1
|
Lin Y, Qiao J, Sun Y, Dong H. The profound review of Fenton process: What's the next step? J Environ Sci (China) 2025; 147:114-130. [PMID: 39003034 DOI: 10.1016/j.jes.2023.10.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Revised: 10/06/2023] [Accepted: 10/07/2023] [Indexed: 07/15/2024]
Abstract
Fenton and Fenton-like processes, which could produce highly reactive species to degrade organic contaminants, have been widely used in the field of wastewater treatment. Therein, the chemistry of Fenton process including the nature of active oxidants, the complicated reactions involved, and the behind reason for its strongly pH-dependent performance, is the basis for the application of Fenton and Fenton-like processes in wastewater treatment. Nevertheless, the conflicting views still exist about the mechanism of the Fenton process. For instance, reaching a unanimous consensus on the nature of active oxidants (hydroxyl radical or tetravalent iron) in this process remains challenging. This review comprehensively examined the mechanism of the Fenton process including the debate on the nature of active oxidants, reactions involved in the Fenton process, and the behind reason for the pH-dependent degradation of contaminants in the Fenton process. Then, we summarized several strategies that promote the Fe(II)/Fe(III) cycle, reduce the competitive consumption of active oxidants by side reactions, and replace the Fenton reagent, thus improving the performance of the Fenton process. Furthermore, advances for the future were proposed including the demand for the high-accuracy identification of active oxidants and taking advantages of the characteristic of target contaminants during the degradation of contaminants by the Fenton process.
Collapse
Affiliation(s)
- Yimin Lin
- State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
| | - Junlian Qiao
- State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
| | - Yuankui Sun
- Department of Environmental Science, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
| | - Hongyu Dong
- Department of Environmental Science, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China.
| |
Collapse
|
2
|
Leahy CA, Drummond MJ, Vura-Weis J, Fout AR. Synthesis of a series of M(II) (M = Mn, Fe, Co) chloride complexes with both inter- and intra-ligand hydrogen bonding interactions. Dalton Trans 2021; 50:12088-12092. [PMID: 34519757 DOI: 10.1039/d1dt02585f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hydrogen bonding networks are vital for metallo-enzymes to function; however, modeling these systems is non-trivial. We report the synthesis of metal chloride (M = Mn, Fe, Co) complexes with intra- and inter-ligand hydrogen bonding interactions. The intra-ligand hydrogen bonds are shown to have a profound effect on the geometry of the metal center.
Collapse
Affiliation(s)
- Clare A Leahy
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, USA.
| | - Michael J Drummond
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, USA.
| | - Josh Vura-Weis
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, USA.
| | - Alison R Fout
- School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, USA.
| |
Collapse
|
3
|
Dobbelaar E, Rauber C, Bonck T, Kelm H, Schmitz M, de Waal Malefijt ME, Klein JEMN, Krüger HJ. Combining Structural with Functional Model Properties in Iron Synthetic Analogue Complexes for the Active Site in Rabbit Lipoxygenase. J Am Chem Soc 2021; 143:13145-13155. [PMID: 34383499 DOI: 10.1021/jacs.1c04422] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Iron complexes that model the structural and functional properties of the active iron site in rabbit lipoxygenase are described. The ligand sphere of the mononuclear pseudo-octahedral cis-(carboxylato)(hydroxo)iron(III) complex, which is completed by a tetraazamacrocyclic ligand, reproduces the first coordination shell of the active site in the enzyme. In addition, two corresponding iron(II) complexes are presented that differ in the coordination of a water molecule. In their structural and electronic properties, both the (hydroxo)iron(III) and the (aqua)iron(II) complex reflect well the only two essential states found in the enzymatic mechanism of peroxidation of polyunsaturated fatty acids. Furthermore, the ferric complex is shown to undergo hydrogen atom abstraction reactions with O-H and C-H bonds of suitable substrates, and the bond dissociation free energy of the coordinated water ligand of the ferrous complex is determined to be 72.4 kcal·mol-1. Theoretical investigations of the reactivity support a concerted proton-coupled electron transfer mechanism in close analogy to the initial step in the enzymatic mechanism. The propensity of the (hydroxo)iron(III) complex to undergo H atom abstraction reactions is the basis for its catalytic function in the aerobic peroxidation of 2,4,6-tri(tert-butyl)phenol and its role as a radical initiator in the reaction of dihydroanthracene with oxygen.
Collapse
Affiliation(s)
- Emiel Dobbelaar
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Christian Rauber
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Thorsten Bonck
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Harald Kelm
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Markus Schmitz
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| | - Matina Eloïse de Waal Malefijt
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
| | - Johannes E M N Klein
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
| | - Hans-Jörg Krüger
- Department of Chemistry, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany
| |
Collapse
|
4
|
Sun C, Oswald VF, Hill EA, Ziller JW, Borovik AS. Investigation of iron-ammine and amido complexes within a C 3-symmetrical phosphinic amido tripodal ligand. Dalton Trans 2021; 50:11197-11205. [PMID: 34338252 DOI: 10.1039/d1dt01032h] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The primary and secondary coordination spheres can have large regulatory effects on the properties of metal complexes. To examine their influences on the properties of monomeric Fe complexes, the tripodal ligand containing phosphinic amido groups, N,N',N''-[nitrilotris(ethane-2,1-diyl)]tris(P,P-diphenylphosphinic amido) ([poat]3-), was used to prepare [FeII/IIIpoat]-/0 complexes. The FeII complex was four-coordinate with 4 N-atom donors comprising the primary coordination sphere. The FeIII complex was six-coordinate with two additional ligands coming from coordination of O-atom donors on two of the phosphinic amido groups in [poat]3-. In the crystalline phase, each complex was part of a cluster containing potassium ions in which KO[double bond, length as m-dash]P interactions served to connect two metal complexes. The [FeII/IIIpoat]-/0 complexes bound an NH3 molecule to form trigonal bipyramidal structures that also formed three intramolecular hydrogen bonds between the ammine ligand and the O[double bond, length as m-dash]P units of [poat]3-. The relatively negative one-electron redox potential of -1.21 V vs. [FeIII/IICp2]+/0 is attributed to the phosphinic amido group of the [poat]3- ligand. Attempts to form the FeIII-amido complex via deprotonation were not conclusive but isolation of [FeIIIpoat(NHtol)]- using the p-toluidine anion was successful, allowing for the full characterization of this complex.
Collapse
Affiliation(s)
- Chen Sun
- Department of Chemistry, University of California-Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, USA.
| | | | | | | | | |
Collapse
|
5
|
Zhang R, Zhou W, Warren JJ. Photo-initiated oxidation of C-H bonds by diimine complexes of vanadium(V). Chem Commun (Camb) 2021; 57:4007-4010. [PMID: 33885690 DOI: 10.1039/d1cc00649e] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The photochemical activation of carbon-hydrogen bonds by vanadium(v)-dioxo and vanadium(v)-oxo-peroxo diimine complexes is described. Reactions were carried out using a selection of organic substrates with C-H bond dissociation free energy values between 70 and 97 kcal mol-1. The ability to activate C-H bonds using vanadium(v)-dioxo and vanadium(v)-oxo-peroxo diimine complexes varies with different bond dissociation free energy. Compounds with weaker C-H bonds are oxidized in minutes, rather than in days for thermal oxidations by the corresponding complexes. Dioxygen is necessary for substrate consumption, which suggests that the electronically excited V complexes are radical reaction initiators via H-atom abstraction from the organic substrate.
Collapse
Affiliation(s)
- Rui Zhang
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby BC V5A 1S6, Canada.
| | - Wen Zhou
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby BC V5A 1S6, Canada.
| | - Jeffrey J Warren
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby BC V5A 1S6, Canada.
| |
Collapse
|
6
|
Keshari K, Bera M, Velasco L, Munshi S, Gupta G, Moonshiram D, Paria S. Characterization and reactivity study of non-heme high-valent iron-hydroxo complexes. Chem Sci 2021; 12:4418-4424. [PMID: 34163706 PMCID: PMC8179568 DOI: 10.1039/d0sc07054h] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A terminal FeIIIOH complex, [FeIII(L)(OH)]2− (1), has been synthesized and structurally characterized (H4L = 1,2-bis(2-hydroxy-2-methylpropanamido)benzene). The oxidation reaction of 1 with one equiv. of tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBAH) or ceric ammonium nitrate (CAN) in acetonitrile at −45 °C results in the formation of a FeIIIOH ligand radical complex, [FeIII(L˙)(OH)]− (2), which is hereby characterized by UV-visible, 1H nuclear magnetic resonance, electron paramagnetic resonance, and X-ray absorption spectroscopy techniques. The reaction of 2 with a triphenylcarbon radical further gives triphenylmethanol and mimics the so-called oxygen rebound step of Cpd II of cytochrome P450. Furthermore, the reaction of 2 was explored with different 4-substituted-2,6-di-tert-butylphenols. Based on kinetic analysis, a hydrogen atom transfer (HAT) mechanism has been established. A pKa value of 19.3 and a BDFE value of 78.2 kcal/mol have been estimated for complex 2. One-electron oxidation of an FeIII–OH complex (1) results in the formation of a FeIII–OH ligand radical complex (2). Its reaction with (C6H5)3C˙ results in the formation of (C6H5)3COH, which is a functional mimic of compound II of cytochrome P450.![]()
Collapse
Affiliation(s)
- Kritika Keshari
- Department of Chemistry, Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India
| | - Moumita Bera
- Department of Chemistry, Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India
| | - Lucía Velasco
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia Calle Faraday, 9 28049 Madrid Spain
| | - Sandip Munshi
- School of Chemical Sciences, Indian Association for the Cultivation of Science 2A & 2B Raja S. C. Mullick Road, Jadavpur Kolkata 700032 India
| | - Geetika Gupta
- Department of Chemistry, Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India
| | - Dooshaye Moonshiram
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia Calle Faraday, 9 28049 Madrid Spain
| | - Sayantan Paria
- Department of Chemistry, Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India
| |
Collapse
|
7
|
Yadav V, Siegler MA, Goldberg DP. Temperature-Dependent Reactivity of a Non-heme Fe III(OH)(SR) Complex: Relevance to Isopenicillin N Synthase. J Am Chem Soc 2021; 143:46-52. [PMID: 33356198 DOI: 10.1021/jacs.0c09688] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Non-heme iron complexes with cis-FeIII(OH)(SAr/OAr) coordination were isolated and examined for their reactivity with a tertiary carbon radical. The sulfur-ligated complex shows a temperature dependence on •OH versus ArS• transfer, whereas the oxygen-ligated complex does not. These results provide the first working model for C-S bond formation in isopenicillin N synthase and indicate that kinetic control may be a key factor in the selectivity of non-heme iron "rebound" processes.
Collapse
Affiliation(s)
- Vishal Yadav
- 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
| |
Collapse
|
8
|
Lee JL, Oswald VF, Biswas S, Hill EA, Ziller JW, Hendrich MP, Borovik AS. Stepwise assembly of heterobimetallic complexes: synthesis, structure, and physical properties. Dalton Trans 2021; 50:8111-8119. [PMID: 34019606 DOI: 10.1039/d1dt01021b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Bimetallic active sites are ubiquitous in metalloenzymes and have sparked investigations of synthetic models to aid in the establishment of structure-function relationship. We previously reported a series of discrete bimetallic complexes with [FeIII-(μ-OH)-MII] cores in which the ligand framework provides distinct binding sites for two metal centers. The formation of these complexes relied on a stepwise synthetic approach in which an FeIII-OH complex containing a sulfonamido tripodal ligand served as a synthon that promoted assembly. We have utilized this approach in the present study to produce a new series of bimetallic complexes with [FeIII-(μ-OH)-MII] cores (M = Ni, Cu, Zn) by using an ancillary ligand to the FeIII center that contains phosphinic amido groups. Assembly began with formation of an FeIII-OH that was subsequently used to bind the MII fragment that contained a triazacyclononane ligand. The series of bimetallic complexes were charactered structurally by X-ray diffraction methods, spectroscopically by absorption, vibrational, electron paramagnetic resonance spectroscopies, and electrochemically by cyclic voltammetry. A notable finding is that these new [FeIII-(μ-OH)-MII] complexes displayed significantly lower reduction potentials than their sulfonamido counterparts, which paves way for future studies on high valent bimetallic complexes in this scaffold.
Collapse
Affiliation(s)
- Justin L Lee
- Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697, USA.
| | - Victoria F Oswald
- Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697, USA.
| | - Saborni Biswas
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
| | - Ethan A Hill
- Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697, USA.
| | - Joseph W Ziller
- Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697, USA.
| | - Michael P Hendrich
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
| | - A S Borovik
- Department of Chemistry, 1102 Natural Sciences II, University of California, Irvine, California 92697, USA.
| |
Collapse
|
9
|
Oswald VF, Lee JL, Biswas S, Weitz AC, Mittra K, Fan R, Li J, Zhao J, Hu MY, Alp EE, Bominaar EL, Guo Y, Green MT, Hendrich MP, Borovik AS. Effects of Noncovalent Interactions on High-Spin Fe(IV)-Oxido Complexes. J Am Chem Soc 2020; 142:11804-11817. [PMID: 32489096 DOI: 10.1021/jacs.0c03085] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
High-valent nonheme FeIV-oxido species are key intermediates in biological oxidation, and their properties are proposed to be influenced by the unique microenvironments present in protein active sites. Microenvironments are regulated by noncovalent interactions, such as hydrogen bonds (H-bonds) and electrostatic interactions; however, there is little quantitative information about how these interactions affect crucial properties of high valent metal-oxido complexes. To address this knowledge gap, we introduced a series of FeIV-oxido complexes that have the same S = 2 spin ground state as those found in nature and then systematically probed the effects of noncovalent interactions on their electronic, structural, and vibrational properties. The key design feature that provides access to these complexes is the new tripodal ligand [poat]3-, which contains phosphinic amido groups. An important structural aspect of [FeIVpoat(O)]- is the inclusion of an auxiliary site capable of binding a Lewis acid (LAII); we used this unique feature to further modulate the electrostatic environment around the Fe-oxido unit. Experimentally, studies confirmed that H-bonds and LAII s can interact directly with the oxido ligand in FeIV-oxido complexes, which weakens the Fe═O bond and has an impact on the electronic structure. We found that relatively large vibrational changes in the Fe-oxido unit correlate with small structural changes that could be difficult to measure, especially within a protein active site. Our work demonstrates the important role of noncovalent interactions on the properties of metal complexes, and that these interactions need to be considered when developing effective oxidants.
Collapse
Affiliation(s)
- Victoria F Oswald
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
| | - Justin L Lee
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
| | - Saborni Biswas
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Andrew C Weitz
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Kaustuv Mittra
- Department of Molecular Biosciences and Biochemistry, University of California at Irvine, Irvine, California 92697, United States
| | - Ruixi Fan
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Jikun Li
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Jiyong Zhao
- Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Michael Y Hu
- Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Esen E Alp
- Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Emile L Bominaar
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Yisong Guo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Michael T Green
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States.,Department of Molecular Biosciences and Biochemistry, University of California at Irvine, Irvine, California 92697, United States
| | - Michael P Hendrich
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - A S Borovik
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
| |
Collapse
|
10
|
Yadav V, Rodriguez RJ, Siegler MA, Goldberg DP. Determining the Inherent Selectivity for Carbon Radical Hydroxylation versus Halogenation with Fe III(OH)(X) Complexes: Relevance to the Rebound Step in Non-heme Iron Halogenases. J Am Chem Soc 2020; 142:7259-7264. [PMID: 32281794 DOI: 10.1021/jacs.0c00493] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The first structural models of the proposed cis-FeIII(OH)(halide) intermediate in the non-heme iron halogenases were synthesized and examined for their inherent reactivity with tertiary carbon radicals. Selective hydroxylation occurs for these cis-FeIII(OH)(X) (X = Cl, Br) complexes in a radical rebound-like process. In contrast, a cis-FeIII(Cl)2 complex reacts with carbon radicals to give halogenation. These results are discussed in terms of the inherent reactivity of the analogous rebound intermediate in both enzymes and related catalysts.
Collapse
Affiliation(s)
- Vishal Yadav
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Rodolfo J Rodriguez
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Maxime A Siegler
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David P Goldberg
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States
| |
Collapse
|
11
|
Gordon Z, Miller TJ, Leahy CA, Matson EM, Burgess M, Drummond MJ, Popescu CV, Smith CM, Lord RL, Rodríguez-López J, Fout AR. Characterization of Terminal Iron(III)-Oxo and Iron(III)-Hydroxo Complexes Derived from O 2 Activation. Inorg Chem 2019; 58:15801-15811. [PMID: 31714068 DOI: 10.1021/acs.inorgchem.9b02079] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
O2 activation at nonheme iron centers is a common motif in biological systems. While synthetic models have provided numerous insights into the reactivity of high-valent iron-oxo complexes related to biological processes, the majority of these complexes are synthesized using alternative oxidants. This report describes O2 activation by an iron(II)-triflate complex of the imino-functionalized tris(pyrrol-2-ylmethyl)amine ligand framework, H3[N(piCy)3]. Initial reaction conditions result in the formation of a mixture of oxidation products including terminal iron(III)-oxo and iron(III)-hydroxo complexes. The relevance of these species to the O2 activation process is demonstrated through reactivity studies and electrochemical analysis of the iron(III)-oxo complex.
Collapse
Affiliation(s)
- Zachary Gordon
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Tabitha J Miller
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Clare A Leahy
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Ellen M Matson
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Mark Burgess
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Michael J Drummond
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Codrina V Popescu
- Department of Chemistry , University of St. Thomas , 2115 Summit Avenue , St. Paul , Minnesota 55105 , United States
| | - Connor M Smith
- Department of Chemistry , University of St. Thomas , 2115 Summit Avenue , St. Paul , Minnesota 55105 , United States
| | - Richard L Lord
- Department of Chemistry , Grand Valley State University , 1 Campus Drive Allendale , Michigan 49401 , United States
| | - Joaquín Rodríguez-López
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Alison R Fout
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| |
Collapse
|
12
|
Yadav V, Gordon JB, Siegler MA, Goldberg DP. Dioxygen-Derived Nonheme Mononuclear Fe III(OH) Complex and Its Reactivity with Carbon Radicals. J Am Chem Soc 2019; 141:10148-10153. [PMID: 31244183 DOI: 10.1021/jacs.9b03329] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A new tetradentate, monoanionic, mixed N/O donor ligand (BNPAPh2O-) with second coordination sphere H-bonding groups has been synthesized for stabilization of a terminal FeIII(OH) complex. The complex FeII(BNPAPh2O)(OTf) (1) reacts with O2 to give a mononuclear terminal FeIII(OH) complex, FeIII(OH)(BNPAPh2O)(OTf) (2), both of which were characterized by X-ray diffraction, electrospray ionization mass spectrometry, UV-vis, 1H and 19F nuclear magnetic resonance, 57Fe Mössbauer, and electron paramagnetic resonance spectroscopies. Treatment of 2 with carbon radicals (Ar3C·) gives Ar3COH and the FeII complex 1, in direct analogy with the elusive radical "rebound" process proposed for nonheme iron enzymes.
Collapse
Affiliation(s)
- Vishal Yadav
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Jesse B Gordon
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Maxime A Siegler
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - David P Goldberg
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| |
Collapse
|
13
|
Drummond MJ, Ford CL, Gray DL, Popescu CV, Fout AR. Radical Rebound Hydroxylation Versus H-Atom Transfer in Non-Heme Iron(III)-Hydroxo Complexes: Reactivity and Structural Differentiation. J Am Chem Soc 2019; 141:6639-6650. [PMID: 30969766 DOI: 10.1021/jacs.9b01516] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The characterization of high-valent iron centers in enzymes has been aided by synthetic model systems that mimic their reactivity or structural and spectral features. For example, the cleavage of dioxygen often produces an iron(IV)-oxo that has been characterized in a number of enzymatic and synthetic systems. In non-heme 2-oxogluterate dependent (iron-2OG) enzymes, the ferryl species abstracts an H-atom from bound substrate to produce the proposed iron(III)-hydroxo and caged substrate radical. Most iron-2OG enzymes perform a radical rebound hydroxylation at the site of the H-atom abstraction (HAA); however, recent reports have shown that certain substrates can be desaturated through the loss of a second H atom at a site adjacent to a heteroatom (N or O) for most native desaturase substrates. One proposed mechanism for the removal of the second H-atom involves a polar-cleavage mechanism (electron transfer-proton transfer) by the iron(III)-hydroxo, as opposed to a second HAA. Herein we report the synthesis and characterization of a series of iron complexes with hydrogen bonding interactions between bound aquo or hydroxo ligands and the secondary coordination sphere in ferrous and ferric complexes. Interconversion among the iron species is accomplished by stepwise proton or electron addition or subtraction, as well as H-atom transfer (HAT). The calculated bond dissociation free energies (BDFEs) of two ferric hydroxo complexes, differentiated by their noncovalent interactions and reactivity, suggest that neither complex is capable of activating even weak C-H bonds, lending further support to the proposed mechanism for desaturation in iron-2OG desaturase enzymes. Additionally, the ferric hydroxo species are differentiated by their reactivity toward performing a radical rebound hydroxylation of triphenylmethylradical. Our findings should encourage further study of the desaturase systems that may contain unique H-bonding motifs proximal to the active site that help bias substrate desaturation over hydroxylation.
Collapse
Affiliation(s)
- Michael J Drummond
- School of Chemical Sciences , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Courtney L Ford
- School of Chemical Sciences , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Danielle L Gray
- School of Chemical Sciences , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| | - Codrina V Popescu
- Department of Chemistry , University of Saint Thomas , 2115 Summit Avenue , Saint Paul , Minnesota 55105 , United States
| | - Alison R Fout
- School of Chemical Sciences , University of Illinois at Urbana-Champaign , 600 South Mathews Avenue , Urbana , Illinois 61801 , United States
| |
Collapse
|
14
|
Schulte KA, Vignesh KR, Dunbar KR. Effects of coordination sphere on unusually large zero field splitting and slow magnetic relaxation in trigonally symmetric molecules. Chem Sci 2018; 9:9018-9026. [PMID: 30647894 PMCID: PMC6301199 DOI: 10.1039/c8sc02820f] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 09/15/2018] [Indexed: 01/29/2023] Open
Abstract
Geometric control in mononuclear complexes has come to the forefront in the field of molecular magnets due to its profound effects on relaxation pathways and blocking temperature in single molecule magnets (SMMs). Herein we report the synthesis and magnetic characterization of six trigonally symmetric, divalent Fe, Co, and Ni molecules, with the rigid geometry enforced via the use of the tris-anionic, tetradentate ligand MST (N,N',N''-[2,2',2''-nitrilotris-(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamide)). A systematic study on the effect of converting between trigonal monopyramidal complexes, (Me4N)[M(MST)], and trigonal bipyramidal complexes, (Me4N)[M(MST)(OH2)] was conducted experimentally and computationally. It was found that (Me4N)[Ni(MST)] exhibits a very large, near record zero-field splitting parameter (D) value of -434 cm-1, owing to an extremely low lying first excited state. The trigonal monopyramidal cobalt and iron complexes exhibit slow magnetic relaxation under applied fields, resulting in barriers of 45 K and 63.9 K respectively. Coordination of a single water molecule in the open axial site of the trigonal monopyramidal complexes exerts drastic dampening effects on the D value as well as slow relaxation. Computations reveal that coordination of water rotates the D zz axis away from the C 3 axis of symmetry resulting in a smaller D value. The aquo species (Me4N)[Co(MST)(OH2)] also exhibits magnetic relaxation under an applied field, but the barrier is reduced to 9.9 K. Water coordination totally quenches the magnetic behavior in the iron complex, and reduces the D value for nickel to -185 cm-1. These results showcase the drastic effect that a small change in the coordination environment can have on magnetic behavior, as well as that trigonal monopyramidal geometry can lead to near record D values.
Collapse
Affiliation(s)
- Kelsey A Schulte
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , USA .
| | - Kuduva R Vignesh
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , USA .
| | - Kim R Dunbar
- Department of Chemistry , Texas A&M University , College Station , Texas 77843 , USA .
| |
Collapse
|
15
|
Lau N, Sano Y, Ziller JW, Borovik AS. Modular bimetallic complexes with a sulfonamido-based ligand. Dalton Trans 2018; 47:12362-12372. [PMID: 30118133 PMCID: PMC6165629 DOI: 10.1039/c8dt02455c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A series of bimetallic complexes prepared with the ligands N,N,N',N'-tetramethylethane-1,2-diamine (TMEDA) and N,N',N''-[2,2',2''-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido) ([MST]3-) is described. Four diiron compounds of the formulation (TMEDA)FeII(X)-(μ-OH)-FeIIIMST were prepared, in which the X- ligands are the anions OTf-, Br-, SCN-, or N3-. Additionally, two heterobimetallic compounds of the formulation (TMEDA)MII(OTf)-(μ-OH)-FeIIIMST (MII = CoII or NiII) were synthesized. All these compounds have similar spectroscopic and structural properties. The diiron compounds exhibit perpendicular-mode electron paramagnetic resonance spectra consistent with S = 1/2 spin ground states, which is expected for high-spin FeII and FeIII centres that are antiferromagnetically coupled. The heterobimetallic (TMEDA)NiII(OTf)-(μ-OH)-FeIIIMST complex had a spin state of S = 3/2 that also resulted from antiferromagnetic coupling between the high-spin NiII and FeIII centres. The modularity of this system is further demonstrated by the substitution of the TMEDA ligand with ethylenediamine (en); for this species two equivalents of en coordinate to the FeII centre to form [(en)2FeII-(μ-OH)-FeIIIMST]OTf. These results demonstrate that a modular bimetallic system has been developed in which the key components can be modified.
Collapse
Affiliation(s)
- Nathanael Lau
- Department of Chemistry, University of California - Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, USA.
| | | | | | | |
Collapse
|
16
|
Cook SA, Bogart JA, Levi N, Weitz AC, Moore C, Rheingold AL, Ziller JW, Hendrich MP, Borovik AS. Mononuclear complexes of a tridentate redox-active ligand with sulfonamido groups: structure, properties, and reactivity. Chem Sci 2018; 9:6540-6547. [PMID: 30310585 PMCID: PMC6115676 DOI: 10.1039/c7sc05445a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2017] [Accepted: 06/30/2018] [Indexed: 12/16/2022] Open
Abstract
The design of molecular complexes of earth-abundant first-row transition metals that can catalyze multi-electron C-H bond activation processes is of interest for achieving efficient, low-cost syntheses of target molecules. To overcome the propensity of these metals to perform single-electron processes, redox-active ligands have been utilized to provide additional electron equivalents. Herein, we report the synthesis of a novel redox active ligand, [ibaps]3-, which binds to transition metals such as FeII and CoII in a meridional fashion through the three anionic nitrogen atoms and provides additional coordination sites for other ligands. In this study, the neutral bidentate ligand 2,2'-bipyridine (bpy) was used to complete the coordination spheres of the metal ions and form NEt4[MII(ibaps)bpy] (M = Fe (1) or Co (1-Co)) salts. The FeII salt exhibited rich electrochemical properties and could be chemically oxidized by 1 and 2 equiv. of ferrocenium to form singly and doubly oxidized species, respectively. The reactivity of 1 towards intramolecular C-H bond amination of aryl azides at benzylic and aliphatic carbon centers was explored, and moderate to good yields of the resulting indoline products were obtained.
Collapse
Affiliation(s)
- Sarah A Cook
- Department of Chemistry , University of California-Irvine , 1102 Natural Sciences II , Irvine , California 92697 , USA .
| | - Justin A Bogart
- Department of Chemistry , University of California-Irvine , 1102 Natural Sciences II , Irvine , California 92697 , USA .
| | - Noam Levi
- Department of Chemistry , University of California-Irvine , 1102 Natural Sciences II , Irvine , California 92697 , USA .
| | - Andrew C Weitz
- Department of Chemistry , Carnegie Melon University , Pittsburgh , Pennsylvania 15213 , USA
| | - Curtis Moore
- Department of Chemistry and Biochemistry , University of California-San Diego , San Diego , California 92093 , USA
| | - Arnold L Rheingold
- Department of Chemistry and Biochemistry , University of California-San Diego , San Diego , California 92093 , USA
| | - Joseph W Ziller
- Department of Chemistry , University of California-Irvine , 1102 Natural Sciences II , Irvine , California 92697 , USA .
| | - Michael P Hendrich
- Department of Chemistry , Carnegie Melon University , Pittsburgh , Pennsylvania 15213 , USA
| | - A S Borovik
- Department of Chemistry , University of California-Irvine , 1102 Natural Sciences II , Irvine , California 92697 , USA .
| |
Collapse
|
17
|
Wallen CM, Bacsa J, Scarborough CC. Coordination of Hydrogen Peroxide with Late-Transition-Metal Sulfonamido Complexes. Inorg Chem 2017; 57:4841-4848. [DOI: 10.1021/acs.inorgchem.7b02514] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Christian M. Wallen
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - John Bacsa
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | | |
Collapse
|
18
|
Sano Y, Lau N, Weitz AC, Ziller JW, Hendrich MP, Borovik A. Models for Unsymmetrical Active Sites in Metalloproteins: Structural, Redox, and Magnetic Properties of Bimetallic Complexes with M II-(μ-OH)-Fe III Cores. Inorg Chem 2017; 56:14118-14128. [PMID: 29112385 PMCID: PMC5696092 DOI: 10.1021/acs.inorgchem.7b02230] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Bimetallic complexes are important sites in metalloproteins but are often difficult to prepare synthetically. We have previously introduced an approach to form discrete bimetallic complexes with MII-(μ-OH)-FeIII (MII = Mn, Fe) cores using the tripodal ligand N,N',N″-[2,2',2″-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido) ([MST]3-). This series is extended to include the rest of the late 3d transition metal ions (MII = Co, Ni, Cu, Zn). All of the bimetallic complexes have similar spectroscopic and structural properties that reflect little change despite varying the MII centers. Magnetic studies performed on the complexes in solution using electron paramagnetic resonance spectroscopy showed that the observed spin states varied incrementally from S = 0 through S = 5/2; these results are consistent with antiferromagnetic coupling between the high-spin MII and FeIII centers. However, the difference in the MII ion occupancy yielded only slight changes in the magnetic exchange coupling strength, and all complexes had J values ranging from +26(4) to +35(3) cm-1.
Collapse
Affiliation(s)
- Yohei Sano
- Department of Chemistry, University of California – Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| | - Nathanael Lau
- Department of Chemistry, University of California – Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| | - Andrew C. Weitz
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, United States
| | - Joseph W. Ziller
- Department of Chemistry, University of California – Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| | - Michael P. Hendrich
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, United States
| | - A.S. Borovik
- Department of Chemistry, University of California – Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| |
Collapse
|
19
|
Ching WM, Zhou A, Klein JEMN, Fan R, Knizia G, Cramer CJ, Guo Y, Que L. Correction to Characterization of the Fleeting Hydroxoiron(III) Complex of the Pentadentate TMC-py Ligand. Inorg Chem 2017; 56:13627. [DOI: 10.1021/acs.inorgchem.7b02374] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
20
|
Lau N, Sano Y, Ziller JW, Borovik AS. Terminal Ni II-OH/-OH 2 complexes in trigonal bipyramidal geometries derived from H 2O. Polyhedron 2017; 125:179-185. [PMID: 29170577 PMCID: PMC5695699 DOI: 10.1016/j.poly.2016.11.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The preparation and characterization of two NiII complexes are described, a terminal NiII-OH complex with the tripodal ligand tris[(N)-tertbutylureaylato)-N-ethyl)]aminato ([H3buea]3-) and a terminal Ni II-OH2 complex with the tripodal ligand N,N',N″-[2,2',2″-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido) ([MST]3-). For both complexes, the source of the -OH and -OH2 ligand is water. The salts K2[NiIIH3buea(OH)] and NMe4[NiIIMST(OH2)] were characterized using perpendicular-mode X-band electronic paramagnetic resonance, Fourier transform infrared, UV-visible spectroscopies, and its electrochemical properties were evaluated using cyclic voltammetry. The solid state structures of these complexes determined by X-ray diffraction methods reveal that they adopt a distorted trigonal bipyramidal geometry, an unusual structure for 5-coordinate NiII complexes. Moreover, the NiII-OH and NiII-OH2 units form intramolecular hydrogen bonding networks with the [H3buea]3- and [MST]3- ligands. The oxidation chemistry of these complexes was explored by treating the high-spin NiII compounds with one-electron oxidants. Species were formed with S = 1/2 spin ground states that are consistent with formation of monomeric NiIII species. While the formation of NiIII-OH complexes cannot be ruled out, the lack of observable O-H vibrations from the putative Ni-OH units suggest the possibility that other high valent Ni species are formed.
Collapse
Affiliation(s)
- Nathanael Lau
- Department of Chemistry, University of California - Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| | - Yohei Sano
- Department of Chemistry, University of California - Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| | - Joseph W Ziller
- Department of Chemistry, University of California - Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| | - A S Borovik
- Department of Chemistry, University of California - Irvine, 1102 Natural Sciences II, Irvine, CA 92697-2025, United States
| |
Collapse
|
21
|
de Ruiter G, Thompson NB, Takase MK, Agapie T. Intramolecular C-H and C-F Bond Oxygenation Mediated by a Putative Terminal Oxo Species in Tetranuclear Iron Complexes. J Am Chem Soc 2016; 138:1486-9. [PMID: 26760217 PMCID: PMC4871154 DOI: 10.1021/jacs.5b12214] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Herein we report the intramolecular arene C-H and C-F bond oxygenation by tetranuclear iron complexes. Treatment of [LFe3(PhPz)3OFe][OTf]2 (1) or its fluorinated analog [LFe3(F2ArPz)3OFe][OTf]2 (5) with iodosobenzene results in the regioselective hydroxylation of a bridging pyrazolate ligand, converting a C-H or C-F bond into a C-O bond. The observed reactivity suggests the formation of terminal and reactive Fe-oxo intermediates. With the possibility of intramolecular electron transfer within clusters in 1 and 5, different reaction pathways (Fe(IV)-oxo vs Fe(III)-oxo) might be responsible for the observed arene hydroxylation.
Collapse
Affiliation(s)
- Graham de Ruiter
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Niklas B. Thompson
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Michael K. Takase
- 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
| |
Collapse
|
22
|
Wallen CM, Wielizcko M, Bacsa J, Scarborough CC. Heterotrimetallic sandwich complexes supported by sulfonamido ligands. Inorg Chem Front 2016. [DOI: 10.1039/c5qi00233h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
CoII complexes bearing sulfonamido ligands derived from tris(2-aminoethyl)amine (H6tren) assemble into complex architectures in the presence of Group II ions through interactions between the Group II ion and the sulfonyl oxygens.
Collapse
Affiliation(s)
| | | | - John Bacsa
- Department of Chemistry
- Emory University
- Atlanta
- USA
| | | |
Collapse
|
23
|
Abstract
Metal(H2O2) complexes have been implicated in kinetic and computational studies but have never been observed. Accordingly, H2O2 has been described as a very weak ligand. We report the first metal(H2O2) adduct, which is made possible by incorporating intramolecular hydrogen-bonding interactions with bound H2O2. This Zn(II)(H2O2) complex decays in solution by a second-order process that is slow enough to enable characterization of this species by X-ray crystallography. This report speaks to the intermediacy of metal(H2O2) adducts in chemistry and biology and opens the door to exploration of these species in oxidation catalysis.
Collapse
Affiliation(s)
- Christian M Wallen
- Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - John Bacsa
- Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| | - Christopher C Scarborough
- Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States
| |
Collapse
|
24
|
Cook SA, Borovik AS. Molecular designs for controlling the local environments around metal ions. Acc Chem Res 2015; 48:2407-14. [PMID: 26181849 DOI: 10.1021/acs.accounts.5b00212] [Citation(s) in RCA: 232] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The functions of metal complexes are directly linked to the local environment in which they are housed; modifications to the local environment (or secondary coordination sphere) are known to produce changes in key properties of the metal centers that can affect reactivity. Noncovalent interactions are the most common and influential forces that regulate the properties of secondary coordination spheres, which leads to complexities in structure that are often difficult to achieve in synthetic systems. Using key architectural features from the active sites of metalloproteins as inspiration, we have developed molecular systems that enforce intramolecular hydrogen bonds (H-bonds) around a metal center via incorporation of H-bond donors and acceptors into rigid ligand scaffolds. We have utilized these molecular species to probe mechanistic aspects of biological dioxygen activation and water oxidation. This Account describes the stabilization and characterization of unusual M-oxo and heterobimetallic complexes. These types of species have been implicated in a range of oxidative processes in biology but are often difficult to study because of their inherent reactivity. Our H-bonding ligand systems allowed us to prepare an Fe(III)-oxo species directly from the activation of O2 that was subsequently oxidized to form a monomeric Fe(IV)-oxo species with an S = 2 spin state, similar to those species proposed as key intermediates in non-heme monooxygenases. We also demonstrated that a single Mn(III)-oxo center that was prepared from water could be converted to a high-spin Mn(V)-oxo species via stepwise oxidation, a process that mimics the oxidative charging of the oxygen-evolving complex (OEC) of photosystem II. Current mechanisms for photosynthetic O-O bond formation invoke a Mn(IV)-oxyl species rather than the isoelectronic Mn(V)-oxo system as the key oxidant based on computational studies. However, there is no experimental information to support the existence of a Mn-oxyl radical. We therefore probed the amount of spin density on the oxido ligand of our complexes using EPR spectroscopy in conjunction with oxygen-17 labeling. Our findings showed that there is a significant amount of spin on the oxido ligand, yet the M-oxo bonds are best described as highly covalent and there is no indication that an oxyl radical is formed. These results offer the intriguing possibility that high-spin M-oxo complexes are involved in O-O bond formation in biology. Ligand redesign to incorporate H-bond accepting units (sulfonamido groups) simultaneously provided a metal ion binding pocket, adjacent H-bond acceptors, and an auxiliary binding site for a second metal ion. These properties allowed us to isolate a series of heterobimetallic complexes of Fe(III) and Mn(III) in which a group II metal ion was coordinated within the secondary coordination sphere. Examination of the influence of the second metal ion on the electron transfer properties of the primary metal center revealed unexpected similarities between Ca(II) and Sr(II) ions, a result with relevance to the OEC. In addition, the presence of a second metal ion was found to prevent intramolecular oxidation of the ligand with an O atom transfer reagent.
Collapse
Affiliation(s)
- Sarah A. Cook
- Department
of Chemistry, University of California—Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - A. S. Borovik
- Department
of Chemistry, University of California—Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| |
Collapse
|