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Cai YB, Yao SY, Hu M, Liu X, Zhang JL. Manganese protoporphyrin IX reconstituted myoglobin capable of epoxidation of the CC bond with Oxone®. Inorg Chem Front 2016. [DOI: 10.1039/c6qi00120c] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Myoglobin with three distal histidines stabilizes KHSO5, facilitates the O–O bond heterocleavage, and firstly catalyzes epoxidation with the MnPPIX cofactor.
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Affiliation(s)
- Yuan-Bo Cai
- Beijing National Laboratory for Molecular Sciences
- State Key Laboratory of Rare Earth Materials Chemistry and Applications
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
| | - Si-Yu Yao
- Beijing National Laboratory for Molecular Sciences
- State Key Laboratory of Rare Earth Materials Chemistry and Applications
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
| | - Mo Hu
- Institute of Analytical Chemistry and Synthetic and Functional Biomolecules Center
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
- P. R. China
| | - Xiaoyun Liu
- Institute of Analytical Chemistry and Synthetic and Functional Biomolecules Center
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
- P. R. China
| | - Jun-Long Zhang
- Beijing National Laboratory for Molecular Sciences
- State Key Laboratory of Rare Earth Materials Chemistry and Applications
- College of Chemistry and Molecular Engineering
- Peking University
- Beijing 100871
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52
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Wu X, Yang X, Lee YM, Nam W, Sun L. A nonheme manganese(IV)-oxo species generated in photocatalytic reaction using water as an oxygen source. Chem Commun (Camb) 2015; 51:4013-6. [PMID: 25658677 DOI: 10.1039/c4cc10411k] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A nonheme manganese(IV)-oxo complex, [Mn(IV)(O)(BQCN)](2+), was generated in the photochemical and chemical oxidation of [Mn(II)(BQCN)](2+) with water as an oxygen source, respectively. The photocatalytic oxidation of organic substrates, such as alcohol and sulfide, by [Mn(II)(BQCN)](2+) has been demonstrated in both neutral and acidic media.
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Affiliation(s)
- Xiujuan Wu
- State Key Laboratory of Fine Chemicals, Dalian University of Technology (DUT), DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian 116024, China.
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53
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Neu HM, Baglia RA, Goldberg DP. A Balancing Act: Stability versus Reactivity of Mn(O) Complexes. Acc Chem Res 2015; 48:2754-64. [PMID: 26352344 DOI: 10.1021/acs.accounts.5b00273] [Citation(s) in RCA: 99] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A large class of heme and non-heme metalloenzymes utilize O2 or its derivatives (e.g., H2O2) to generate high-valent metal-oxo intermediates for performing challenging and selective oxidations. Due to their reactive nature, these intermediates are often short-lived and very difficult to characterize. Synthetic chemists have sought to prepare analogous metal-oxo complexes with ligands that impart enough stability to allow for their characterization and an examination of their inherent reactivity. The challenge in designing these molecules is to achieve a balance between their stability, which should allow for their in situ characterization or isolation, and their reactivity, in which they can still participate in interesting chemical transformations. This Account focuses on our recent efforts to generate and stabilize high-valent manganese-oxo porphyrinoid complexes and tune their reactivity in the oxidation of organic substrates. Dioxygen can be used to generate a high-valent Mn(V)(O) corrolazine (Mn(V)(O)(TBP8Cz)) by irradiation of Mn(III)(TBP8Cz) with visible light in the presence of a C-H substrate. Quantitative formation of the Mn(V)(O) complex occurs with concomitant selective hydroxylation of the benzylic substrate hexamethylbenzene. Addition of a strong H(+) donor converted this light/O2/substrate reaction from a stoichiometric to a catalytic process with modest turnovers. The addition of H(+) likely activates a transient Mn(V)(O) complex to achieve turnover, whereas in the absence of H(+), the Mn(V)(O) complex is an unreactive "dead-end" complex. Addition of anionic donors to the Mn(V)(O) complex also leads to enhanced reactivity, with a large increase in the rate of two-electron oxygen atom transfer (OAT) to thioether substrates. Spectroscopic characterization (Mn K-edge X-ray absorption and resonance Raman spectroscopies) revealed that the anionic donors (X(-)) bind to the Mn(V) ion to form six-coordinate [Mn(V)(O)(X)](-) complexes. An unusual "V-shaped" Hammett plot for the oxidation of para-substituted thioanisole derivatives suggested that six-coordinate [Mn(V)(O)(X)](-) complexes can act as both electrophiles and nucleophiles, depending on the nature of the substrate. Oxidation of the Mn(V)(O) corrolazine resulted in the in situ generation of a Mn(V)(O) π-radical cation complex, [Mn(V)(O)(TBP8Cz(•+))](+), which exhibited more than a 100-fold rate increase in the oxidation of thioethers. The addition of Lewis acids (LA; Zn(II), B(C6F5)3) to the closed-shell, diamagnetic Mn(V)(O)(TBP8Cz) stabilized a paramagnetic valence tautomer Mn(IV)(O)(TBP8Cz(•+))(LA), which was characterized as a second π-radical cation complex by NMR, EPR, UV-vis, and high resolution cold spray ionization MS. The Mn(IV)(O)(TBP8Cz(•+))(LA) complexes are able to abstract H(•) from phenols and exhibit a rate enhancement of up to ∼100-fold over the parent Mn(V)(O) valence tautomer. In contrast, a large decrease in rate is observed for OAT for the Mn(IV)(O)(TBP8Cz(•+))(LA) complexes. The rate enhancement for hydrogen atom transfer (HAT) may derive from the higher redox potential for the π-radical cation complex, while the large rate decrease seen for OAT may come from a decrease in electrophilicity for an Mn(IV)(O) versus Mn(V)(O) complex.
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Affiliation(s)
- Heather M. Neu
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Regina A. Baglia
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David P. Goldberg
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
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54
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Kalutharage N, Yi CS. Scope and Mechanistic Analysis for Chemoselective Hydrogenolysis of Carbonyl Compounds Catalyzed by a Cationic Ruthenium Hydride Complex with a Tunable Phenol Ligand. J Am Chem Soc 2015; 137:11105-14. [DOI: 10.1021/jacs.5b06097] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Nishantha Kalutharage
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881, United States
| | - Chae S. Yi
- Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881, United States
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55
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Schreiber RE, Cohen H, Leitus G, Wolf SG, Zhou A, Que L, Neumann R. Reactivity and O2 Formation by Mn(IV)- and Mn(V)-Hydroxo Species Stabilized within a Polyfluoroxometalate Framework. J Am Chem Soc 2015; 137:8738-48. [PMID: 26070034 PMCID: PMC4939246 DOI: 10.1021/jacs.5b03456] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Manganese(IV,V)-hydroxo and oxo complexes are often implicated in both catalytic oxygenation and water oxidation reactions. Much of the research in this area is designed to structurally and/or functionally mimic enzymes. On the other hand, the tendency of such mimics to decompose under strong oxidizing conditions makes the use of molecular inorganic oxide clusters an enticing alternative for practical applications. In this context it is important to understand the reactivity of conceivable reactive intermediates in such an oxide-based chemical environment. Herein, a polyfluoroxometalate (PFOM) monosubstituted with manganese, [NaH2(Mn-L)W17F6O55](q-), has allowed the isolation of a series of compounds, Mn(II, III, IV and V), within the PFOM framework. Magnetic susceptibility measurements show that all the compounds are high spin. XPS and XANES measurements confirmed the assigned oxidation states. EXAFS measurements indicate that Mn(II)PFOM and Mn(III)PFOM have terminal aqua ligands and Mn(V)PFOM has a terminal hydroxo ligand. The data are more ambiguous for Mn(IV)PFOM where both terminal aqua and hydroxo ligands can be rationalized, but the reactivity observed more likely supports a formulation of Mn(IV)PFOM as having a terminal hydroxo ligand. Reactivity studies in water showed unexpectedly that both Mn(IV)-OH-PFOM and Mn(V)-OH-PFOM are very poor oxygen-atom donors; however, both are highly reactive in electron transfer oxidations such as the oxidation of 3-mercaptopropionic acid to the corresponding disulfide. The Mn(IV)-OH-PFOM compound reacted in water to form O2, while Mn(V)-OH-PFOM was surprisingly indefinitely stable. It was observed that addition of alkali cations (K(+), Rb(+), and Cs(+)) led to the aggregation of Mn(IV)-OH-PFOM as analyzed by electron microscopy and DOSY NMR, while addition of Li(+) and Na(+) did not lead to aggregates. Aggregation leads to a lowering of the entropic barrier of the reaction without changing the free energy barrier. The observation that O2 formation is fastest in the presence of Cs(+) and ∼fourth order in Mn(IV)-OH-PFOM supports a notion of a tetramolecular Mn(IV)-hydroxo intermediate that is viable for O2 formation in an oxide-based chemical environment. A bimolecular reaction mechanism involving a Mn(IV)-hydroxo based intermediate appears to be slower for O2 formation.
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Affiliation(s)
- Roy E. Schreiber
- Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Hagai Cohen
- Department for Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Gregory Leitus
- Department for Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Sharon G. Wolf
- Department for Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Ang Zhou
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Ronny Neumann
- Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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56
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Chantarojsiri T, Sun Y, Long JR, Chang CJ. Water-Soluble Iron(IV)-Oxo Complexes Supported by Pentapyridine Ligands: Axial Ligand Effects on Hydrogen Atom and Oxygen Atom Transfer Reactivity. Inorg Chem 2015; 54:5879-87. [PMID: 26039655 DOI: 10.1021/acs.inorgchem.5b00658] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report the photochemical generation and study of a family of water-soluble iron(IV)-oxo complexes supported by pentapyridine PY5Me2-X ligands (PY5Me2 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine; X = CF3, H, Me, or NMe2), in which the oxidative reactivity of these ferryl species correlates with the electronic properties of the axial pyridine ligand. Synthesis of a systematic series of [Fe(II)(L)(PY5Me2-X)](2+) complexes, where L = CH3CN or H2O, and characterizations by several methods, including X-ray crystallography, cyclic voltammetry, and Mössbauer spectroscopy, show that increasing the electron-donating ability of the axial pyridine ligand tracks with less positive Fe(III)/Fe(II) reduction potentials and quadrupole splitting parameters. The Fe(II) precursors are readily oxidized to their Fe(IV)-oxo counterparts using either chemical outer-sphere oxidants such as CAN (ceric ammonium nitrate) or flash-quench photochemical oxidation with [Ru(bpy)3](2+) as a photosensitizer and K2S2O8 as a quencher. The Fe(IV)-oxo complexes are capable of oxidizing the C-H bonds of alkane (4-ethylbenzenesulfonate) and alcohol (benzyl alcohol) substrates via hydrogen atom transfer (HAT) and an olefin (4-styrenesulfonate) substrate by oxygen atom transfer (OAT). The [Fe(IV)(O)(PY5Me2-X)](2+) derivatives with electron-poor axial ligands show faster rates of HAT and OAT compared to their counterparts supported by electron-rich axial donors, but the magnitudes of these differences are relatively modest.
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Affiliation(s)
| | - Yujie Sun
- #Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
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57
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Zaragoza JPT, Baglia RA, Siegler MA, Goldberg DP. Strong Inhibition of O-Atom Transfer Reactivity for Mn(IV)(O)(π-Radical-Cation)(Lewis Acid) versus Mn(V)(O) Porphyrinoid Complexes. J Am Chem Soc 2015; 137:6531-40. [PMID: 25964988 DOI: 10.1021/jacs.5b00875] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The oxygen atom transfer (OAT) reactivity of two valence tautomers of a Mn(V)(O) porphyrinoid complex was compared. The OAT kinetics of Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)) 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) × 10(4) M(-1) s(-1). Characterization of the OAT transition state analogues Mn(III)(OPPh3)(TBP8Cz) and Mn(III)(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A valence tautomer of the closed-shell Mn(V)(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell Mn(IV)(O)(TBP8Cz(•+)):LA (LA = Zn(II), B(C6F5)3, H(+)) complexes. These Mn(IV)(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 Mn(IV)(O)(TBP8Cz(•+)):LA with phenols. A Hammett analysis showed that the OAT reactivity for Mn(IV)(O)(TBP8Cz(•+)):LA is influenced by the Lewis acid strength. Spectral redox titration of Mn(IV)(O)(TBP8Cz(•+)):Zn(II) gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its valence tautomer Mn(V)(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 M(V)(O)(porph) versus M(IV)(O)(porph(•+)) (M = Mn or Fe) found in heme enzymes.
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Affiliation(s)
- Jan Paulo T Zaragoza
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Regina A Baglia
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Maxime A Siegler
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - David P Goldberg
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
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58
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Neu HM, Jung J, Baglia RA, Siegler MA, Ohkubo K, Fukuzumi S, Goldberg DP. Light-driven, proton-controlled, catalytic aerobic C-H oxidation mediated by a Mn(III) porphyrinoid complex. J Am Chem Soc 2015; 137:4614-7. [PMID: 25839905 DOI: 10.1021/jacs.5b00816] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The visible light-driven, catalytic aerobic oxidation of benzylic C-H bonds was mediated by a Mn(III) corrolazine complex. To achieve catalytic turnovers, a strict selective requirement for the addition of protons was established. The resting state of the catalyst was unambiguously characterized by X-ray diffraction as [Mn(III)(H2O)(TBP8Cz(H))](+), in which a single, remote site on the ligand is protonated. If two remote sites are protonated, however, reactivity with O2 is shut down. Spectroscopic methods revealed that the related Mn(V)(O) complex is also protonated at the same remote site at -60 °C, but undergoes valence tautomerization upon warming.
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Affiliation(s)
- Heather M Neu
- †Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Jieun Jung
- ‡Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency, Suita, Osaka 565-0871, Japan
| | - Regina A Baglia
- †Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Maxime A Siegler
- †Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kei Ohkubo
- ‡Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency, Suita, Osaka 565-0871, Japan
| | - Shunichi Fukuzumi
- ‡Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, Japan Science and Technology Agency, Suita, Osaka 565-0871, Japan.,§Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, Korea
| | - David P Goldberg
- †Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
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Barman P, Vardhaman AK, Martin B, Wörner SJ, Sastri CV, Comba P. Influence of ligand architecture on oxidation reactions by high-valent nonheme manganese oxo complexes using water as a source of oxygen. Angew Chem Int Ed Engl 2014; 54:2095-9. [PMID: 25557423 DOI: 10.1002/anie.201409476] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Revised: 11/17/2014] [Indexed: 11/07/2022]
Abstract
Mononuclear nonheme Mn(IV)=O complexes with two isomers of a bispidine ligand have been synthesized and characterized by various spectroscopies and density functional theory (DFT). The Mn(IV)=O complexes show reactivity in oxidation reactions (hydrogen-atom abstraction and sulfoxidation). Interestingly, one of the isomers (L(1) ) is significantly more reactive than the other (L(2) ), while in the corresponding Fe(IV)=O based oxidation reactions the L(2) -based system was previously found to be more reactive than the L(1) -based catalyst. This inversion of reactivities is discussed on the basis of DFT and molecular mechanics (MM) model calculations, which indicate that the order of reactivities are primarily due to a switch of reaction channels (σ versus π) and concomitant steric effects.
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Affiliation(s)
- Prasenjit Barman
- Department of Chemistry, Indian Institute of Technology Guwahati, Assam, 781039 (India)
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60
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Barman P, Vardhaman AK, Martin B, Wörner SJ, Sastri CV, Comba P. Influence of Ligand Architecture on Oxidation Reactions by High-Valent Nonheme Manganese Oxo Complexes Using Water as a Source of Oxygen. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201409476] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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