<i>cis</i> Donor Influence on O–O Bond Lability in Iron(III) Hydroperoxo Complexes: Oxidation Catalysis and Ligand Transformation

Wegeberg, Christina; Browne, Wesley R.; McKenzie, Christine J.

doi:10.1021/acs.inorgchem.9b00247

Cited by 11 publications

(26 citation statements)

References 72 publications

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“…9) decompositions of CyOOH. Notably, cycloxexanol(A) could be oxidized into cyclohexanone (K) by H 2 O 2 likely via a radical mechanism (Eqs.10 and 11), [42] which was well consistent with the present obseravtion on PhÀ FeCl catalyst.…”

Section: Catalytic Performancesupporting

confidence: 88%

Reduced Amino Acid Schiff Base‐Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide

et al. 2021

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The reduced amino acid Schiff base ligands have been prepared and were coordinated with ferric chloride to generate the iron (III) complexes. The ligands and complexes have been characterized using FT-IR, UV-vis, elemental analysis, ICP-AES analysis, mass spectra etc. After the structural characterization, these complexes were applied for the oxidation of cyclohexane using hydrogen peroxide as the oxidant under mild conditions. The activity tests showed that the L-phenylalanine-derived reduced Schiff base iron(III) complex(PhÀ FeCl) afforded the highest yield of cyclohexanol and cyclohexanone(total yield up to 23.2 %).Notably, the PhÀ FeCl complex catalyzes the reaction via a heterogeneous approach, allowing the complex to be separated and recycled conveniently after the oxidation reaction. Besides, the PhÀ FeCl catalyst can also be extended for the selective oxidation of other alkanes and aromatics into alcohols, ketones and phenols etc. Finally, the reaction mechanism of cyclohexane oxidation on the iron(III) complex was proposed as well by the free radical inhibitors and EPR study of active intermediates.

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Section: Catalytic Performancesupporting

confidence: 88%

Reduced Amino Acid Schiff Base‐Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide

et al. 2021

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“…The iron(II) complexes of the neutral ligands metpen, ettpen, bztpen, and tpen are oxidized according to eqs 1a and 1b. Equation 1b only applies to the iron(III) complexes of tpena and deprotonated tpenOH ([Fe III (tpenO)] 2+ is spontaneously generated on dissolution of [Fe II Cl(tpenOH)]-(PF 6 ) under ambient conditions 58 ). Given the pK a of pyridinium (ca.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…52,53,55 Equivalent (N4O)Fe III OOH/R complexes oxidize methanol rapidly, precluding the use of this solvent for a determination of comparable spectroscopic data, and intramolecular ligand amine or aryl oxygenation reactions occur. 56,58 To date spectroscopic data have been gathered for only one biomimetic cis carboxylato iron peroxide which is supported by N,N,N′-tris(2-pyridylmethyl)ethylenediamine-N′-acetate (tpena). 43,57−60 The Rtpen system (Scheme 2), which includes tpena, offers a convenient scaffold for probing the importance of the position cis to the oxo ligand.…”

Section: ■ Introductionmentioning

confidence: 99%

Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C–H Oxidation by a cis Donor and Variation of the Second Coordination Sphere

et al. 2021

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A series of iron(IV) oxo complexes, which differ in the donor (CH 2 py or CH 2 COO − ) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The ν FeO values of 832 ± 2 cm −1 indicate similar Fe IV O bond strengths; however, different reactivities toward C−H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (k H /k D = 30−66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C−H oxidation by the most potent complex, that with a cis-carboxylate donor, [Fe IV O(Htpena)] 2+ , is observed. Supramolecular assistance by the first and second coordination spheres in activating the substrate is proposed. The lifetime of this complex in the absence of a C−H substrate is the shortest (at pH 2, 3 h vs up to 1.3 days for the most stable complex), implying that slow water oxidation is a competing background reaction. The iron(IV)O complex bearing an alcohol moiety in the second coordination sphere displays significantly shorter lifetimes due to a competing selective intramolecular oxidation of the ligand.

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“…In contrast, synthetic examples of Fe(III)hydroperoxo intermediates are almost always generated with exogenous reducing or acid equivalents. [41][42][43][44][45][46][47][48][49][50][51][52] There are effectively no examples of well-defined Fe(III)-hydroperoxo intermediates generated via biomimetic H-atom transfer from a designed secondary coordination sphere, with one lone example arising from adventitious activation of a supporting ligand. 53 Synthetic systems where designed ancillary ligands can donate both protons and electrons have been an area of increasing interest.…”

Section: Enzymaticmentioning

confidence: 99%

“…78 The observed O-O stretching frequency compares favorably with related Fehydroperoxo complexes. 41,42,[45][46][47][48][49][50][51][52]76 Additionally, two features are seen at 3420 cm −1 and 3230 cm −1 , which could be assigned either as two N-H stretches or as an N-H and O-H stretch for an Fe(III)superoxo and Fe(III)-hydroperoxo respectively (Figure 3). Given the much higher intensity of the feature at 3420 cm −1 relative to the feature at 3230 cm −1 , and the dramatically higher stretching frequency for one of these features versus νNH in 1, the most reasonable conclusion is that these stretches do not both arise from N-H moieties, but rather are an N-H and an O-H stretch, consistent with an Fe(III)hydroperoxo complex.…”

Section: Characterization Of Intermediatementioning

confidence: 99%

Direct Aerobic Generation of a Ferric Hydroperoxo Intermediate via a Preorganized Secondary Coordination Sphere

Jesse

Anferov

Collins³

et al. 2021

Preprint

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Enzymes exert control over the reactivity of metal centers with precise tuning of the secondary coordination sphere of active sites. One particularly elegant illustration of this principle is in the controlled delivery of proton and electron equivalents in order to activate abundant but kinetically inert oxidants such as O2 for oxidative chemistry. Chemists have drawn inspiration from biology in designing molecular systems where the secondary coordination sphere can shuttle protons or electrons to substrates. However, a biomimetic activation of O2 requires the transfer of both protons and electrons, and molecular systems where ancillary ligands are designed to provide both of these equivalents are comparatively rare. Here we report the use of a dihydrazonopyrrole (DHP) ligand complexed to Fe to perform exactly such a biomimetic activation of O2. In the presence of O2, this complex directly generates a high spin Fe(III)-hydroperoxo intermediate which features a DHP • ligand radical via ligand-based transfer of an H-atom. This system displays oxidative reactivity and ultimately releases hydrogen peroxide, providing insight on how secondary coordination sphere interactions influence the evolution of oxidizing intermediates in Fe-mediated aerobic oxidations.

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cis Donor Influence on O–O Bond Lability in Iron(III) Hydroperoxo Complexes: Oxidation Catalysis and Ligand Transformation

Cited by 11 publications

References 72 publications

Reduced Amino Acid Schiff Base‐Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide

Reduced Amino Acid Schiff Base‐Iron(III) Complexes Catalyzing Oxidation of Cyclohexane with Hydrogen Peroxide

Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C–H Oxidation by a cis Donor and Variation of the Second Coordination Sphere

Direct Aerobic Generation of a Ferric Hydroperoxo Intermediate via a Preorganized Secondary Coordination Sphere

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