limit of <10 6 s -1 was estimated for the rate constant for hydrolysis of triphenylphosphine radical cation, PPh 3 •+ , in acidic 2:1 acetonitrile/H 2 O.

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Section: Approachsupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Competing Coordination and Oxygen Atom Transfer in a Reaction Between Triarylphosphines and a Chromium Hydroperoxo Complex

Pestovsky¹,

Bakač²

2005

BioInorganic Reaction Mechanisms

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“…Bakac and co-workers showed that a strongly oxidizing LCr V QO (L: trans- [14]aneN 4 ), generated from LCr III -OOH, reacts with triarylphosphines exhibiting a 1 : 1 stoichiometry and mixed second-order kinetics, and the Hammett plot for the reaction gives the slope (r) of À0.69, consistent with the electrophilic character of Cr(V). 26 2+ also provides clues to the reactivity differences of the active M n+ QO with its corresponding M n+ -OOH moieties.…”

Section: Electron Transfer Reactivity Of the Metal Oxo Moietiesmentioning

confidence: 99%

The reactivity of the active metal oxo and hydroxo intermediates and their implications in oxidations

2015

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While the significance of the redox metal oxo moieties has been fully acknowledged in versatile oxidation processes, active metal hydroxo moieties are gradually realized to play the key roles in certain biological oxidation events, and their reactivity has also been evidenced by related biomimic models. However, compared with the metal oxo moieties, the significance of the metal hydroxo moieties has not been fully recognized, and their relationships in oxidations remain elusive until recently. This review summarizes the reactivity of the metal oxo and hydroxo moieties in different oxidation processes including hydrogen atom transfer, oxygen atom transfer and electron transfer, and their reactivity similarities and differences have been discussed as well. Particularly, how the physicochemical properties like metal-oxygen bond order, net charge and potential of a redox metal ion affect its reactivity has also been presented based on available data. We hope that this review may provide new clues to understand the origins of the enzyme's choice on them in a specific event, to explain the elusive phenomena occurring in those enzymatic, homogeneous and heterogeneous oxidations, to design selective redox catalysts and control their reactivity.

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“…However, the fundamental electron-transfer properties of high-valent metal-oxo species have yet to be scrutinized mainly because of the thermal instability and high reactivity of high-valent metal-oxo species in nature. [17] In this context, mononuclear nonheme oxoiron(IV) intermediates, the structural and spectroscopic characterization of which has been well established recently, [18,19] have merited attention owing to their thermal stability.…”

Section: Introductionmentioning

confidence: 99%

Contrasting Effects of Axial Ligands on Electron‐Transfer Versus Proton‐Coupled Electron‐Transfer Reactions of Nonheme Oxoiron(IV) Complexes

Fukuzumi

Kotani

Suenobu

et al. 2009

Chemistry A European J

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The effects of axial ligands on electron-transfer and proton-coupled electron-transfer reactions of mononuclear nonheme oxoiron(IV) complexes were investigated by using [Fe(IV)(O)(tmc)(X)](n+) (1-X) with various axial ligands, in which tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is CH(3)CN (1-NCCH(3)), CF(3)COO(-) (1-OOCCF(3)), or N(3) (-) (1-N(3)), and ferrocene derivatives as electron donors. As the binding strength of the axial ligands increases, the one-electron reduction potentials of 1-X (E(red), V vs. saturated calomel electrode (SCE)) are more negatively shifted by the binding of the more electron-donating axial ligands in the order of 1-NCCH(3) (0.39) > 1-OOCCF(3) (0.13) > 1-N(3) (-0.05 V). Rate constants of electron transfer from ferrocene derivatives to 1-X were analyzed in light of the Marcus theory of electron transfer to determine reorganization energies (lambda) of electron transfer. The lambda values decrease in the order of 1-NCCH(3) (2.37) > 1-OOCCF(3) (2.12) > 1-N(3) (1.97 eV). Thus, the electron-transfer reduction becomes less favorable thermodynamically but more favorable kinetically with increasing donor ability of the axial ligands. The net effect of the axial ligands is the deceleration of the electron-transfer rate in the order of 1-NCCH(3) > 1-OOCCF(3) > 1-N(3). In sharp contrast to this, the rates of the proton-coupled electron-transfer reactions of 1-X are markedly accelerated in the presence of an acid in the opposite order: 1-NCCH(3) < 1-OOCCF(3) < 1-N(3). Such contrasting effects of the axial ligands on the electron-transfer and proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes are discussed in light of the counterintuitive reactivity patterns observed in the oxo transfer and hydrogen-atom abstraction reactions by nonheme oxoiron(IV) complexes (Sastri et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 19 181-19 186).

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Direct Kinetic Studies of Atom Transfer and Electron Transfer Reactions of Hydroperoxo and High-Valent Oxo Complexes of Chromium

Cited by 27 publications

References 15 publications

Competing Coordination and Oxygen Atom Transfer in a Reaction Between Triarylphosphines and a Chromium Hydroperoxo Complex

Competing Coordination and Oxygen Atom Transfer in a Reaction Between Triarylphosphines and a Chromium Hydroperoxo Complex

The reactivity of the active metal oxo and hydroxo intermediates and their implications in oxidations

Contrasting Effects of Axial Ligands on Electron‐Transfer Versus Proton‐Coupled Electron‐Transfer Reactions of Nonheme Oxoiron(IV) Complexes

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