Modeling TauD-<i><b>J</b></i>: A High-Spin Nonheme Oxoiron(IV) Complex with High Reactivity toward C–H Bonds

Biswas, Achintesh Narayan; Puri, Mayank; Meier, Katlyn K.; Oloo, Williamson N.; Rohde, Gregory T.; Bominaar, Emile L.; Münck, Eckard; Que, Lawrence

doi:10.1021/ja511757j

Cited by 155 publications

(233 citation statements)

References 38 publications

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“…Indeed comparable rate differences for the oxidation of 1-octene versus cyclohexane have been found for two other high-valent iron-oxo oxidants. The high-spin [Fe IV (O)(TQA] complex oxidizes 1-octene 16-fold faster than cyclohexane at −40 °C, 59 while the Fe V (O) oxidant generated from Fe(PyNMe 3 ) and AcOOH is about 40-fold faster in the oxidation of 1-octene than cyclohexane. 54 73 .…”

Section: Resultsmentioning

confidence: 99%

Equilibrating (L)Fe^III–OOAc and (L)Fe^V(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H₂O₂ and AcOH

et al. 2017

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Inspired by the remarkable chemistry of the family of Rieske oxygenase enzymes, nonheme iron complexes of tetradentate N4 ligands have been developed to catalyze hydrocarbon oxidation reactions using H2O2 in the presence of added carboxylic acids. The observation that the stereo- and enantioselectivity of the oxidation products can be modulated by the electronic and steric properties of the acid implicates an oxidizing species that incorporates the carboxylate moiety. Frozen solutions of these catalytic mixtures generally afford two S = ½ intermediates, a highly anisotropic g2.7 subset (gmax = 2.58 to 2.78 and Δg = 0.85 – 1.2) that we assign to an FeIII–OOAc species and the less anisotropic g2.07 subset (g = 2.07, 2.01, and 1.96 and Δg ~ 0.11) we associate with an FeV(O)(OAc) species. Kinetic studies on the reactions of iron complexes supported by the TPA (tris(pyridyl-2-methyl)amine) ligand family with H2O2/AcOH or AcOOH at −40 °C reveal the formation of a visible chromophore at 460 nm, which persists in a steady state phase and then decays exponentially upon depletion of the peroxo oxidant with a rate constant that is substrate independent. Remarkably, the duration of this steady state phase can be modulated by the nature of the substrate and its concentration, which is a rarely observed phenomenon. A numerical simulation of this behavior as a function of substrate type and concentration affords a kinetic model in which the two intermediates exist in a dynamic equilibrium that is modulated by the electronic properties of the supporting ligands. This notion is supported by EPR studies of the reaction mixtures. Importantly, these studies unambiguously show that the g2.07 species, and not the g2.7 species, is responsible for substrate oxidation in the (L)FeII/H2O2/AcOH catalytic system. Instead the g2.7 species appears to be off-pathway and serves as a reservoir for the g2.07 species. These findings will be helpful not only for the design of regio- and stereo-specific nonheme iron oxidation catalysts but also for providing insight into the mechanisms of the remarkably versatile oxidants formed by nature’s most potent oxygenases.

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Section: Resultsmentioning

confidence: 99%

Equilibrating (L)Fe^III–OOAc and (L)Fe^V(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H₂O₂ and AcOH

et al. 2017

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“…19,20 Recently, one high spin Fe IV O complex, [Fe IV (O)(TQA)(NCMe)] 2+ (TQA = tris(2-quinolylmethyl)amine), was found to be significantly more reactive toward HAT than other S = 2 Fe IV O complexes, and was also found to effect alkene epoxidation. 21 We wish to investigate whether the reactivity of ferryl complexes can be tuned by modification of the steric and electronic properties of ligands, and whether the reactivity of such complexes can be improved while maintaining thermal stability. For this purpose, we chose to modify/derivatize the N4Py ligand framework.…”

Section: ■ Introductionmentioning

confidence: 99%

Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions

et al. 2015

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Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

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“…Comparison of the HAT reactivities of 1 and other oxoiron(IV) complexes (Tables 1 and S4) shows that the rate of cyclohexane oxidation by 1 at −40 °C (0.01 M −1 s −1 ) is only an order of magnitude lower than that of the two most reactive complexes reported to date; namely, the S = 2 [Fe IV (O)(TQA)(CH 3 CN)] 2+ (0.37 M −1 s −1 ) [13] and S = 1 [Fe IV (O)(Me 3 NTB)(CH 3 CN)] 2+ (0.25 M −1 s −1 ) [14] complexes. In particular, the closely related S = 1 [Fe IV (O)(TMC)(CH 3 CN)] 2+ complex does not react at all with cyclohexane even at 25 °C.…”

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A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N₃O Macrocyclic Ligand

et al. 2017

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The sluggish oxidants, [FeIV(O)(TMC)(CH3CN)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [FeIV(O)(d12-TMCN)(OTf)]+ (3d; d12-TMCN = 1,4,7,11-tetra-d3-methyl-1,4,7,11-tetraazacyclotetradecane), are transformed into a highly reactive oxidant, [FeIV(O)(TMCO)(OTf)]+ (1; TMCO = 4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane), upon replacement of a -NMe donor in the TMC and TMCN ligands by an O-atom. A rate enhancement of 5 – 6 orders of magnitude in both H-atom and O-atom transfer reactions is observed upon oxygen incorporation into the macrocyclic ligand and can be explained based upon the higher electrophilicity of the iron center and the higher availability of the more reactive S = 2 state in 1. This rationalizes nature’s preference for using O-rich ligand environments for the hydroxylation of strong C-H bonds in enzymatic reactions.

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Modeling TauD-J: A High-Spin Nonheme Oxoiron(IV) Complex with High Reactivity toward C–H Bonds

Cited by 155 publications

References 38 publications

Equilibrating (L)Fe^III–OOAc and (L)Fe^V(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H₂O₂ and AcOH

Equilibrating (L)Fe^III–OOAc and (L)Fe^V(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H₂O₂ and AcOH

Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N₃O Macrocyclic Ligand

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Modeling TauD-J: A High-Spin Nonheme Oxoiron(IV) Complex with High Reactivity toward C–H Bonds

Cited by 155 publications

References 38 publications

Equilibrating (L)FeIII–OOAc and (L)FeV(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H2O2 and AcOH

Equilibrating (L)FeIII–OOAc and (L)FeV(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H2O2 and AcOH

Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3O Macrocyclic Ligand

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Equilibrating (L)Fe^III–OOAc and (L)Fe^V(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H₂O₂ and AcOH

Equilibrating (L)Fe^III–OOAc and (L)Fe^V(O) Species in Hydrocarbon Oxidations by Bio-Inspired Nonheme Iron Catalysts Using H₂O₂ and AcOH

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N₃O Macrocyclic Ligand