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Chen X, Zhou R, Du Y, She Y, Yang YF. Mechanistic Insights into Oxidation of Benzaldehyde by Co-Peroxo Complexes. J Org Chem 2024; 89:9019-9026. [PMID: 38831395 DOI: 10.1021/acs.joc.4c00992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2024]
Abstract
Transition metal-peroxide complexes play a crucial role as intermediates in oxidation reactions. To unravel the mechanism of benzaldehyde oxidation by the Co-peroxo complex, we conducted density functional theory (DFT) calculations. The identified competing mechanisms include nucleophilic attack and hydrogen atom transfer (HAT). The nucleophilic attack pathway involves Co-O cleavage and nucleophilic attack, leading to the formation of the benzoate product. And the HAT pathway comprises O-O cleavage and HAT, ultimately resulting in the benzoate product. DFT calculations revealed that the formation of the end-on Co-superoxo complex 2 through Co-O cleavage, starting from the side-on Co-peroxo complex 1, is much more favorable than the formation of the two-terminal oxyl-radical intermediate 3 through O-O cleavage. Compared with the nucleophilic attack of benzaldehyde by 2, the abstraction of a hydrogen atom from benzaldehyde by 3 requires higher energy. The nature of the nucleophilicity of 2 and 3 accounts for the reactivity of the reaction.
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Affiliation(s)
- Xiahe Chen
- State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Key Laboratory of Green Chemistry-Synthesis Technology of Zhejiang Province, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
| | - Rongrong Zhou
- State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Key Laboratory of Green Chemistry-Synthesis Technology of Zhejiang Province, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
| | - Yuxin Du
- State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Key Laboratory of Green Chemistry-Synthesis Technology of Zhejiang Province, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
| | - Yuanbin She
- State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Key Laboratory of Green Chemistry-Synthesis Technology of Zhejiang Province, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
| | - Yun-Fang Yang
- State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Key Laboratory of Green Chemistry-Synthesis Technology of Zhejiang Province, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
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2
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Mu G, Gaynor RB, McIntyre BN, Donnadieu B, Creutz SE. Synthesis and Characterization of Bipyridyl-(Imidazole) n Mn(II) Compounds and Their Evaluation as Potential Precatalysts for Water Oxidation. Molecules 2023; 28:7221. [PMID: 37894706 PMCID: PMC10608871 DOI: 10.3390/molecules28207221] [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: 09/29/2023] [Revised: 10/20/2023] [Accepted: 10/21/2023] [Indexed: 10/29/2023] Open
Abstract
Metalloenzymes make extensive use of manganese centers for oxidative catalysis, including water oxidation; the need to develop improved synthetic catalysts for these processes has long motivated the development of bioinspired manganese complexes. Herein, we report a series of bpy-(imidazole)n (n = 1 or 2) (bpy = 2,2'-bipyridyl) ligands and their Mn2+ complexes. Four Mn2+ complexes are structurally characterized using single-crystal X-ray diffraction, revealing different tridentate and tetradentate ligand coordination modes. Cyclic voltammetry of the complexes is consistent with ligand-centered reductions and metal-centered oxidations, and UV-vis spectroscopy complemented by TD-DFT calculations shows primarily ligand-centered transitions with minor contributions from charge-transfer type transitions at higher energies. In solution, ESI-MS studies provide evidence for ligand reorganization, suggesting complex speciation behavior. The oxidation of the complexes in the presence of water is probed using cyclic voltammetry, but the low stability of the complexes in aqueous solution leads to decomposition and precludes their ultimate application as aqueous electrocatalysts. Possible reasons for the low stability and suggestions for improvement are discussed.
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Affiliation(s)
| | | | | | | | - Sidney E. Creutz
- Department of Chemistry, Mississippi State University, Mississippi State, Starkville, MS 39762, USA; (G.M.); (R.B.G.); (B.N.M.); (B.D.)
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3
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Grotemeyer EN, Parham JD, Jackson TA. Reaction landscape of a mononuclear Mn III-hydroxo complex with hydrogen peroxide. Dalton Trans 2023; 52:14350-14370. [PMID: 37767937 DOI: 10.1039/d3dt02672h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/29/2023]
Abstract
Peroxomanganese species have been proposed as key intermediates in the catalytic cycles of both manganese enzymes and synthetic catalysts. However, many of these intermediates have yet to be observed. Here, we report the formation of a series of intermediates, each generated from the reaction of the mononuclear MnIII-hydroxo complex [MnIII(OH)(dpaq2Me)]+ with hydrogen peroxide under slightly different conditions. By changing the acidity of the reaction mixture and/or the quantity of hydrogen peroxide added, we are able to control which intermediate forms. Using a combination of electronic absorption, 1H NMR, EPR, and X-ray absorption spectroscopies, as well as density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations, we formulate these intermediates as the bis(μ-oxo)dimanganese(III,IV) complex [MnIIIMnIV(μ-O)2(dpaq2Me)2]+, the MnIII-hydroperoxo complex [MnIII(OOH)(dpaq2Me)]+, and the MnIII-peroxo complex [MnIII(O2)(dpaq2Me)]. The formation of the MnIII-hydroperoxo species from the reaction of a MnIII-hydroxo complex with hydrogen peroxide mimics an elementary reaction proposed for many synthetic manganese catalysts that activate hydrogen peroxide.
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Affiliation(s)
- Elizabeth N Grotemeyer
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, KS 66045, USA.
| | - Joshua D Parham
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, KS 66045, USA.
| | - Timothy A Jackson
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, KS 66045, USA.
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4
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Jeong D, Selverstone Valentine J, Cho J. Bio-inspired mononuclear nonheme metal peroxo complexes: Synthesis, structures and mechanistic studies toward understanding enzymatic reactions. Coord Chem Rev 2023. [DOI: 10.1016/j.ccr.2023.215021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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5
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Sanchez Arana D, Billups JR, Donnadieu B, Creutz SE. Synthesis and electronic structure of a series of first-row transition-metal pyrazine(diimine) complexes in two oxidation states. J COORD CHEM 2022. [DOI: 10.1080/00958972.2022.2115889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
Affiliation(s)
| | - Jaylan R. Billups
- Department of Chemistry, Mississippi State University, Mississippi State, MS, USA
| | - Bruno Donnadieu
- Department of Chemistry, Mississippi State University, Mississippi State, MS, USA
| | - Sidney E. Creutz
- Department of Chemistry, Mississippi State University, Mississippi State, MS, USA
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6
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Naskar T, Jana M, Majumdar A. Binuclear manganese(II)-thiolate complexes: Synthesis, characterization and nitrite induced structural changes. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.133041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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7
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Massie AA, Kostopoulos N, Grotemeyer EN, Noël J, Jackson TA, Anxolabéhère‐Mallart E. Electrochemical Formation and Reactivity of a Mn‐Peroxo Complex Bearing an Amido N5 Ligand. ChemElectroChem 2022. [DOI: 10.1002/celc.202200112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Allyssa A. Massie
- Department of Chemistry University of Kansas 1567 Irving Hill Road Lawrence KS 66045 USA
| | - Nikolaos Kostopoulos
- Université Paris Cité, CNRS, Laboratoire d'Electrochimie Moléculaire F-75013> Paris France
| | | | - Jean‐Marc Noël
- Université Paris Cité, CNRS, ITODYS F-75013 Paris France
| | - Timothy A. Jackson
- Department of Chemistry University of Kansas 1567 Irving Hill Road Lawrence KS 66045 USA
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8
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Cook EN, Machan CW. Bioinspired mononuclear Mn complexes for O 2 activation and biologically relevant reactions. Dalton Trans 2021; 50:16871-16886. [PMID: 34730590 DOI: 10.1039/d1dt03178c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A general interest in harnessing the oxidizing power of dioxygen (O2) continues to motivate research efforts on bioinspired and biomimetic complexes to better understand how metalloenzymes mediate these reactions. The ubiquity of Fe- and Cu-based enzymes attracts significant attention and has resulted in many noteworthy developments for abiotic systems interested in direct O2 reduction and small molecule activation. However, despite the existence of Mn-based metalloenzymes with important O2-dependent activity, there has been comparatively less focus on the development of these analogues relative to Fe- and Cu-systems. In this Perspective, we summarize important contributions to the development of bioinspired mononuclear Mn complexes for O2 activation and studies on their reactivity, emphasizing important design parameters in the primary and secondary coordination spheres and outlining mechanistic trends.
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Affiliation(s)
- Emma N Cook
- Department of Chemistry, University of Virginia, PO Box 400319, Charlottesville, VA 22904-4319, USA.
| | - Charles W Machan
- Department of Chemistry, University of Virginia, PO Box 400319, Charlottesville, VA 22904-4319, USA.
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9
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Senft L, Moore JL, Franke A, Fisher KR, Scheitler A, Zahl A, Puchta R, Fehn D, Ison S, Sader S, Ivanović-Burmazović I, Goldsmith CR. Quinol-containing ligands enable high superoxide dismutase activity by modulating coordination number, charge, oxidation states and stability of manganese complexes throughout redox cycling. Chem Sci 2021; 12:10483-10500. [PMID: 34447541 PMCID: PMC8356818 DOI: 10.1039/d1sc02465e] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 07/05/2021] [Indexed: 01/01/2023] Open
Abstract
Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for H2O2, [Mn(H2qp1)(MeCN)]2+ and [Mn(H4qp2)Br2], could also catalytically degrade superoxide. Subsequently, [Zn(H2qp1)(OTf)]+ was found to use the redox activity of the H2qp1 ligand to catalyze the conversion of O2˙− to O2 and H2O2, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O2˙− in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O2˙− to confirm the activity and elucidate the catalytic mechanism. The obtained data are consistent with the operation of multiple parallel catalytic cycles, with both the quinol groups and manganese cycling through different oxidation states during the reactions with superoxide. The choice of ligand impacts the overall charges of the intermediates and allows us to visualize complementary sets of intermediates within the catalytic cycles using CSI-MS. With the diquinolic H4qp2, we detect Mn(iii)-superoxo intermediates with both reduced and oxidized forms of the ligand, a Mn(iii)-hydroperoxo compound, and what is formally a Mn(iv)-oxo species with the monoquinolate/mono-para-quinone form of H4qp2. With the monoquinolic H2qp1, we observe a Mn(ii)-superoxo ↔ Mn(iii)-peroxo intermediate with the oxidized para-quinone form of the ligand. The observation of these species suggests inner-sphere mechanisms for O2˙− oxidation and reduction that include both the ligand and manganese as redox partners. The higher positive charges of the complexes with the reduced and oxidized forms of H2qp1 compared to those with related forms of H4qp2 result in higher catalytic activity (kcat ∼ 108 M−1 s−1 at pH 7.4) that rivals those of the most active superoxide dismutase (SOD) mimics. The manganese complex with H2qp1 is markedly more stable in water than other highly active non-porphyrin-based and even some Mn(ii) porphyrin-based SOD mimics. Manganese complexes with polydentate quinol-containing ligands are found to catalyze the degradation of superoxide through inner-sphere mechanisms. The redox activity of the ligand stabilizes higher-valent manganese species.![]()
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Affiliation(s)
- Laura Senft
- Department of Chemistry, Ludwig-Maximilian-University Butenandtstr. 5-13 D 81377 Munich Germany
| | - Jamonica L Moore
- Department of Chemistry and Biochemistry, Auburn University Auburn AL 36849 USA
| | - Alicja Franke
- Department of Chemistry, Ludwig-Maximilian-University Butenandtstr. 5-13 D 81377 Munich Germany
| | - Katherine R Fisher
- Department of Chemistry, Ludwig-Maximilian-University Butenandtstr. 5-13 D 81377 Munich Germany
| | - Andreas Scheitler
- Department of Chemistry and Pharmacy, Friedrich-Alexander University Erlangen-Nuremberg 91058 Erlangen Germany
| | - Achim Zahl
- Department of Chemistry and Pharmacy, Friedrich-Alexander University Erlangen-Nuremberg 91058 Erlangen Germany
| | - Ralph Puchta
- Department of Chemistry and Pharmacy, Friedrich-Alexander University Erlangen-Nuremberg 91058 Erlangen Germany
| | - Dominik Fehn
- Department of Chemistry and Pharmacy, Friedrich-Alexander University Erlangen-Nuremberg 91058 Erlangen Germany
| | - Sidney Ison
- Department of Chemistry and Biochemistry, Auburn University Auburn AL 36849 USA
| | - Safaa Sader
- Department of Chemistry and Biochemistry, Auburn University Auburn AL 36849 USA
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10
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Rydel-Ciszek K. The most reactive iron and manganese complexes with N-pentadentate ligands for dioxygen activation—synthesis, characteristics, applications. REACTION KINETICS MECHANISMS AND CATALYSIS 2021. [PMCID: PMC8204929 DOI: 10.1007/s11144-021-02008-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The iron and manganese complexes that activate oxygen atom play multiple role in technologically relevant reactions as well as in biological transformations, in which exist in different redox states. Among them, high-valent oxo intermediate seems to be the most important one. Iron, and/or manganese-based processes have found application in many areas, starting from catalysis and sustainable technologies, through DNA oxidative cleavage, to new substances useful in chemotherapeutic drugs. This review is not only the latest detailed list of uses of homogeneous N-pentadentate iron and manganese catalysts for syntheses of valuable molecules with huge applications in green technologies, but also a kind of "a cookbook", collecting "recipes" for the discussed complexes, in which the sources necessary to obtain a full characterization of the compounds are presented. Following the catalytic activity of metalloenzymes, and taking into account the ubiquity of iron and manganese salts, which in combination with properly designed ligands may show similarity to natural systems, the discussed complexes can find application as new anti-cancer drugs. Also, owing to ability of oxygen atom to exchange in reaction with H2O, they can be successfully applied in photodriven reactions of water oxidation, as well as in chemically regenerated fuel cells as a redox catalyst.
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Affiliation(s)
- Katarzyna Rydel-Ciszek
- Department of Physical Chemistry, Faculty of Chemistry, Rzeszów University of Technology, al. Powstańców Warszawy 6, P.O. Box 85, 35-959 Rzeszów, Poland
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11
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Downing AN, Coggins MK, Poon PCY, Kovacs JA. Influence of Thiolate versus Alkoxide Ligands on the Stability of Crystallographically Characterized Mn(III)-Alkylperoxo Complexes. J Am Chem Soc 2021; 143:6104-6113. [PMID: 33851827 DOI: 10.1021/jacs.0c13001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The work described herein demonstrates the exquisite control that the inner coordination sphere of metalloenzymes and transition-metal complexes can have on reactivity. We report one of few crystallographically characterized Mn-peroxo complexes and show that the tight correlations between metrical and spectroscopic parameters, established previously by our group for thiolate-ligated RS-Mn(III)-OOR complexes, can be extended to include an alkoxide-ligated RO-Mn(III)-OOR complex. We show that the alkoxide-ligated RO-Mn(III)-OOR complex is an order of magnitude more stable (t1/2298 K = 6730 s, kobs298 K = 1.03 × 10-4 s-1) than its thiolate-ligated RS-Mn(III)-OOR derivative (t1/2293 K = 249 s, k1293 K = 2.78 × 10-3 s-1). Electronic structure calculations provide insight regarding these differences in stability. The highest occupied orbital of the thiolate-ligated derivative possesses significant sulfur character and π-backdonation from the thiolate competes with π-backdonation from the peroxo π*(O-O). DFT-calculated Mulliken charges show that the Mn ion Lewis acidity of alkoxide-ligated RO-Mn(III)-OOR (+0.451) is greater than that of thiolate-ligated RS-Mn(III)-OOR (+0.306), thereby facilitating π-backdonation from the antibonding peroxo π*(O-O) orbital and increasing its stability. This helps to explain why the photosynthetic oxygen-evolving Mn complex, which catalyzes O-O bond formation as opposed to cleavage, incorporates O- and/or N-ligands as opposed to cysS-ligands.
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Affiliation(s)
- Alexandra N Downing
- The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, United States
| | - Michael K Coggins
- The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, United States
| | - Penny Chaau Yan Poon
- The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, United States
| | - Julie A Kovacs
- The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, United States
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12
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Narulkar DD, Ansari A, Vardhaman AK, Harmalkar SS, Lingamallu G, Dhavale VM, Sankaralingam M, Das S, Kumar P, Dhuri SN. A side-on Mn(III)-peroxo supported by a non-heme pentadentate N 3Py 2 ligand: synthesis, characterization and reactivity studies. Dalton Trans 2021; 50:2824-2831. [PMID: 33533342 DOI: 10.1039/d0dt03706k] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A mononuclear manganese(iii)-peroxo complex [MnIII(N3Py2)(O2)]+ (1a) bearing a non-heme N,N'-dimethyl-N-(2-(methyl(pyridin-2-ylmethyl)amino)ethyl)-N'-(pyridin-2-ylmethyl)ethane-1,2-diamine (N3Py2) ligand was synthesized by the reaction of [Mn(N3Py2)(H2O)](ClO4)2 (1) with hydrogen peroxide and triethylamine in CH3CN at 25 °C. The reactivity of 1a in aldehyde deformylation using 2-phenyl propionaldehyde (2-PPA) was studied and the reaction kinetics was monitored by UV-visible spectroscopy. A kinetic isotope effect (KIE) = 1.7 was obtained in the reaction of 1a with 2-PPA and α-[D1]-PPA, suggesting nucleophilic character of 1a. The activation parameters ΔH‡ and ΔS‡ were determined using the Eyring plot while Ea was obtained from the Arrhenius equation by performing the reaction between 288 and 303 K. Hammett constants (σp) of para-substituted benzaldehydes p-X-Ph-CHO (X = Cl, F, H, and Me) were linear with a slope (ρ) = 3.0. Computational study suggested that the side-on structure of 1a is more favored over the end-on structure and facilitates the reactivity of 1a.
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Affiliation(s)
- Dattaprasad D Narulkar
- School of Chemical Sciences, Goa University, Goa-403206, India. and Department of Chemistry, Dnyanprassarak Mandal's College and Research Centre, Assagao, Goa-403507, India
| | - Azaj Ansari
- Department of Chemistry, Central University of Haryana, Mahendergarh-123031, Haryana, India
| | - Anil Kumar Vardhaman
- Polymers & Functional Materials Division, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500007, India
| | | | - Giribabu Lingamallu
- Polymers & Functional Materials Division, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500007, India
| | - Vishal M Dhavale
- CSIR-Central Electrochemical Research Institute, CSIR Madras Complex, Taramani, Chennai-600 113, India
| | - Muniyandi Sankaralingam
- Bioinspired & Biomimetic Inorganic Chemistry Lab, Department of Chemistry, National Institute of Technology Calicut, Kozhikode, Kerala 673601, India
| | - Sandip Das
- Indian Institute of Science Education and Research (IISER), Tirupati-517507, India
| | - Pankaj Kumar
- Indian Institute of Science Education and Research (IISER), Tirupati-517507, India
| | - Sunder N Dhuri
- School of Chemical Sciences, Goa University, Goa-403206, India.
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13
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Zolnhofer EM, Wijeratne GB, Jackson TA, Fortier S, Heinemann FW, Meyer K, Krzystek J, Ozarowski A, Mindiola DJ, Telser J. Electronic Structure and Magnetic Properties of a Titanium(II) Coordination Complex. Inorg Chem 2020; 59:6187-6201. [PMID: 32279487 DOI: 10.1021/acs.inorgchem.0c00311] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Stable coordination complexes of TiII (3d2) are relatively uncommon, but are of interest as synthons for low oxidation state titanium complexes for application as potential catalysts and reagents for organic synthesis. Specifically, high-spin TiII ions supported by redox-inactive ligands are still quite rare due to the reducing power of this soft ion. Among such TiII complexes is trans-[TiCl2(tmeda)2], where tmeda = N,N,N',N'-tetramethylethane-1,2-diamine. This complex was first reported by Gambarotta and co-workers almost 30 years ago, but it was not spectroscopically characterized and theoretical investigation by quantum chemical theory (QCT) was not feasible at that time. As part of our interest in low oxidation state early transition metal complexes, we have revisited this complex and report a modified synthesis and a low temperature (100 K) crystal structure that differs slightly from that originally reported at ambient temperature. We have used magnetometry, high-frequency and -field EPR (HFEPR), and variable-temperature variable-field magnetic circular dichroism (VTVH-MCD) spectroscopies to characterize trans-[TiCl2(tmeda)2]. These techniques yield the following S = 1 spin Hamiltonian parameters for the complex: D = -5.23(1) cm-1, E = -0.88(1) cm-1, (E/D = 0.17), g = [1.86(1), 1.94(2), 1.77(1)]. This information, in combination with electronic transitions from MCD, was used as input for both classical ligand-field theory (LFT) and detailed QCT studies, the latter including both density functional theory (DFT) and ab initio methods. These computational methods are seldom applied to paramagnetic early transition metal complexes, particularly those with S > 1/2. Our studies provide a complete picture of the electronic structure of this complex that can be put into context with the few other high-spin and mononuclear TiII species characterized to date.
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Affiliation(s)
- Eva M Zolnhofer
- Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander University Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
| | - Gayan B Wijeratne
- Department of Chemistry, University of Kansas, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Timothy A Jackson
- Department of Chemistry, University of Kansas, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Skye Fortier
- Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, United States
| | - Frank W Heinemann
- Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander University Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
| | - Karsten Meyer
- Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander University Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
| | - J Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Daniel J Mindiola
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Joshua Telser
- Department of Biological, Physical and Health Sciences, Roosevelt University, Chicago, Illinois 60605, United States
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14
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Rice DB, Massie AA, Jackson TA. Experimental and Multireference ab Initio Investigations of Hydrogen-Atom-Transfer Reactivity of a Mononuclear MnIV-oxo Complex. Inorg Chem 2019; 58:13902-13916. [DOI: 10.1021/acs.inorgchem.9b01761] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Derek B. Rice
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, The University of Kansas, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Allyssa A. Massie
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, The University of Kansas, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
| | - Timothy A. Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, The University of Kansas, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States
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15
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Yan Poon PC, Dedushko MA, Sun X, Yang G, Toledo S, Hayes EC, Johansen A, Piquette MC, Rees JA, Stoll S, Rybak-Akimova E, Kovacs JA. How Metal Ion Lewis Acidity and Steric Properties Influence the Barrier to Dioxygen Binding, Peroxo O-O Bond Cleavage, and Reactivity. J Am Chem Soc 2019; 141:15046-15057. [PMID: 31480847 DOI: 10.1021/jacs.9b04729] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Herein we quantitatively investigate how metal ion Lewis acidity and steric properties influence the kinetics and thermodynamics of dioxygen binding versus release from structurally analogous Mn-O2 complexes, as well as the barrier to Mn peroxo O-O bond cleavage, and the reactivity of Mn oxo intermediates. Previously we demonstrated that the steric and electronic properties of MnIII-OOR complexes containing N-heterocyclic (NAr) ligand scaffolds can have a dramatic influence on alkylperoxo O-O bond lengths and the barrier to alkylperoxo O-O bond cleavage. Herein, we examine the dioxygen reactivity of a new MnII complex containing a more electron-rich, less sterically demanding NAr ligand scaffold, and compare it with previously reported MnII complexes. Dioxygen binding is shown to be reversible with complexes containing the more electron-rich metal ions. The kinetic barrier to O2 binding and peroxo O-O bond cleavage is shown to correlate with redox potentials, as well as the steric properties of the supporting NAr ligands. The reaction landscape for the dioxygen chemistry of the more electron-rich complexes is shown to be relatively flat. A total of four intermediates, including a superoxo and peroxo species, are observed with the most electron-rich complex. Two new intermediates are shown to form following the peroxo, which are capable of cleaving strong X-H bonds. In the absence of a sacrificial H atom donor, solvent, or ligand, serves as a source of H atoms. With TEMPOH as sacrificial H atom donor, a deuterium isotope effect is observed (kH/kD = 3.5), implicating a hydrogen atom transfer (HAT) mechanism. With 1,4-cyclohexadiene, 0.5 equiv of benzene is produced prior to the formation of an EPR detected MnIIIMnIV bimetallic species, and 0.5 equiv after its formation.
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Affiliation(s)
- Penny Chaau Yan Poon
- Department of Chemistry , University of Washington , Campus Box 351700 , Seattle , Washington 98195-1700 , United States
| | - Maksym A Dedushko
- Department of Chemistry , University of Washington , Campus Box 351700 , Seattle , Washington 98195-1700 , United States
| | - Xianru Sun
- Department of Chemistry , Tufts University , 62 Talbot Avenue , Medford , Massachusetts 02155 , United States
| | - Guang Yang
- Department of Chemistry , Tufts University , 62 Talbot Avenue , Medford , Massachusetts 02155 , United States
| | - Santiago Toledo
- The Department of Chemistry , St. Edward's University , 3001 South Congress , Austin , Texas 78704-6489 , United States
| | - Ellen C Hayes
- Department of Chemistry , University of Washington , Campus Box 351700 , Seattle , Washington 98195-1700 , United States
| | - Audra Johansen
- Department of Chemistry , University of Washington , Campus Box 351700 , Seattle , Washington 98195-1700 , United States
| | - Marc C Piquette
- Department of Chemistry , Tufts University , 62 Talbot Avenue , Medford , Massachusetts 02155 , United States
| | - Julian A Rees
- Chemical Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Stefan Stoll
- Department of Chemistry , University of Washington , Campus Box 351700 , Seattle , Washington 98195-1700 , United States
| | - Elena Rybak-Akimova
- Department of Chemistry , Tufts University , 62 Talbot Avenue , Medford , Massachusetts 02155 , United States
| | - Julie A Kovacs
- Department of Chemistry , University of Washington , Campus Box 351700 , Seattle , Washington 98195-1700 , United States
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16
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Geometric and electronic structure of a crystallographically characterized thiolate-ligated binuclear peroxo-bridged cobalt(III) complex. J Biol Inorg Chem 2019; 24:919-926. [PMID: 31342141 DOI: 10.1007/s00775-019-01686-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 07/11/2019] [Indexed: 10/26/2022]
Abstract
In order to shed light on metal-dependent mechanisms for O-O bond cleavage, and its microscopic reverse, we compare herein the electronic and geometric structures of O2-derived binuclear Co(III)- and Mn(III)-peroxo compounds. Binuclear metal peroxo complexes are proposed to form as intermediates during Mn-promoted photosynthetic H2O oxidation, and a Co-containing artificial leaf inspired by nature's photosynthetic H2O oxidation catalyst. Crystallographic characterization of an extremely activated peroxo is made possible by working with substitution-inert, low-spin Co(III). Density functional theory (DFT) calculations show that the frontier orbitals of the Co(III)-peroxo compound differ noticeably from the analogous Mn(III)-peroxo compound. The highest occupied molecular orbital (HOMO) associated with the Co(III)-peroxo is more localized on the peroxo in an antibonding π*(O-O) orbital, whereas the HOMO of the structurally analogous Mn(III)-peroxo is delocalized over both the metal d-orbitals and peroxo π*(O-O) orbital. With low-spin d6 Co(III), filled t2g orbitals prevent π-back-donation from the doubly occupied antibonding π*(O-O) orbital onto the metal ion. This is not the case with high-spin d4 Mn(III), since these orbitals are half-filled. This weakens the peroxo O-O bond of the former relative to the latter.
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17
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18
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A novel manganese(III)-peroxo complex bearing a proline-derived pentadentate aminobenzimidazole ligand. CHINESE CHEM LETT 2018. [DOI: 10.1016/j.cclet.2018.04.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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19
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Denler MC, Wijeratne GB, Rice DB, Colmer HE, Day VW, Jackson TA. Mn III-Peroxo adduct supported by a new tetradentate ligand shows acid-sensitive aldehyde deformylation reactivity. Dalton Trans 2018; 47:13442-13458. [PMID: 30183042 PMCID: PMC6176719 DOI: 10.1039/c8dt02300j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The new tetradentate L7BQ ligand (L7BQ = 1,4-di(quinoline-8-yl)-1,4-diazepane) has been synthesized and shown to support MnII and MnIII-peroxo complexes. X-ray crystallography of the [MnII(L7BQ)(OTf)2] complex shows a monomeric MnII center with the L7BQ ligand providing four donor nitrogen atoms in the equatorial field, with two triflate ions bound in the axial positions. When this species is treated with H2O2 and Et3N at -40 °C, a MnIII-peroxo adduct, [MnIII(O2)(L7BQ)]+ is formed. The formation of this new intermediate is supported by a variety of spectroscopic techniques, including electronic absorption, Mn K-edge X-ray absorption and electron paramagnetic resonance methods. Evaluation of extended X-ray absorption fine structure data for [MnIII(O2)(L7BQ)]+ resolved Mn-O bond distances of 1.85 Å, which are on the short end of those previously reported for crystallographically characterized MnIII-peroxo adducts. An analysis of the X-ray pre-edge region of [MnIII(O2)(L7BQ)]+ revealed a large pre-edge area of 20.8 units. Time-dependent density functional theory computations indicate that the pre-edge intensity is due to Mn 4p-3d mixing caused by geometric distortions from centrosymmetry induced by both the peroxo and L7BQ ligands. The reactivity of [MnIII(O2)(L7BQ)]+ towards aldehydes was assessed through reaction with cyclohexanecarboxaldehyde and 2-phenylpropionaldehyde. From these experiments, it was determined that [MnIII(O2)(L7BQ)]+ only reacts with aldehydes in the presence of acid. Specifically, the addition of cyclohexanecarboxylic acid to [MnIII(O2)(L7BQ)]+ converts the MnIII-peroxo adduct to a new intermediate that could be responsible for the observed aldehyde deformylation activity. These observations underscore the challenges in identifying the reactive metal species in aldehyde deformylation reactions.
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Affiliation(s)
- Melissa C Denler
- The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA.
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20
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Geersing A, Ségaud N, van der Wijst MGP, Rots MG, Roelfes G. Importance of Metal-Ion Exchange for the Biological Activity of Coordination Complexes of the Biomimetic Ligand N4Py. Inorg Chem 2018; 57:7748-7756. [PMID: 29916702 PMCID: PMC6030684 DOI: 10.1021/acs.inorgchem.8b00714] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Indexed: 12/24/2022]
Abstract
Metal coordination complexes can display interesting biological activity, as illustrated by the bleomycins (BLMs), a family of natural antibiotics that when coordinated to a redox-active metal ion, show antitumor activity. Yet, which metal ion is required for the activity in cells is still subject to debate. In this study, we described how different metal ions affect the intracellular behavior and activity of the synthetic BLM-mimic N, N-bis(2-pyridylmethyl)- N-bis(2-pyridyl)methylamine (N4Py). Our study shows that a mixture of iron(II), copper(II), and zinc(II) complexes can be generated when N4Py is added to cell cultures but that the metal ion can also be exchanged by other metal ions present in cells. Moreover, the combination of chemical data, together with the performed biological experiments, shows that the active complex causing oxidative damage to cells is the FeII-N4Py complex and not per se the metal complex that was initially added to the cell culture medium. Finally, it is proposed that the high activity observed upon the addition of the free N4Py ligand is the result of a combination of scavenging of biologically relevant metals and oxidative damage caused by the iron(II) complex.
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Affiliation(s)
- Arjan Geersing
- Stratingh Institute
for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Nathalie Ségaud
- Stratingh Institute
for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Monique G. P. van der Wijst
- Department of Pathology and Medical Biology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands
| | - Marianne G. Rots
- Department of Pathology and Medical Biology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands
| | - Gerard Roelfes
- Stratingh Institute
for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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21
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Rationally designed mimics of antioxidant manganoenzymes: Role of structural features in the quest for catalysts with catalase and superoxide dismutase activity. Coord Chem Rev 2018. [DOI: 10.1016/j.ccr.2018.03.005] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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22
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Rice DB, Massie AA, Jackson TA. Manganese-Oxygen Intermediates in O-O Bond Activation and Hydrogen-Atom Transfer Reactions. Acc Chem Res 2017; 50:2706-2717. [PMID: 29064667 DOI: 10.1021/acs.accounts.7b00343] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Biological systems capitalize on the redox versatility of manganese to perform reactions involving dioxygen and its derivatives superoxide, hydrogen peroxide, and water. The reactions of manganese enzymes influence both human health and the global energy cycle. Important examples include the detoxification of reactive oxygen species by manganese superoxide dismutase, biosynthesis by manganese ribonucleotide reductase and manganese lipoxygenase, and water splitting by the oxygen-evolving complex of photosystem II. Although these enzymes perform very different reactions and employ structurally distinct active sites, manganese intermediates with peroxo, hydroxo, and oxo ligation are commonly proposed in catalytic mechanisms. These intermediates are also postulated in mechanisms of synthetic manganese oxidation catalysts, which are of interest due to the earth abundance of manganese. In this Account, we describe our recent efforts toward understanding O-O bond activation pathways of MnIII-peroxo adducts and hydrogen-atom transfer reactivity of MnIV-oxo and MnIII-hydroxo complexes. In biological and synthetic catalysts, peroxomanganese intermediates are commonly proposed to decay by either Mn-O or O-O cleavage pathways, although it is often unclear how the local coordination environment influences the decay mechanism. To address this matter, we generated a variety of MnIII-peroxo adducts with varied ligand environments. Using parallel-mode EPR and Mn K-edge X-ray absorption techniques, the decay pathway of one MnIII-peroxo complex bearing a bulky macrocylic ligand was investigated. Unlike many MnIII-peroxo model complexes that decay to oxo-bridged-MnIIIMnIV dimers, decay of this MnIII-peroxo adduct yielded mononuclear MnIII-hydroxo and MnIV-oxo products, potentially resulting from O-O bond activation of the MnIII-peroxo unit. These results highlight the role of ligand sterics in promoting the formation of mononuclear products and mark an important step in designing MnIII-peroxo complexes that convert cleanly to high-valent Mn-oxo species. Although some synthetic MnIV-oxo complexes show great potential for oxidizing substrates with strong C-H bonds, most MnIV-oxo species are sluggish oxidants. Both two-state reactivity and thermodynamic arguments have been put forth to explain these observations. To address these issues, we generated a series of MnIV-oxo complexes supported by neutral, pentadentate ligands with systematically perturbed equatorial donation. Kinetic investigations of these complexes revealed a correlation between equatorial ligand-field strength and hydrogen-atom and oxygen-atom transfer reactivity. While this trend can be understood on the basis of the two-state reactivity model, the reactivity trend also correlates with variations in MnIII/IV reduction potential caused by changes in the ligand field. This work demonstrates the dramatic influence simple ligand perturbations can have on reactivity but also illustrates the difficulties in understanding the precise basis for a change in reactivity. In the enzyme manganese lipoxygenase, an active-site MnIII-hydroxo adduct initiates substrate oxidation by abstracting a hydrogen atom from a C-H bond. Precedent for this chemistry from synthetic MnIII-hydroxo centers is rare. To better understand hydrogen-atom transfer by MnIII centers, we developed a pair of MnIII-hydroxo complexes, formed in high yield from dioxygen oxidation of MnII precursors, capable of attacking weak O-H and C-H bonds. Kinetic and computational studies show a delicate interplay between thermodynamic and steric influences in hydrogen-atom transfer reactivity, underscoring the potential of MnIII-hydroxo units as mild oxidants.
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Affiliation(s)
- Derek B. Rice
- Department of Chemistry and
Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045, United States
| | - Allyssa A. Massie
- Department of Chemistry and
Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045, United States
| | - Timothy A. Jackson
- Department of Chemistry and
Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045, United States
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23
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Lo WKC, Castillo CE, Gueret R, Fortage J, Rebarz M, Sliwa M, Thomas F, McAdam CJ, Jameson GB, McMorran DA, Crowley JD, Collomb MN, Blackman AG. Synthesis, Characterization, and Photocatalytic H2-Evolving Activity of a Family of [Co(N4Py)(X)](n+) Complexes in Aqueous Solution. Inorg Chem 2016; 55:4564-81. [PMID: 27064169 DOI: 10.1021/acs.inorgchem.6b00391] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A series of [Co(III)(N4Py)(X)](ClO4)n (X = Cl(-), Br(-), OH(-), N3(-), NCS(-)-κN, n = 2: X = OH2, NCMe, DMSO-κO, n = 3) complexes containing the tetrapyridyl N5 ligand N4Py (N4Py = 1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) has been prepared and fully characterized by infrared (IR), UV-visible, and NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HRESI-MS), elemental analysis, X-ray crystallography, and electrochemistry. The reduced Co(II) and Co(I) species of these complexes have been also generated by bulk electrolyses in MeCN and characterized by UV-visible and EPR spectroscopies. All tested complexes are catalysts for the photocatalytic production of H2 from water at pH 4.0 in the presence of ascorbic acid/ascorbate, using [Ru(bpy)3](2+) as a photosensitizer, and all display similar H2-evolving activities. Detailed mechanistic studies show that while the complexes retain the monodentate X ligand upon electrochemical reduction to Co(II) species in MeCN solution, in aqueous solution, upon reduction by ascorbate (photocatalytic conditions), [Co(II)(N4Py)(HA)](+) is formed in all cases and is the precursor to the Co(I) species which presumably reacts with a proton. These results are in accordance with the fact that the H2-evolving activity does not depend on the chemical nature of the monodentate ligand and differ from those previously reported for similar complexes. The catalytic activity of this series of complexes in terms of turnover number versus catalyst (TONCat) was also found to be dependent on the catalyst concentration, with the highest value of 230 TONCat at 5 × 10(-6) M. As revealed by nanosecond transient absorption spectroscopy measurements, the first electron-transfer steps of the photocatalytic mechanism involve a reductive quenching of the excited state of [Ru(bpy)3](2+) by ascorbate followed by an electron transfer from [Ru(II)(bpy)2(bpy(•-))](+) to the [Co(II)(N4Py)(HA)](+) catalyst. The reduced catalyst then enters into the H2-evolution cycle.
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Affiliation(s)
- Warrick K C Lo
- Department of Chemistry, University of Otago , P. O. Box 56, Dunedin 9054, New Zealand
| | - Carmen E Castillo
- Département de Chimie Moléculaire, CNRS, Université Grenoble Alpes , F-38000 Grenoble, France
| | - Robin Gueret
- Département de Chimie Moléculaire, CNRS, Université Grenoble Alpes , F-38000 Grenoble, France
| | - Jérôme Fortage
- Département de Chimie Moléculaire, CNRS, Université Grenoble Alpes , F-38000 Grenoble, France
| | - Mateusz Rebarz
- Laboratoire de Spectrochimie Infrarouge et Raman, UMR 8516 CNRS-Université Lille 1 Sciences et Technologies , 59655 Villeneuve d'Ascq Cedex, France
| | - Michel Sliwa
- Laboratoire de Spectrochimie Infrarouge et Raman, UMR 8516 CNRS-Université Lille 1 Sciences et Technologies , 59655 Villeneuve d'Ascq Cedex, France
| | - Fabrice Thomas
- Département de Chimie Moléculaire, CNRS, Université Grenoble Alpes , F-38000 Grenoble, France
| | - C John McAdam
- Department of Chemistry, University of Otago , P. O. Box 56, Dunedin 9054, New Zealand
| | - Geoffrey B Jameson
- Institute of Fundamental Sciences, Massey University , P. O. Box 11-222, Palmerston North 4442, New Zealand
| | - David A McMorran
- Department of Chemistry, University of Otago , P. O. Box 56, Dunedin 9054, New Zealand
| | - James D Crowley
- Department of Chemistry, University of Otago , P. O. Box 56, Dunedin 9054, New Zealand
| | - Marie-Noëlle Collomb
- Département de Chimie Moléculaire, CNRS, Université Grenoble Alpes , F-38000 Grenoble, France
| | - Allan G Blackman
- School of Applied Sciences, Auckland University of Technology , Private Bag 92006, Auckland 1142, New Zealand
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24
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Colmer HE, Howcroft AW, Jackson TA. Formation, Characterization, and O-O Bond Activation of a Peroxomanganese(III) Complex Supported by a Cross-Clamped Cyclam Ligand. Inorg Chem 2016; 55:2055-69. [PMID: 26908013 DOI: 10.1021/acs.inorgchem.5b02398] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Although there have been reports describing the nucleophilic reactivity of peroxomanganese(III) intermediates, as well as their conversion to high-valent oxo-bridged dimers, it remains a challenge to activate peroxomanganese(III) species for conversion to high-valent, mononuclear manganese complexes. Herein, we report the generation, characterization, and activation of a peroxomanganese(III) adduct supported by the cross-clamped, macrocyclic Me2EBC ligand (4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). This ligand is known to support high-valent, mononuclear Mn(IV) species with well-defined spectroscopic properties, which provides an opportunity to identify mononuclear Mn(IV) products from O-O bond activation of the corresponding Mn(III)-peroxo adduct. The peroxomanganese(III) intermediate, [Mn(III)(O2)(Me2EBC)](+), was prepared at low-temperature by the addition of KO2 to [Mn(II)(Cl)2(Me2EBC)] in CH2Cl2, and this complex was characterized by electronic absorption, electron paramagnetic resonance (EPR), and Mn K-edge X-ray absorption (XAS) spectroscopies. The electronic structure of the [Mn(III)(O2)(Me2EBC)](+) intermediate was examined by density functional theory (DFT) and time-dependent (TD) DFT calculations. Detailed spectroscopic investigations of the decay products of [Mn(III)(O2)(Me2EBC)](+) revealed the presence of mononuclear Mn(III)-hydroxo species or a mixture of mononuclear Mn(IV) and Mn(III)-hydroxo species. The nature of the observed decay products depended on the amount of KO2 used to generate [Mn(III)(O2)(Me2EBC)](+). The Mn(III)-hydroxo product was characterized by Mn K-edge XAS, and shifts in the pre-edge transition energies and intensities relative to [Mn(III)(O2)(Me2EBC)](+) provide a marker for differences in covalency between peroxo and nonperoxo ligands. To the best of our knowledge, this work represents the first observation of a mononuclear Mn(IV) center upon decay of a nonporphyrinoid Mn(III)-peroxo center.
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Affiliation(s)
- Hannah E Colmer
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
| | - Anthony W Howcroft
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
| | - Timothy A Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , Lawrence, Kansas 66045, United States
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25
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Du J, Xu D, Zhang C, Xia C, Wang Y, Sun W. Synthesis, characterization, and reactivity of a side-on manganese(iii)–peroxo complex bearing a pentadentate aminopyridine ligand. Dalton Trans 2016; 45:10131-5. [DOI: 10.1039/c6dt00508j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A peroxomanganese(iii) species was prepared by the reaction of [Mn(ii)(Pro3Py)(OTf)](OTf) with H2O2/NEt3 and characterized by UV-vis, EPR, ESI-MS and DFT, which exhibited nucleophilic reactivity in aldehyde deformylation.
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Affiliation(s)
- Junyi Du
- State Key Laboratory for Oxo Synthesis and Selective Oxidation
- Lanzhou Institute of Chemical Physics
- Chinese Academy of Sciences
- Lanzhou 730000
- China
| | - Daqian Xu
- State Key Laboratory for Oxo Synthesis and Selective Oxidation
- Lanzhou Institute of Chemical Physics
- Chinese Academy of Sciences
- Lanzhou 730000
- China
| | - Chunxi Zhang
- Laboratory of Photochemistry
- Institute of Chemistry
- Chinese Academy of Sciences
- Beijing
- China
| | - Chungu Xia
- State Key Laboratory for Oxo Synthesis and Selective Oxidation
- Lanzhou Institute of Chemical Physics
- Chinese Academy of Sciences
- Lanzhou 730000
- China
| | - Yong Wang
- State Key Laboratory for Oxo Synthesis and Selective Oxidation
- Lanzhou Institute of Chemical Physics
- Chinese Academy of Sciences
- Lanzhou 730000
- China
| | - Wei Sun
- State Key Laboratory for Oxo Synthesis and Selective Oxidation
- Lanzhou Institute of Chemical Physics
- Chinese Academy of Sciences
- Lanzhou 730000
- China
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26
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Kärkäs MD, Åkermark B. Water oxidation using earth-abundant transition metal catalysts: opportunities and challenges. Dalton Trans 2016; 45:14421-61. [DOI: 10.1039/c6dt00809g] [Citation(s) in RCA: 181] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Catalysts for the oxidation of water are a vital component of solar energy to fuel conversion technologies. This Perspective summarizes recent advances in the field of designing homogeneous water oxidation catalysts (WOCs) based on Mn, Fe, Co and Cu.
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Affiliation(s)
- Markus D. Kärkäs
- Department of Organic Chemistry
- Arrhenius Laboratory
- Stockholm University
- SE-106 91 Stockholm
- Sweden
| | - Björn Åkermark
- Department of Organic Chemistry
- Arrhenius Laboratory
- Stockholm University
- SE-106 91 Stockholm
- Sweden
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27
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Huang XC, Wang HF, Lang JP. Theoretical view on a linear end-on manganese–dioxygen complex bearing a calix[4]arene ligand. RSC Adv 2016. [DOI: 10.1039/c6ra11199h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Mn–O–O angle of mononuclear manganese(iii)-superoxo complexes supported by zwitterionic calix[4]arene ligands can be modulated via solvent polarity perturbations and/or ligand size adjustment as indicated by DFT calculations.
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Affiliation(s)
- Xiang-Cui Huang
- College of Chemistry
- Chemical Engineering and Materials Science
- Soochow University
- Suzhou 215123
- People's Republic of China
| | - Hui-Fang Wang
- College of Chemistry
- Chemical Engineering and Materials Science
- Soochow University
- Suzhou 215123
- People's Republic of China
| | - Jian-Ping Lang
- College of Chemistry
- Chemical Engineering and Materials Science
- Soochow University
- Suzhou 215123
- People's Republic of China
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28
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Wijeratne GB, Zolnhofer EM, Fortier S, Grant LN, Carroll PJ, Chen CH, Meyer K, Krzystek J, Ozarowski A, Jackson TA, Mindiola DJ, Telser J. Electronic Structure and Reactivity of a Well-Defined Mononuclear Complex of Ti(II). Inorg Chem 2015; 54:10380-97. [DOI: 10.1021/acs.inorgchem.5b01796] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Gayan B. Wijeratne
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Eva M. Zolnhofer
- Inorganic Chemistry, Department of Chemistry
and Pharmacy, Friedrich-Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Skye Fortier
- Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, United States
| | - Lauren N. Grant
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Patrick J. Carroll
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Chun-Hsing Chen
- Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, United States
| | - Karsten Meyer
- Inorganic Chemistry, Department of Chemistry
and Pharmacy, Friedrich-Alexander University Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - J. Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Timothy A. Jackson
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
| | - Daniel J. Mindiola
- Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, United States
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Joshua Telser
- Department of
Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605, United States
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29
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Morton J, Akita F, Nakajima Y, Shen JR, Krausz E. Optical identification of the long-wavelength (700–1700 nm) electronic excitations of the native reaction centre, Mn 4 CaO 5 cluster and cytochromes of photosystem II in plants and cyanobacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:153-161. [DOI: 10.1016/j.bbabio.2014.11.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Revised: 10/28/2014] [Accepted: 11/05/2014] [Indexed: 11/30/2022]
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30
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Colmer HE, Geiger RA, Leto DF, Wijeratne GB, Day VW, Jackson TA. Geometric and electronic structure of a peroxomanganese(III) complex supported by a scorpionate ligand. Dalton Trans 2014; 43:17949-63. [PMID: 25312785 PMCID: PMC4237624 DOI: 10.1039/c4dt02483d] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A monomeric Mn(II) complex has been prepared with the facially-coordinating Tp(Ph2) ligand, (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin Mn(II) ion. Treatment of this Mn(II) complex with excess KO2 at room temperature resulted in the formation of a Mn(III)-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate. The electronic structure of this peroxomanganese(III) adduct was examined by using electronic absorption, electron paramagnetic resonance (EPR), low-temperature magnetic circular dichroism (MCD), and variable-temperature variable-field (VTVH) MCD spectroscopies. Density functional theory (DFT), time-dependent (TD)-DFT, and multireference ab initio CASSCF/NEVPT2 calculations were used to assign the electronic transitions and further investigate the electronic structure of the peroxomanganese(III) species. The lowest ligand-field transition in the electronic absorption spectrum of the Mn(III)-O2 complex exhibits a blue shift in energy compared to other previously characterized peroxomanganese(III) complexes that results from a large axial bond elongation, reducing the metal-ligand covalency and stabilizing the σ-antibonding Mn dz(2) MO that is the donor MO for this transition.
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Affiliation(s)
- Hannah E Colmer
- Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA.
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So H, Park YJ, Cho KB, Lee YM, Seo MS, Cho J, Sarangi R, Nam W. Spectroscopic characterization and reactivity studies of a mononuclear nonheme Mn(III)-hydroperoxo complex. J Am Chem Soc 2014; 136:12229-32. [PMID: 25116698 PMCID: PMC4156864 DOI: 10.1021/ja506275q] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Indexed: 12/25/2022]
Abstract
We report the first example of a mononuclear nonheme manganese(III)-hydroperoxo complex derived from protonation of an isolated manganese(III)-peroxo complex bearing an N-tetramethylated cyclam (TMC) ligand, [Mn(III)(TMC)(OOH)](2+). The Mn(III)-hydroperoxo intermediate is characterized with various spectroscopic methods as well as with density functional theory (DFT) calculations, showing the binding of a hydroperoxide ligand in an end-on fashion. The Mn(III)-hydroperoxo species is a competent oxidant in oxygen atom transfer (OAT) reactions, such as the oxidation of sulfides. The electrophilic character of the Mn(III)-hydroperoxo complex is demonstrated unambiguously in the sulfoxidation of para-substituted thioanisoles.
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Affiliation(s)
- Hee So
- Department
of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea
| | - Young Jun Park
- Department
of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea
| | - Kyung-Bin Cho
- Department
of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea
| | - Yong-Min Lee
- Department
of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea
| | - Mi Sook Seo
- Department
of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea
| | - Jaeheung Cho
- Department
of Emerging Materials Science, DGIST, Daegu 711-873, Korea
| | - Ritimukta Sarangi
- Stanford
Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025-7015, United States
| | - Wonwoo Nam
- Department
of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea
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Ching HYV, Anxolabéhère-Mallart E, Colmer HE, Costentin C, Dorlet P, Jackson TA, Policar C, Robert M. Electrochemical formation and reactivity of a manganese peroxo complex: acid driven H2O2 generation vs. O–O bond cleavage. Chem Sci 2014. [DOI: 10.1039/c3sc53469c] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Peroxomanganese complexes as an aid to understanding redox-active manganese enzymes. J Biol Inorg Chem 2013; 19:1-15. [DOI: 10.1007/s00775-013-1067-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Accepted: 11/07/2013] [Indexed: 02/07/2023]
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Yu WF, Meng XG, Peng X, Li XH, Liu Y. Selective oxidation of Mandelic acids catalyzed by copper (II) complexes. ACTA ACUST UNITED AC 2013. [DOI: 10.1016/j.molcata.2013.09.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Kang H, Cho J, Cho KB, Nomura T, Ogura T, Nam W. Mononuclear Manganese-Peroxo and Bis(μ-oxo)dimanganese Complexes Bearing a Common N-Methylated Macrocyclic Ligand. Chemistry 2013; 19:14119-25. [DOI: 10.1002/chem.201301641] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Indexed: 11/08/2022]
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36
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Leto DF, Chattopadhyay S, Day VW, Jackson TA. Reaction landscape of a pentadentate N5-ligated Mn(II) complex with O2˙- and H2O2 includes conversion of a peroxomanganese(III) adduct to a bis(μ-oxo)dimanganese(III,IV) species. Dalton Trans 2013; 42:13014-25. [PMID: 23872704 DOI: 10.1039/c3dt51277k] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Herein we describe the chemical reactivity of the mononuclear [Mn(II)(N4py)(OTf)](OTf) (1) complex with hydrogen peroxide and superoxide. Treatment of 1 with one equivalent superoxide at -40 °C in MeCN formed the peroxomanganese(III) adduct, [Mn(III)(O2)(N4py)](+) (2) in ~30% yield. Complex 2 decayed over time and the formation of the bis(μ-oxo)dimanganese(III,IV) complex, [Mn(III)Mn(IV)(μ-O)2(N4py)2](3+) (3) was observed. When 2 was formed in higher yields (~60%) using excess superoxide, the [Mn(III)(O2)(N4py)](+) species thermally decayed to Mn(II) species and 3 was formed in no greater than 10% yield. Treatment of [Mn(III)(O2)(N4py)](+) with 1 resulted in the formation of 3 in ~90% yield, relative to the concentration of [Mn(III)(O2)(N4py)](+). This reaction mimics the observed chemistry of Mn-ribonucleotide reductase, as it features the conversion of two Mn(II) species to an oxo-bridged Mn(III)Mn(IV) compound using O2(-) as oxidant. Complex 3 was independently prepared through treatment of 1 with H2O2 and base at -40 °C. The geometric and electronic structures of 3 were probed using electronic absorption, electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), variable-temperature, variable-field MCD (VTVH-MCD), and X-ray absorption (XAS) spectroscopies. Complex 3 was structurally characterized by X-ray diffraction (XRD), which revealed the N4py ligand bound in an unusual tetradentate fashion.
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Affiliation(s)
- Domenick F Leto
- Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA.
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Young KJ, Takase MK, Brudvig GW. An anionic N-donor ligand promotes manganese-catalyzed water oxidation. Inorg Chem 2013; 52:7615-22. [PMID: 23777320 PMCID: PMC4040523 DOI: 10.1021/ic400691e] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Four manganese complexes of pentadentate ligands have been studied for their ability to act as oxygen evolution catalysts in the presence of Oxone or hydrogen peroxide. The complexes [Mn(PaPy3)(NO3)](ClO4) (1) (PaPy3H = N,N-bis(2-pyridylmethyl)-amine-N-ethyl-2-pyridine-2-carboxamide) and [Mn(PaPy3)(μ-O)(PaPy3)Mn](ClO4)2 (2) feature an anionic carboxamido ligand trans to the labile sixth coordination site, while [Mn(N4Py)OTf](OTf) (3) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and [Mn(PY5)(OH2)](ClO4)2 (4) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)-pyridine) have neutral ligands of varying flexibility. 1 and 2 are shown to evolve oxygen in the presence of either Oxone or hydrogen peroxide, but 3 evolves oxygen only in the presence of hydrogen peroxide. 4 is inactive. The activity of 1 and 2 with Oxone suggests that the presence of an anionic N-donor ligand plays a role in stabilizing putative high-valent intermediates. Anionic N-donor ligands may be viewed as alternatives to μ-oxo ligands that are prone to protonation in low-valent Mn species formed during a catalytic cycle, resulting in loss of catalyst structure.
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Affiliation(s)
- Karin J. Young
- Department of Chemistry, Yale University, New Haven, CT 06520
| | | | - Gary W. Brudvig
- Department of Chemistry, Yale University, New Haven, CT 06520
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Coggins MK, Sun X, Kwak Y, Solomon EI, Rybak-Akimova E, Kovacs JA. Characterization of metastable intermediates formed in the reaction between a Mn(II) complex and dioxygen, including a crystallographic structure of a binuclear Mn(III)-peroxo species. J Am Chem Soc 2013; 135:5631-40. [PMID: 23470101 PMCID: PMC3709604 DOI: 10.1021/ja311166u] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Transition-metal peroxos have been implicated as key intermediates in a variety of critical biological processes involving O2. Because of their highly reactive nature, very few metal-peroxos have been characterized. The dioxygen chemistry of manganese remains largely unexplored despite the proposed involvement of a Mn-peroxo, either as a precursor to, or derived from, O2, in both photosynthetic H2O oxidation and DNA biosynthesis. These are arguably two of the most fundamental processes of life. Neither of these biological intermediates has been observed. Herein we describe the dioxygen chemistry of coordinatively unsaturated [Mn(II)(S(Me2)N4(6-Me-DPEN))] (+) (1), and the characterization of intermediates formed en route to a binuclear mono-oxo-bridged Mn(III) product {[Mn(III)(S(Me2)N4(6-Me-DPEN)]2(μ-O)}(2+) (2), the oxo atom of which is derived from (18)O2. At low-temperatures, a dioxygen intermediate, [Mn(S(Me2)N4(6-Me-DPEN))(O2)](+) (4), is observed (by stopped-flow) to rapidly and irreversibly form in this reaction (k1(-10 °C) = 3780 ± 180 M(-1) s(-1), ΔH1(++) = 26.4 ± 1.7 kJ mol(-1), ΔS1(++) = -75.6 ± 6.8 J mol(-1) K(-1)) and then convert more slowly (k2(-10 °C) = 417 ± 3.2 M(-1) s(-1), ΔH2(++) = 47.1 ± 1.4 kJ mol(-1), ΔS2(++) = -15.0 ± 5.7 J mol(-1) K(-1)) to a species 3 with isotopically sensitive stretches at νO-O(Δ(18)O) = 819(47) cm(-1), kO-O = 3.02 mdyn/Å, and νMn-O(Δ(18)O) = 611(25) cm(-1) consistent with a peroxo. Intermediate 3 releases approximately 0.5 equiv of H2O2 per Mn ion upon protonation, and the rate of conversion of 4 to 3 is dependent on [Mn(II)] concentration, consistent with a binuclear Mn(O2(2-)) Mn peroxo. This was verified by X-ray crystallography, where the peroxo of {[Mn(III)(S(Me2)N4(6-Me-DPEN)]2(trans-μ-1,2-O2)}(2+) (3) is shown to be bridging between two Mn(III) ions in an end-on trans-μ-1,2-fashion. This represents the first characterized example of a binuclear Mn(III)-peroxo, and a rare case in which more than one intermediate is observed en route to a binuclear μ-oxo-bridged product derived from O2. Vibrational and metrical parameters for binuclear Mn-peroxo 3 are compared with those of related binuclear Fe- and Cu-peroxo compounds.
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Affiliation(s)
- Michael K Coggins
- Department of Chemistry, University of Washington, Campus Box 351700 Seattle, Washington 98195-1700, USA
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Coggins MK, Martin-Diaconescu V, DeBeer S, Kovacs JA. Correlation between structural, spectroscopic, and reactivity properties within a series of structurally analogous metastable manganese(III)-alkylperoxo complexes. J Am Chem Soc 2013; 135:4260-72. [PMID: 23432090 PMCID: PMC3740743 DOI: 10.1021/ja308915x] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Manganese-peroxos are proposed as key intermediates in a number of important biochemical and synthetic transformations. Our understanding of the structural, spectroscopic, and reactivity properties of these metastable species is limited, however, and correlations between these properties have yet to be established experimentally. Herein we report the crystallographic structures of a series of structurally related metastable Mn(III)-OOR compounds, and examine their spectroscopic and reactivity properties. The four reported Mn(III)-OOR compounds extend the number of known end-on Mn(III)-(η(1)-peroxos) to six. The ligand backbone is shown to alter the metal-ligand distances and modulate the electronic properties key to bonding and activation of the peroxo. The mechanism of thermal decay of these metastable species is examined via variable-temperature kinetics. Strong correlations between structural (O-O and Mn···N(py,quin) distances), spectroscopic (E(πv*(O-O) → Mn CT band), ν(O-O)), and kinetic (ΔH(‡) and ΔS(‡)) parameters for these complexes provide compelling evidence for rate-limiting O-O bond cleavage. Products identified in the final reaction mixtures of Mn(III)-OOR decay are consistent with homolytic O-O bond scission. The N-heterocyclic amines and ligand backbone (Et vs Pr) are found to modulate structural and reactivity properties, and O-O bond activation is shown, both experimentally and theoretically, to track with metal ion Lewis acidity. The peroxo O-O bond is shown to gradually become more activated as the N-heterocyclic amines move closer to the metal ion causing a decrease in π-donation from the peroxo πv*(O-O) orbital. The reported work represents one of very few examples of experimentally verified relationships between structure and function.
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Affiliation(s)
- Michael K Coggins
- The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA
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El Ghachtouli S, Vincent Ching HY, Lassalle-Kaiser B, Guillot R, Leto DF, Chattopadhyay S, Jackson TA, Dorlet P, Anxolabéhère-Mallart E. Electrochemical formation of MnIII-peroxo complexes supported by pentadentate amino pyridine and imidazole ligands. Chem Commun (Camb) 2013; 49:5696-8. [DOI: 10.1039/c3cc41300d] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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