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El-Ghamry HA, Gaber M, Alkhatib FM, Al Shareef HF, Takroni KM, Fathalla SK. Insight into the synthesis, structure affirmation and catalytic efficiency of divalent and trivalent metal chelates of mandelic acid hydrazone derivative. RSC Adv 2024; 14:30673-30686. [PMID: 39324037 PMCID: PMC11423900 DOI: 10.1039/d4ra05769d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2024] [Accepted: 09/18/2024] [Indexed: 09/27/2024] Open
Abstract
The current work reports the synthesis of Cr(iii), Mn(ii), Co(ii), Ni(ii) and Cu(ii) chelates of the Schiff base ligand named hydroxy-phenyl-acetic acid (2-hydroxy-naphthalen-1-ylmethylene)-hydrazide with multi-chelation centre toward metal ions. The spectral tools, 1H-NMR, FTIR, mass, UV-vis spectra, and the analytical elemental and thermal analysis, in addition to magnetic moment and conductivity measurements all combined have been applied to conclude the structure and geometry of the synthesized metal complexes. The formed metal chelates have been assured to be formed with the molar compositions of 1 L : 1 M for PANH-Cr, PANH-Mn, PANH-Co, PANH-Ni and 2 L : 1 M for PANH-Cu. All the complexes have been confirmed to be non-electrolytic except the PANH-Mn and PANH-Ni which are 1 : 1 electrolytes. FTIR spectral analysis assured the ligand to act as mono basic bi or tridentate ligand leading to the formation of octahedral complexes with all metals except Cu(ii) complex which assured to has square planar structure. Except PANH-Cr, all the synthesized metal chelates exhibited phenoxazinone synthase like efficacy with varying activity with dramatically high activity for PANH-Mn complex with TOF number of 169.89 h-1.
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Affiliation(s)
- Hoda A El-Ghamry
- Chemistry Department, Faculty of Science, Tanta University Tanta Egypt
| | - Mohamed Gaber
- Chemistry Department, Faculty of Science, Tanta University Tanta Egypt
| | - Fatmah M Alkhatib
- Chemistry Department, Faculty of Applied Science, Umm Al-Qura University Makkah Saudi Arabia
| | - Hossa F Al Shareef
- Chemistry Department, Faculty of Applied Science, Umm Al-Qura University Makkah Saudi Arabia
| | - Khadiga M Takroni
- Chemistry Department, Faculty of Applied Science, Umm Al-Qura University Makkah Saudi Arabia
| | - Shaimaa K Fathalla
- Chemistry Department, Faculty of Science, Taif University Taif Saudi Arabia
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2
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Gupta S, Arora P, Kumar R, Awasthi A, Chandra B, Eerlapally R, Xiong J, Guo Y, Que L, Draksharapu A. Formation of a Reactive [Mn(III)-O-Ce(IV)] Species and its Facile Equilibrium with Related Mn(IV)(OX) (X = Sc or H) Complexes. Angew Chem Int Ed Engl 2024; 63:e202316378. [PMID: 37997195 PMCID: PMC10873046 DOI: 10.1002/anie.202316378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 11/22/2023] [Accepted: 11/23/2023] [Indexed: 11/25/2023]
Abstract
Lewis acid-bound high valent Mn-oxo species are of great importance due to their relevance to photosystem II. Here, we report the synthesis of a unique [(BnTPEN)Mn(III)-O-Ce(IV)(NO3 )4 ]+ adduct (2) by the reaction of (BnTPEN)Mn(II) (1) with 4 eq. ceric ammonium nitrate. 2 has been characterized using UV/Vis, NMR, resonance Raman spectroscopy, as well as by mass spectrometry. Treatment of 2 with Sc(III)(OTf)3 results in the formation of (BnTPEN)Mn(IV)-O-Sc(III) (3), while HClO4 addition to 2 forms (BnTPEN)Mn(IV)-OH (4), reverting to 2 upon Ce(III)(NO3 )3 addition. 2 can also be prepared by the oxidation of 1 eq. Ce(III)(NO3 )3 with [(BnTPEN)Mn(IV)=O]2+ (5). In addition, the EPR spectroscopy revealed the elegant temperature-dependent equilibria between 2 and Mn(IV) species. The binding of redox-active Ce(IV) boosts electron transfer efficiency of 2 towards ferrocenes. Remarkably, the newly characterized Mn(III)-O-Ce(IV) species can carry out O-atom and H-atom transfer reactions.
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Affiliation(s)
- Sikha Gupta
- Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Pragya Arora
- Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Rakesh Kumar
- Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Ayushi Awasthi
- Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Bittu Chandra
- Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA
| | - Raju Eerlapally
- Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Jin Xiong
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Lawrence Que
- Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA
| | - Apparao Draksharapu
- Southern Laboratories-208A, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
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3
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Arora P, Gupta S, Kumari Vechalapu S, Kumar R, Awasthi A, Senthil S, Khanna S, Allimuthu D, Draksharapu A. Mn(II) Polypyridyl Complexes: Precursors to High Valent Mn(V)=O Species and Inhibitors of Cancer Cell Proliferation. Chemistry 2023; 29:e202301506. [PMID: 37415318 DOI: 10.1002/chem.202301506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 06/27/2023] [Accepted: 07/06/2023] [Indexed: 07/08/2023]
Abstract
The reaction of [(L)MnII ]2+ (L = neutral polypyridine ligand framework) in the presence of mCPBA (mCPBA = m-Chloroperoxybenzoic acid) generates a putative MnV =O species at RT. The proposed MnV =O species is capable of performing the aromatic hydroxylation of Cl-benzoic acid derived from mCPBA to give [(L)MnIII (m-Cl-salicylate)]+ , which in the presence of excess mCPBA generates a metastable [(L)MnV (O)(m-Cl-salicylate)]+ , characterized by UV/Vis absorption, EPR, resonance Raman spectroscopy, and ESI-MS studies. The current study highlights the fact that [(L)MnIII (m-Cl-salicylate)]+ formation may not be a dead end for catalysis. Further, a plausible mechanism has been proposed for the formation of [(L)MnV (O)-m-Cl-salicylate)]+ from [(L)MnIII (m-Cl-salicylate)]+ . The characterized transient [(L)MnV (O)-m-Cl-salicylate)]+ reported in the current work exhibits high reactivity for oxygen atom transfer reactions, supported by the electrophilic character depicted from Hammett studies using a series of para-substituted thioanisoles. The unprecedented study starting from a non-heme neutral polypyridine ligand framework paves a path for mimicking the natural active site of photosystem II under ambient conditions. Finally, evaluating the intracellular effect of Mn(II) complexes revealed an enhanced intracellular ROS and mitochondrial dysfunction to prevent the proliferation of hepatocellular carcinoma and breast cancer cells.
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Affiliation(s)
- Pragya Arora
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Sikha Gupta
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Sai Kumari Vechalapu
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Rakesh Kumar
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Ayushi Awasthi
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Sathyapriya Senthil
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Shweta Khanna
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Dharmaraja Allimuthu
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
| | - Apparao Draksharapu
- Southern Laboratories, Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
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4
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Shiau AA, Lee HB, Oyala PH, Agapie T. Coordination Number in High-Spin-Low-Spin Equilibrium in Cluster Models of the S 2 State of the Oxygen Evolving Complex. J Am Chem Soc 2023; 145:14592-14598. [PMID: 37366634 PMCID: PMC10575483 DOI: 10.1021/jacs.3c04464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
The S2 state of the Oxygen Evolving Complex (OEC) of Photosystem II (PSII) shows high-spin (HS) and low-spin (LS) EPR signals attributed to distinct structures based on computation. Five-coordinate MnIII centers are proposed in these species but are absent in available spectroscopic model complexes. Herein, we report the synthesis, crystal structure, electrochemistry, SQUID magnetometry, and EPR spectroscopy of a MnIIIMnIV3O4 cuboidal complex featuring five-coordinate MnIII. This cluster displays a spin ground state of S = 5/2, while conversion to a six-coordinate Mn upon treatment with water results in a spin state change to S = 1/2. These results demonstrate that coordination number, without dramatic changes within the Mn4O4 core, has a substantial effect on spectroscopy.
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Affiliation(s)
- Angela A Shiau
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd MC 127-72, Pasadena, California 91125, United States
| | - Heui Beom Lee
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd MC 127-72, Pasadena, California 91125, United States
| | - Paul H Oyala
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd MC 127-72, Pasadena, California 91125, United States
| | - Theodor Agapie
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd MC 127-72, Pasadena, California 91125, United States
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5
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Shiau AA, Lee HB, Oyala PH, Agapie T. Mn IV4O 4 Model of the S 3 Intermediate of the Oxygen-Evolving Complex: Effect of the Dianionic Disiloxide Ligand. Inorg Chem 2023; 62:1791-1796. [PMID: 35829634 DOI: 10.1021/acs.inorgchem.2c01612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Synthetic complexes provide useful models to study the interplay between the structure and spectroscopy of the different Sn-state intermediates of the oxygen-evolving complex (OEC) of photosystem II (PSII). Complexes containing the MnIV4 core corresponding to the S3 state, the last observable intermediate prior to dioxygen formation, remain very rare. Toward the development of synthetic strategies to stabilize highly oxidized tetranuclear complexes, ligands with increased anion charge were pursued. Herein, we report the synthesis, electrochemistry, SQUID magnetometry, and electron paramagnetic resonance spectroscopy of a stable MnIV4O4 cuboidal complex supported by a disiloxide ligand. The substitution of an anionic acetate or amidate ligand with a dianionic disiloxide ligand shifts the reduction potential of the MnIIIMnIV3/MnIV4 redox couple by up to ∼760 mV, improving stability. The S = 3 spin ground state of the siloxide-ligated MnIV4O4 complex matches the acetate and amidate variants, in corroboration with the MnIV4 assignment of the S3 state of the OEC.
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Affiliation(s)
- Angela A Shiau
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
| | - Heui Beom Lee
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
| | - Paul H Oyala
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
| | - Theodor Agapie
- Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
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6
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Bigness A, Vaddypally S, Zdilla MJ, Mendoza-Cortes JL. Ubiquity of cubanes in bioinorganic relevant compounds. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2021.214168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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8
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Reed CJ, Agapie T. A Terminal Fe III-Oxo in a Tetranuclear Cluster: Effects of Distal Metal Centers on Structure and Reactivity. J Am Chem Soc 2019; 141:9479-9484. [PMID: 31083986 DOI: 10.1021/jacs.9b03157] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Tetranuclear Fe clusters have been synthesized bearing a terminal FeIII-oxo center stabilized by hydrogen-bonding interactions from pendant ( tert-butylamino)pyrazolate ligands. This motif was supported in multiple Fe oxidation states, ranging from [FeII2FeIII2] to [FeIII4]; two oxidation states were structurally characterized by single-crystal X-ray diffraction. The reactivity of the FeIII-oxo center in proton-coupled electron transfer with X-H (X = C, O) bonds of various strengths was studied in conjunction with analysis of thermodynamic square schemes of the cluster oxidation states. These results demonstrate the important role of distal metal centers in modulating the reactivity of a terminal metal-oxo.
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Affiliation(s)
- Christopher J Reed
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
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9
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Lee HB, Agapie T. Redox Tuning via Ligand-Induced Geometric Distortions at a YMn 3O 4 Cubane Model of the Biological Oxygen Evolving Complex. Inorg Chem 2019; 58:14998-15003. [PMID: 31095368 PMCID: PMC6876925 DOI: 10.1021/acs.inorgchem.9b00510] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
![]()
The function of proteins
involved in electron transfer is dependent
on cofactors attaining the necessary reduction potentials. We establish
a mode of cluster redox tuning through steric pressure on a synthetic
model related to Photosystem II. Resembling the cuboidal [CaMn3O4] subsite of the biological oxygen evolving complex
(OEC), [Mn4O4] and [YMn3O4] complexes featuring ligands of different basicity and chelating
properties were characterized by cyclic voltammetry. In the absence
of ligand-induced distortions, increasing the basicity of the ligands
results in a decrease of cluster reduction potential. Contraction
of Y-oxo/Y–Mn distances by 0.1/0.15 Å enforced by a chelating
ligand results in an increase of cluster reduction potential even
in the presence of strongly basic donors. Related protein-induced
changes in Ca-oxo/Ca–Mn distances may have similar effects
in tuning the redox potential of the OEC through entatic states and
may explain the cation size dependence on the progression of the S-state
cycle. The redox properties of [YMn3O4] and
[Mn4O4] complexes featuring bridging ligands
of different basicity and chelating properties are reported. In the
absence of ligand-induced geometric distortions, increasing the basicity
of the ligands results in a decrease of cluster reduction potential.
A chelating ligand results in contractions of Y-oxo distances by ∼0.1
Å, which correlates with an increase of cluster reduction potential
even in the presence of strongly basic donors.
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Affiliation(s)
- Heui Beom Lee
- Department of Chemistry and Chemical Engineering , California Institute of Technology , 1200 E. California Blvd MC 127-72 , Pasadena , California 91125 , United States
| | - Theodor Agapie
- Department of Chemistry and Chemical Engineering , California Institute of Technology , 1200 E. California Blvd MC 127-72 , Pasadena , California 91125 , United States
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10
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Das A, Chakraborty M, Maity S, Ghosh A. The catalytic activities and magnetic behaviours of rare μ3-chlorido and μ1,1,1-azido bridged defective dicubane tetranuclear Mn(ii) complexes. Dalton Trans 2019; 48:9342-9356. [DOI: 10.1039/c9dt01567a] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A μ3-chlorido and a μ1,1,1-azido bridged defective dicubane tetranuclear Mn(ii) complexes of polynucleating Mannich base ligand show significant catalytic oxidase activities and are antiferromagnetically coupled which is rationalized by DFT calculations.
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Affiliation(s)
- Avijit Das
- Department of Chemistry
- University College of Science
- University of Calcutta
- Kolkata 700009
- India
| | - Maharudra Chakraborty
- Department of Chemistry
- University College of Science
- University of Calcutta
- Kolkata 700009
- India
| | - Souvik Maity
- Department of Chemistry
- University College of Science
- University of Calcutta
- Kolkata 700009
- India
| | - Ashutosh Ghosh
- Department of Chemistry
- University College of Science
- University of Calcutta
- Kolkata 700009
- India
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Zhang B, Sun L. Why nature chose the Mn 4CaO 5 cluster as water-splitting catalyst in photosystem II: a new hypothesis for the mechanism of O-O bond formation. Dalton Trans 2018; 47:14381-14387. [PMID: 30129959 DOI: 10.1039/c8dt01931b] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Resolving the questions, namely, the selection of Mn by nature to build the oxygen-evolving complex (OEC) and the presence of a cubic Mn3CaO4 structure in OEC coupled with an additional dangling Mn (Mn4) via μ-O atom are not only important to uncover the secret of water oxidation in nature, but also essential to achieve a blueprint for developing advanced water-oxidation catalysts for artificial photosynthesis. Based on the important experimental results reported so far in the literature and on our own findings, we propose a new hypothesis for the water oxidation mechanism in OEC. In this new hypothesis, we propose for the first time, a complete catalytic cycle involving a charge-rearrangement-induced MnVII-dioxo species on the dangling Mn4 during the S3 → S4 transition. Moreover, the O-O bond is formed within this MnVII-dioxo site, which is totally different from that discussed in other existing proposals.
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Affiliation(s)
- Biaobiao Zhang
- Department of Chemistry, KTH Royal Institute of Technology, 10044 Stockholm, Sweden.
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12
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Zhang B, Daniel Q, Fan L, Liu T, Meng Q, Sun L. Identifying Mn VII-oxo Species during Electrochemical Water Oxidation by Manganese Oxide. iScience 2018; 4:144-152. [PMID: 30240736 PMCID: PMC6147022 DOI: 10.1016/j.isci.2018.05.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Revised: 05/08/2018] [Accepted: 05/25/2018] [Indexed: 12/02/2022] Open
Abstract
Identifying surface active intermediate species is essential to reveal the catalytic mechanism of water oxidation by metal-oxides-based catalysts and to develop more efficient catalysts for oxygen-oxygen bond formation. Here we report, through electrochemical methods and ex situ infrared spectroscopy, the identification of a MnVII = O intermediate during catalytic water oxidation by a c-disordered δ-MnOx with an onset-potential-dependent reduction peak at 0.93 V and an infrared peak at 912 cm−1. This intermediate is proved to be highly reactive and much more oxidative than permanganate ion. Therefore, we propose a new catalytic mechanism for water oxidation catalyzed by Mn oxides, with involvement of the MnVII = O intermediate in a resting state and the MnIV−O−MnVII = O as a real active species for oxygen-oxygen bond formation. A reactive MnVII-oxo intermediate was identified during water oxidation by a MnOx The MnVII-oxo species was proved to be much more oxidative than permanganate ion The MnIV−O−MnVII = O moiety is a real highly active state for O–O bond formation A new mechanism for Mn oxide-catalyzed electrocatalytic water oxidation is proposed
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Affiliation(s)
- Biaobiao Zhang
- Department of Chemistry, KTH Royal Institute of Technology, Stockholm 10044, Sweden
| | - Quentin Daniel
- Department of Chemistry, KTH Royal Institute of Technology, Stockholm 10044, Sweden
| | - Lizhou Fan
- Department of Chemistry, KTH Royal Institute of Technology, Stockholm 10044, Sweden
| | - Tianqi Liu
- Department of Chemistry, KTH Royal Institute of Technology, Stockholm 10044, Sweden
| | - Qijun Meng
- Department of Chemistry, KTH Royal Institute of Technology, Stockholm 10044, Sweden
| | - Licheng Sun
- Department of Chemistry, KTH Royal Institute of Technology, Stockholm 10044, Sweden; State Key Laboratory of Fine Chemicals, Institute of Artificial Photosynthesis, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT), Dalian 116024, P. R. China.
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13
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Zaragoza JPT, Siegler MA, Goldberg DP. A Reactive Manganese(IV)-Hydroxide Complex: A Missing Intermediate in Hydrogen Atom Transfer by High-Valent Metal-Oxo Porphyrinoid Compounds. J Am Chem Soc 2018. [PMID: 29542921 DOI: 10.1021/jacs.8b00350] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High-valent metal-hydroxide species are invoked as critical intermediates in both catalytic, metal-mediated O2 activation (e.g., by Fe porphyrin in Cytochrome P450) and O2 production (e.g., by the Mn cluster in Photosystem II). However, well-characterized mononuclear MIV(OH) complexes remain a rarity. Herein we describe the synthesis of MnIV(OH)(ttppc) (3) (ttppc = tris(2,4,6-triphenylphenyl) corrole), which has been characterized by X-ray diffraction (XRD). The large steric encumbrance of the ttppc ligand allowed for isolation of 3. The complexes MnV(O)(ttppc) (4) and MnIII(H2O)(ttppc) (1·H2O) were also synthesized and structurally characterized, providing a series of Mn complexes related only by the transfer of hydrogen atoms. Both 3 and 4 abstract an H atom from the O-H bond of 2,4-di- tert-butylphenol (2,4-DTBP) to give a radical coupling product in good yield (3 = 90(2)%, 4 = 91(5)%). Complex 3 reacts with 2,4-DTBP with a rate constant of k2 = 2.73(12) × 104 M-1 s-1, which is ∼3 orders of magnitude larger than 4 ( k2 = 17.4(1) M-1 s-1). Reaction of 3 with a series of para-substituted 2,6-di- tert-butylphenol derivatives (4-X-2,6-DTBP; X = OMe, Me, tBu, H) gives rate constants in the range k2 = 510(10)-36(1.4) M-1 s-1 and led to Hammett and Marcus plot correlations. Together with kinetic isotope effect measurements, it is concluded that O-H cleavage occurs by a concerted H atom transfer (HAT) mechanism and that the MnIV(OH) complex is a much more powerful H atom abstractor than the higher-valent MnV(O) complex, or even some FeIV(O) complexes.
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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
| | - 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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14
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Carsch KM, de Ruiter G, Agapie T. Intramolecular C-H and C-F Bond Oxygenation by Site-Differentiated Tetranuclear Manganese Models of the OEC. Inorg Chem 2017; 56:9044-9054. [PMID: 28731687 PMCID: PMC5669799 DOI: 10.1021/acs.inorgchem.7b01022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The dangler manganese center in the oxygen-evolving complex (OEC) of photosystem II plays an important role in the oxidation of water to dioxygen. Inspired by the structure of the OEC, we synthesized a series of site-differentiated tetra-manganese clusters [LMn3(PhPz)3OMn][OTf]x (2: x = 2; 3: x = 1) that features an apical manganese ion-distinct from the others-that is appended to a trinuclear manganese core through an μ4-oxygen atom bridge. This cluster design was targeted to facilitate studies of high-valent Mn-oxo formation, which is a proposed step in the mechanism for water oxidation by the OEC. Terminal Mn-oxo species-supported by a multinuclear motif-were targeted by treating 2 and 3 with iodosobenzene. Akin to our previously reported iron complexes, intramolecular arene hydroxylation was observed to yield the C-H bond oxygenated complexes [LMn3(PhPz)2(OArPz)OMn][OTf]x (5: x = 2; 6: x = 1). The fluorinated series [LMn3(F2ArPz)3OMn][OTf]x (8: x = 2; 9: x = 1) was also synthesized to mitigate the observed intramolecular hydroxylation. Treatment of 8 and 9 with iodosobenzene results in intramolecular arene C-F bond oxygenation as judged by electrospray ionization mass spectrometry. The observed aromatic C-H and C-F hydroxylation is suggestive of a putative high-valent terminal metal-oxo species, and it is one of the very few examples capable of oxygenating C-F bonds.
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Affiliation(s)
- Kurtis M. Carsch
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
| | - Graham de Ruiter
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States
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