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David P. Goldberg - One of the best experts on this subject based on the ideXlab platform.
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high valent manganese oxo Valence Tautomers and the influence of lewis bronsted acids on c h bond cleavage
Inorganic Chemistry, 2016Co-Authors: Regina A. Baglia, Courtney M. Krest, Tzuhsiung Yang, Pannee Leeladee, David P. GoldbergAbstract:The addition of Lewis or Bronsted 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 A and a fifth N/O ligand at 1.61 A, corresponding to the terminal oxo ligand. This Mn–O bond length is elongated compared to the MnV(O) starting material (Mn–O = 1.55 A). 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)(T...
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High-Valent Manganese–Oxo Valence Tautomers and the Influence of Lewis/Brönsted Acids on C–H Bond Cleavage
2016Co-Authors: Regina A. Baglia, Courtney M. Krest, Tzuhsiung Yang, Pannee Leeladee, David P. GoldbergAbstract: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 (J. Am. Chem. Soc. 2015, 137, 14481–14487)
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strong inhibition of o atom transfer reactivity for mniv o π radical cation lewis acid versus mnv o porphyrinoid complexes
Journal of the American Chemical Society, 2015Co-Authors: Jan Paulo T Zaragoza, Regina A. Baglia, Maxime A. Siegler, David P. GoldbergAbstract:The oxygen atom transfer (OAT) reactivity of two Valence Tautomers of a MnV(O) porphyrinoid complex was compared. The OAT kinetics of MnV(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato3–) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV–vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 104 M–1 s–1. Characterization of the OAT transition state analogues MnIII(OPPh3)(TBP8Cz) and MnIII(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A Valence Tautomer of the closed-shell MnV(O)(TBP8Cz) can be stabilized by the addition of Lewis and Bronsted acids, resulting in the open-shell MnIV(O)(TBP8Cz•+):LA (LA = ZnII, B(C6F5)3, H+) complexes. These MnIV(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10–3 – 8.7 M–1 s–1), contrasting the previously observed rate increase of H-atom transfer (HAT) for MnIV(O)(TBP8Cz•+):LA ...
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Activation of a High-Valent Manganese–Oxo Complex by a Nonmetallic Lewis Acid
2015Co-Authors: Regina A. Baglia, Maximilian Dürr, Ivana Ivanović-burmazović, David P. GoldbergAbstract:The reaction of a manganese(V)–oxo porphyrinoid complex with the Lewis acid B(C6F5)3 leads to reversible stabilization of the Valence Tautomer MnIV(O)(π-radical cation). The latter complex, in combination with B(C6F5)3, reacts with ArO–H substrates via formal hydrogen-atom transfer and exhibits dramatically increased reaction rates over the MnV(O) starting material
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Strong Inhibition of O‑Atom Transfer Reactivity for MnIV(O)(π-Radical-Cation)(Lewis Acid) versus MnV(O) Porphyrinoid Complexes
2015Co-Authors: Jan Paulo T. Zaragoza, Regina A. Baglia, Maxime A. Siegler, David P. GoldbergAbstract:The oxygen atom transfer (OAT) reactivity of two Valence Tautomers of a MnV(O) porphyrinoid complex was compared. The OAT kinetics of MnV(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato3–) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV–vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 104 M–1 s–1. Characterization of the OAT transition state analogues MnIII(OPPh3)(TBP8Cz) and MnIII(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A Valence Tautomer of the closed-shell MnV(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell MnIV(O)(TBP8Cz•+):LA (LA = ZnII, B(C6F5)3, H+) complexes. These MnIV(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10–3 – 8.7 M–1 s–1), contrasting the previously observed rate increase of H-atom transfer (HAT) for MnIV(O)(TBP8Cz•+):LA with phenols. A Hammett analysis showed that the OAT reactivity for MnIV(O)(TBP8Cz•+):LA is influenced by the Lewis acid strength. Spectral redox titration of MnIV(O)(TBP8Cz•+):ZnII gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its Valence Tautomer MnV(O)(TBP8Cz) (Ered = −0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) Valence Tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of Valence Tautomers such as MV(O)(porph) versus MIV(O)(porph•+) (M = Mn or Fe) found in heme enzymes
Kelly J Gaffney - One of the best experts on this subject based on the ideXlab platform.
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charge and spin state characterization of cobalt bis o dioxolene Valence Tautomers using co kβ x ray emission and l edge x ray absorption spectroscopies
Inorganic Chemistry, 2017Co-Authors: Winnie H Liang, Thomas Kroll, Dennis Nordlund, Tsuchien Weng, Dimosthenis Sokaras, Cortlandt G Pierpont, Kelly J GaffneyAbstract:The Valence Tautomeric states of Co(phen)(3,5-DBQ)2 and Co(tmeda)(3,5-DBQ)2, where 3,5-DBQ is either the semiquinone (SQ–) or catecholate (Cat2–) form of 3,5-di-tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of Valence Tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature Valence Tautomer can be described as a low-spin CoIII configuration and the high-temperature Valence Tautomer as a high-spin CoII configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature Valence Tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. Th...
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Charge and Spin-State Characterization of Cobalt Bis(o‑dioxolene) Valence Tautomers Using Co Kβ X‑ray Emission and L‑Edge X‑ray Absorption Spectroscopies
2016Co-Authors: Winnie H Liang, Thomas Kroll, Dennis Nordlund, Tsuchien Weng, Dimosthenis Sokaras, Cortlandt G Pierpont, Kelly J GaffneyAbstract:The Valence Tautomeric states of Co(phen)(3,5-DBQ)2 and Co(tmeda)(3,5-DBQ)2, where 3,5-DBQ is either the semiquinone (SQ–) or catecholate (Cat2–) form of 3,5-di-tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of Valence Tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature Valence Tautomer can be described as a low-spin CoIII configuration and the high-temperature Valence Tautomer as a high-spin CoII configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature Valence Tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. The nature and strength of the magnetic exchange interaction between the cobalt center and SQ– in cobalt Valence Tautomers is discussed in view of the effective spin at the Co site from Kβ XES and the molecular spin moment from magnetic susceptibility measurements
Regina A. Baglia - One of the best experts on this subject based on the ideXlab platform.
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high valent manganese oxo Valence Tautomers and the influence of lewis bronsted acids on c h bond cleavage
Inorganic Chemistry, 2016Co-Authors: Regina A. Baglia, Courtney M. Krest, Tzuhsiung Yang, Pannee Leeladee, David P. GoldbergAbstract:The addition of Lewis or Bronsted 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 A and a fifth N/O ligand at 1.61 A, corresponding to the terminal oxo ligand. This Mn–O bond length is elongated compared to the MnV(O) starting material (Mn–O = 1.55 A). 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)(T...
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strong inhibition of o atom transfer reactivity for mniv o π radical cation lewis acid versus mnv o porphyrinoid complexes
Journal of the American Chemical Society, 2015Co-Authors: Jan Paulo T Zaragoza, Regina A. Baglia, Maxime A. Siegler, David P. GoldbergAbstract:The oxygen atom transfer (OAT) reactivity of two Valence Tautomers of a MnV(O) porphyrinoid complex was compared. The OAT kinetics of MnV(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato3–) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV–vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 104 M–1 s–1. Characterization of the OAT transition state analogues MnIII(OPPh3)(TBP8Cz) and MnIII(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A Valence Tautomer of the closed-shell MnV(O)(TBP8Cz) can be stabilized by the addition of Lewis and Bronsted acids, resulting in the open-shell MnIV(O)(TBP8Cz•+):LA (LA = ZnII, B(C6F5)3, H+) complexes. These MnIV(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10–3 – 8.7 M–1 s–1), contrasting the previously observed rate increase of H-atom transfer (HAT) for MnIV(O)(TBP8Cz•+):LA ...
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Activation of a High-Valent Manganese–Oxo Complex by a Nonmetallic Lewis Acid
2015Co-Authors: Regina A. Baglia, Maximilian Dürr, Ivana Ivanović-burmazović, David P. GoldbergAbstract:The reaction of a manganese(V)–oxo porphyrinoid complex with the Lewis acid B(C6F5)3 leads to reversible stabilization of the Valence Tautomer MnIV(O)(π-radical cation). The latter complex, in combination with B(C6F5)3, reacts with ArO–H substrates via formal hydrogen-atom transfer and exhibits dramatically increased reaction rates over the MnV(O) starting material
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Strong Inhibition of O‑Atom Transfer Reactivity for MnIV(O)(π-Radical-Cation)(Lewis Acid) versus MnV(O) Porphyrinoid Complexes
2015Co-Authors: Jan Paulo T. Zaragoza, Regina A. Baglia, Maxime A. Siegler, David P. GoldbergAbstract:The oxygen atom transfer (OAT) reactivity of two Valence Tautomers of a MnV(O) porphyrinoid complex was compared. The OAT kinetics of MnV(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato3–) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV–vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 104 M–1 s–1. Characterization of the OAT transition state analogues MnIII(OPPh3)(TBP8Cz) and MnIII(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A Valence Tautomer of the closed-shell MnV(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell MnIV(O)(TBP8Cz•+):LA (LA = ZnII, B(C6F5)3, H+) complexes. These MnIV(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10–3 – 8.7 M–1 s–1), contrasting the previously observed rate increase of H-atom transfer (HAT) for MnIV(O)(TBP8Cz•+):LA with phenols. A Hammett analysis showed that the OAT reactivity for MnIV(O)(TBP8Cz•+):LA is influenced by the Lewis acid strength. Spectral redox titration of MnIV(O)(TBP8Cz•+):ZnII gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its Valence Tautomer MnV(O)(TBP8Cz) (Ered = −0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) Valence Tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of Valence Tautomers such as MV(O)(porph) versus MIV(O)(porph•+) (M = Mn or Fe) found in heme enzymes
Winnie H Liang - One of the best experts on this subject based on the ideXlab platform.
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charge and spin state characterization of cobalt bis o dioxolene Valence Tautomers using co kβ x ray emission and l edge x ray absorption spectroscopies
Inorganic Chemistry, 2017Co-Authors: Winnie H Liang, Thomas Kroll, Dennis Nordlund, Tsuchien Weng, Dimosthenis Sokaras, Cortlandt G Pierpont, Kelly J GaffneyAbstract:The Valence Tautomeric states of Co(phen)(3,5-DBQ)2 and Co(tmeda)(3,5-DBQ)2, where 3,5-DBQ is either the semiquinone (SQ–) or catecholate (Cat2–) form of 3,5-di-tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of Valence Tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature Valence Tautomer can be described as a low-spin CoIII configuration and the high-temperature Valence Tautomer as a high-spin CoII configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature Valence Tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. Th...
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Charge and Spin-State Characterization of Cobalt Bis(o‑dioxolene) Valence Tautomers Using Co Kβ X‑ray Emission and L‑Edge X‑ray Absorption Spectroscopies
2016Co-Authors: Winnie H Liang, Thomas Kroll, Dennis Nordlund, Tsuchien Weng, Dimosthenis Sokaras, Cortlandt G Pierpont, Kelly J GaffneyAbstract:The Valence Tautomeric states of Co(phen)(3,5-DBQ)2 and Co(tmeda)(3,5-DBQ)2, where 3,5-DBQ is either the semiquinone (SQ–) or catecholate (Cat2–) form of 3,5-di-tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of Valence Tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature Valence Tautomer can be described as a low-spin CoIII configuration and the high-temperature Valence Tautomer as a high-spin CoII configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature Valence Tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. The nature and strength of the magnetic exchange interaction between the cobalt center and SQ– in cobalt Valence Tautomers is discussed in view of the effective spin at the Co site from Kβ XES and the molecular spin moment from magnetic susceptibility measurements
Mahdi M Abuomar - One of the best experts on this subject based on the ideXlab platform.
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Valence Tautomerization of high valent manganese v oxo corrole induced by protonation of the oxo ligand
Journal of the American Chemical Society, 2015Co-Authors: Curt J Bougher, Shuo Liu, Scott D Hicks, Mahdi M AbuomarAbstract:The addition of an organic acid to the manganese(V)-oxo corrole complex (tpfc)Mn(V)(O) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole) induces Valence Tautomerization resulting in the formation of (tpfc(+•))Mn(IV)(OH) in acetonitrile at 298 K. The corrole radical cation manganese(IV) hydroxo complex has been fully characterized by EPR, (1)H NMR, and UV-vis spectroscopy. The reactivity of the Valence Tautomer (tpfc(+•))Mn(IV)(OH) is compared to that of (tpfc)Mn(V)(O) in three reaction types: hydrogen atom transfer (HAT), electron transfer (ET), and oxygen atom transfer (OAT). (tpfc(+•))Mn(IV)(OH) shows a dramatic 5 orders of magnitude enhancement in the rate of ET but surprisingly does not undergo OAT with PhSMe. The high-valent (tpfc)Mn(V)(O) complex is moderately more reactive toward HAT with substituted phenol and shows superior activity in OAT.
