Valence Tautomerization of High-Valent Manganese(V)-Oxo Corrole Induced by Protonation of the Oxo Ligand

Bougher, Curt J.; Liu, Shuo; Hicks, Scott D.; Abu‐Omar, Mahdi M.

doi:10.1021/jacs.5b09759

Cited by 54 publications

(74 citation statements)

References 45 publications

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“…In the work by Abu-Omar, addition of TFA also slightly decreased the H-atom abstraction rate for the corrole complex, although no other Lewis acids were tested in this study. 14 Our results strongly suggest that the identity of the Lewis acid is critical in determining the HAT reactivity of Mn IV (O-LA)(π-cation-radical) complexes (vide infra).…”

Section: Resultsmentioning

confidence: 66%

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High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

et al. 2016

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The addition of Lewis or Brönsted acids (LA = Zn(OTf)2, B(C6F5)3, HBArF, TFA) to the high-valent manganese—oxo complex MnV(O)(TBP8Cz) results in the stabilization of a valence tautomer MnIV(O-LA)(TBP8Cz•+). The ZnII and B(C6F5)3 complexes were characterized by manganese K-edge X-ray absorption spectroscopy (XAS). The position of the edge energies and the intensities of the pre-edge (1s to 3d) peaks confirm that the Mn ion is in the +4 oxidation state. Fitting of the extended X-ray absorption fine structure (EXAFS) region reveals 4 N/O ligands at Mn−Nave = 1.89 Å and a fifth N/O ligand at 1.61 Å, corresponding to the terminal oxo ligand. This Mn−O bond length is elongated compared to the MnV(O) starting material (Mn−O = 1.55 Å). The reactivity of MnIV(O-LA)(TBP8Cz−+) toward C−H substrates was examined, and it was found that H• abstraction from C−H bonds occurs in a 1:1 stoichiometry, giving a MnIV complex and the dehydrogenated organic product. The rates of C−H cleavage are accelerated for the MnIV(O-LA)(TBP8Cz•+) valence tautomer as compared to the MnV(O) valence tautomer when LA = ZnII, B(C6F5)3, and HBArF, whereas for LA = TFA, the C−H cleavage rate is slightly slower than when compared to MnV(O). A large, nonclassical kinetic isotope effect of kH/kD = 25–27 was observed for LA = B(C6F5)3 and HBArF, indicating that H-atom transfer (HAT) is the rate-limiting step in the C−H cleavage reaction and implicating a potential tunneling mechanism for HAT. The reactivity of MnIV(O-LA)(TBP8Cz•+) toward C−H bonds depends on the strength of the Lewis acid. The HAT reactivity is compared with the analogous corrole complex MnIV(O−H)(tpfc•+) recently reported.

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Section: Resultsmentioning

confidence: 66%

“…13 In 2015, Abu-Omar showed that addition of TFA to Mn V (O)(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)-corrolato 3− ) resulted in formation of the valence tautomer Mn IV (OH)(tpfc •+ ). 14 …”

Section: Introductionmentioning

confidence: 99%

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

et al. 2016

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“…Similar ‘valence tautomerizations’ have been observed in Mn V (O)-corrole systems, where protonation or binding a Lewis acid to the oxo moiety leads to reversible formation of a Mn IV (O–X)-(corrole-radical cation) complexes. 23 …”

Section: Resultsmentioning

confidence: 99%

Thermodynamics of Proton and Electron Transfer in Tetranuclear Clusters with Mn–OH₂/OH Motifs Relevant to H₂O Activation by the Oxygen Evolving Complex in Photosystem II

Reed

Agapie

2018

J. Am. Chem. Soc.

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We report the synthesis of site-differentiated heterometallic clusters with three Fe centers and a single Mn site that binds water and hydroxide in multiple cluster oxidation states. Deprotonation of FeIII/II3MnII–OH2 clusters leads to internal reorganization resulting in formal oxidation at Mn to generate FeIII/II3MnIII–OH. 57Fe Mӧssbauer spectroscopy reveals that oxidation state changes (three for FeIII/II3Mn–OH2 and four for FeIII/II3Mn–OH clusters) occur exclusively at the Fe centers; the Mn center is formally MnII when water is bound and MnIII when hydroxide is bound. Experimentally determined pKa (17.4) of the [FeIII2FeIIMnII–OH2] cluster and the reduction potentials of the [Fe3Mn–OH2] and [Fe3Mn–OH] clusters were used to analyze the O–H bond dissociation enthalpies (BDEO–H) for multiple cluster oxidation states. BDEO–H increases from 69, to 78, and 85 kcal/mol for the [FeIIIFeII2MnII-OH2], [FeIII2FeIIMnII-OH2], and [FeIII3MnII-OH2] clusters, respectively. Further insight of the proton and electron transfer thermodynamics of the [Fe3Mn–OHx] system was obtained by constructing a potential–pKa diagram; the shift in reduction potentials of the [Fe3Mn–OHx] clusters in the presence of different bases supports the BDEO–H values reported for the [Fe3Mn–OH2] clusters. A lower limit of the pKa for the hydroxide ligand of the [Fe3Mn–OH] clusters was estimated for two oxidation states. These data suggest BDEO–H values for the [FeIII2FeIIMnIII–OH] and [FeIII3MnIII–OH] clusters are greater than 93 and 103 kcal/mol, which hints to the high reactivity expected of the resulting [Fe3Mn=O] in this and related multinuclear systems.

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“…163 The comparative reactivity of these two valence tautomers was studied (Scheme 37). There was little or no difference for the two complexes in H-atom transfer rates with a substituted phenol as H-atom donor.…”

Section: Metal-oxo Porphyrinoid Complexes As Models For Biological Oxmentioning

confidence: 99%

Biomimetic Reactivity of Oxygen-Derived Manganese and Iron Porphyrinoid Complexes

2017

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Heme proteins utilize the heme cofactor, an iron porphyrin, to perform a diverse range of reactions including dioxygen binding and transport, electron transfer, and oxidation/oxygenations. These reactions share several, key metalloporphyrin intermediates, typically derived from dioxygen and its congeners such as hydrogen peroxide, and which are comprised of metal-dioxygen, metal-superoxo, metal-peroxo, and metal-oxo adducts. A wide variety of synthetic metalloporphyrinoid complexes have been synthesized to generate and stabilize these intermediates, and then employed to determine the spectroscopic features, structures, and reactivities of such species in controlled and well-defined environments. In this review, we summarize recent findings on the reactivity of these species with common porphyrinoid scaffolds employed for biomimetic studies. The proposed mechanisms of action are emphasized. The review is organized by structural type of metal-oxygen intermediate, and broken into subsections based on the metal (manganese, iron) and porphyrinoid ligand (porphyrin, corrole, corrolazine).

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Valence Tautomerization of High-Valent Manganese(V)-Oxo Corrole Induced by Protonation of the Oxo Ligand

Cited by 54 publications

References 45 publications

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

Thermodynamics of Proton and Electron Transfer in Tetranuclear Clusters with Mn–OH₂/OH Motifs Relevant to H₂O Activation by the Oxygen Evolving Complex in Photosystem II

Biomimetic Reactivity of Oxygen-Derived Manganese and Iron Porphyrinoid Complexes

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Valence Tautomerization of High-Valent Manganese(V)-Oxo Corrole Induced by Protonation of the Oxo Ligand

Cited by 54 publications

References 45 publications

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage

Thermodynamics of Proton and Electron Transfer in Tetranuclear Clusters with Mn–OH2/OH Motifs Relevant to H2O Activation by the Oxygen Evolving Complex in Photosystem II

Biomimetic Reactivity of Oxygen-Derived Manganese and Iron Porphyrinoid Complexes

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Thermodynamics of Proton and Electron Transfer in Tetranuclear Clusters with Mn–OH₂/OH Motifs Relevant to H₂O Activation by the Oxygen Evolving Complex in Photosystem II