1
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Partial synthetic models of FeMoco with sulfide and carbyne ligands: Effect of interstitial atom in nitrogenase active site. Proc Natl Acad Sci U S A 2021; 118:2109241118. [PMID: 34857636 DOI: 10.1073/pnas.2109241118] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/29/2021] [Indexed: 01/13/2023] Open
Abstract
Nitrogen-fixing organisms perform dinitrogen reduction to ammonia at an Fe-M (M = Mo, Fe, or V) cofactor (FeMco) of nitrogenase. FeMco displays eight metal centers bridged by sulfides and a carbide having the MFe7S8C cluster composition. The role of the carbide ligand, a unique motif in protein active sites, remains poorly understood. Toward addressing how the carbon bridge affects the physical and chemical properties of the cluster, we isolated synthetic models of subsite MFe3S3C displaying sulfides and a chelating carbyne ligand. We developed synthetic protocols for structurally related clusters, [Tp*M'Fe3S3X]n-, where M' = Mo or W, the bridging ligand X = CR, N, NR, S, and Tp* = Tris(3,5-dimethyl-1-pyrazolyl)hydroborate, to study the effects of the identity of the heterometal and the bridging X group on structure and electrochemistry. While the nature of M' results in minor changes, the chelating, μ3-bridging carbyne has a large impact on reduction potentials, being up to 1 V more reducing compared to nonchelating N and S analogs.
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2
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Joseph C, Cobb CR, Rose MJ. Single-Step Sulfur Insertions into Iron Carbide Carbonyl Clusters: Unlocking the Synthetic Door to FeMoco Analogues. Angew Chem Int Ed Engl 2021; 60:3433-3437. [PMID: 33089646 DOI: 10.1002/anie.202011517] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Revised: 10/09/2020] [Indexed: 11/09/2022]
Abstract
The one-step syntheses, X-ray structures, and spectroscopic characterization of synthetic iron clusters, bearing either inorganic sulfides or thiolate with interstitial carbide motifs, are reported. Treatment of iron carbide carbonyl clusters [Fen (μn -C)(CO)m ]x (n=5,6; m=15,16; x=0,-2) with electrophilic sulfur sources (S2 Cl2 , S8 ) results in the formation of several μ4 -S dimers of clusters, and moreover, iron-sulfide-(sulfocarbide) clusters. The core sulfocarbide unit {C-S}4- serves as a structural model for a proposed intermediate in the radical S-adenosyl-L-methionine biogenesis of the M-cluster. Furthermore, the electrophilic sulfur strategy has been extended to provide the first ever thiolato-iron-carbide complex: an analogous reaction with toluylsulfenyl chloride affords the cluster [Fe5 (μ5 -C)(SC7 H7 )(CO)13 ]- . The strategy described herein provides a breakthrough towards developing syntheses of biomimetic iron-sulfur-carbide clusters like FeMoco.
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Affiliation(s)
- Chris Joseph
- Department of Chemistry, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Caitlyn R Cobb
- Department of Chemistry, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Michael J Rose
- Department of Chemistry, The University of Texas at Austin, Austin, TX, 78712, USA
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3
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Joseph C, Cobb CR, Rose MJ. Single‐Step Sulfur Insertions into Iron Carbide Carbonyl Clusters: Unlocking the Synthetic Door to FeMoco Analogues. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202011517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Chris Joseph
- Department of Chemistry The University of Texas at Austin Austin TX 78712 USA
| | - Caitlyn R. Cobb
- Department of Chemistry The University of Texas at Austin Austin TX 78712 USA
| | - Michael J. Rose
- Department of Chemistry The University of Texas at Austin Austin TX 78712 USA
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4
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Construction of Synthetic Models for Nitrogenase-Relevant NifB Biogenesis Intermediates and Iron-Carbide-Sulfide Clusters. Catalysts 2020. [DOI: 10.3390/catal10111317] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The family of nitrogenase enzymes catalyzes the reduction of atmospheric dinitrogen (N2) to ammonia under remarkably benign conditions of temperature, pressure, and pH. Therefore, the development of synthetic complexes or materials that can similarly perform this reaction is of critical interest. The primary obstacle for obtaining realistic synthetic models of the active site iron-sulfur-carbide cluster (e.g., FeMoco) is the incorporation of a truly inorganic carbide. This review summarizes the present state of knowledge regarding biological and chemical (synthetic) incorporation of carbide into iron-sulfur clusters. This includes the Nif cluster of proteins and associated biochemistry involved in the endogenous biogenesis of FeMoco. We focus on the chemical (synthetic) incorporation portion of our own efforts to incorporate and modify C1 units in iron/sulfur clusters. We also highlight recent contributions from other research groups in the area toward C1 and/or inorganic carbide insertion.
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5
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Capel Berdiell I, Kulmaczewski R, Warriner SL, Cespedes O, Halcrow MA. Iron and Silver Complexes of 4‐(Imidazol‐1‐yl)‐2,6‐di(pyrazol‐1‐yl)‐pyridine (
L
), Including a [Fe
3
(µ‐F)
2
F
6
L
8
]
+
Assembly. Eur J Inorg Chem 2020. [DOI: 10.1002/ejic.202000782] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
| | | | | | - Oscar Cespedes
- School of Physics and Astronomy University of Leeds EC Stoner Building LS2 9JT Leeds UK
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6
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Willauer AR, Palumbo CT, Scopelliti R, Zivkovic I, Douair I, Maron L, Mazzanti M. Stabilization of the Oxidation State +IV in Siloxide‐Supported Terbium Compounds. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201914733] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Aurélien R. Willauer
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Chad T. Palumbo
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Rosario Scopelliti
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Ivica Zivkovic
- Laboratory for Quantum MagnetismInstitute of PhysicsEPFL 1015 Lausanne Switzerland
| | - Iskander Douair
- Laboratoire de Physique et Chimie des Nano-objetsInstitut National des Sciences Appliquées 31077 Toulouse, Cedex 4 France
| | - Laurent Maron
- Laboratoire de Physique et Chimie des Nano-objetsInstitut National des Sciences Appliquées 31077 Toulouse, Cedex 4 France
| | - Marinella Mazzanti
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
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7
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Willauer AR, Palumbo CT, Scopelliti R, Zivkovic I, Douair I, Maron L, Mazzanti M. Stabilization of the Oxidation State +IV in Siloxide‐Supported Terbium Compounds. Angew Chem Int Ed Engl 2020; 59:3549-3553. [DOI: 10.1002/anie.201914733] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Indexed: 11/11/2022]
Affiliation(s)
- Aurélien R. Willauer
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Chad T. Palumbo
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Rosario Scopelliti
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Ivica Zivkovic
- Laboratory for Quantum MagnetismInstitute of PhysicsEPFL 1015 Lausanne Switzerland
| | - Iskander Douair
- Laboratoire de Physique et Chimie des Nano-objetsInstitut National des Sciences Appliquées 31077 Toulouse, Cedex 4 France
| | - Laurent Maron
- Laboratoire de Physique et Chimie des Nano-objetsInstitut National des Sciences Appliquées 31077 Toulouse, Cedex 4 France
| | - Marinella Mazzanti
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
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8
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Arnett CH, Kaiser JT, Agapie T. Remote Ligand Modifications Tune Electronic Distribution and Reactivity in Site-Differentiated, High-Spin Iron Clusters: Flipping Scaling Relationships. Inorg Chem 2019; 58:15971-15982. [PMID: 31738534 DOI: 10.1021/acs.inorgchem.9b02470] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report the synthesis, characterization, and reactivity of [LFe3O(RArIm)3Fe][OTf]2, the first Hammett series of a site-differentiated cluster. The cluster reduction potentials and CO stretching frequencies shift as expected on the basis of the electronic properties of the ligand: electron-donating substituents result in more reducing clusters and weaker C-O bonds. However, unusual trends in the energetics of their two sequential CO binding events with the substituent σp parameters are observed. Specifically, introduction of electron-donating substituents suppresses the first CO binding event (ΔΔH by as much as 7.9 kcal mol-1) but enhances the second (ΔΔH by as much as 1.9 kcal mol-1). X-ray crystallography, including multiple-wavelength anomalous diffraction, Mössbauer spectroscopy, and SQUID magnetometry, reveal that these substituent effects result from changes in the energetic penalty associated with electronic redistribution within the cluster, which occurs during the CO binding event.
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Affiliation(s)
- Charles H Arnett
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
| | - Jens T Kaiser
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
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9
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McGale J, Cutsail GE, Joseph C, Rose MJ, DeBeer S. Spectroscopic X-ray and Mössbauer Characterization of M 6 and M 5 Iron(Molybdenum)-Carbonyl Carbide Clusters: High Carbide-Iron Covalency Enhances Local Iron Site Electron Density Despite Cluster Oxidation. Inorg Chem 2019; 58:12918-12932. [PMID: 31553598 PMCID: PMC6784818 DOI: 10.1021/acs.inorgchem.9b01870] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The present study
employs a suite of spectroscopic techniques to
evaluate the electronic and bonding characteristics of the interstitial
carbide in a set of iron-carbonyl-carbide clusters, one of which is
substituted with a molybdenum atom. The M6C and M5C clusters are the dianions (Et4N)2[Fe6(μ6-C)(μ2-CO)2(CO)14] (1),
[K(benzo-18-crown-6)]2[Fe5(μ5-C)(μ2-CO)1(CO)13] (2), and [K(benzo-18-crown-6)]2[Fe5Mo(μ6-C)(μ2-CO)2(CO)15] (3). Because 1 and 2 have the same overall cluster charge (2−) but different numbers
of iron sites (1: 6 sites → 2: 5
sites), the metal atoms of 2 are formally oxidized compared
to those in 1. Despite this, Mössbauer studies
indicate that the iron sites in 2 possess significantly
greater electron density (lower spectroscopic oxidation state)
compared with those in 1. Iron K-edge X-ray absorption
and valence-to-core X-ray emission spectroscopy measurements, paired
with density functional theory spectral calculations, revealed the
presence of significant metal-to-metal and carbide 2p-based character
in the filled valence and low-lying unfilled electronic manifolds.
In all of the above experiments, the presence of the molybdenum atom
in 3 (Fe5Mo) results in somewhat unremarkable
spectroscopic properties that are essentially a “hybrid”
of 1 (Fe6) and 2 (Fe5). The overall electronic portrait that emerges illustrates that
the central inorganic carbide ligand is essential for distributing
charge and maximizing electronic communication throughout the cluster.
It is evident that the carbide coordination environment is quite flexible
and adaptive: it can drastically modify the covalency of individual
Fe–C bonds based on local structural changes and redox manipulation
of the clusters. In light of these findings, our data and calculations
suggest a potential role for the central carbon atom in FeMoco, which
likely performs a similar function in order to maintain cluster integrity
through multiple redox and ligand binding events. An in-depth
spectroscopic investigation of a series of iron-carbonyl
carbide complexes: [Fe6C] (1), [Fe5C] (2), and [Fe5CMo] (3) is
described. Using Mössbauer spectroscopy, valence-to-core X-ray
emission spectroscopy, and high-energy-resolution fluorescence-detected
X-ray absorption spectroscopy, we detail the ability of the conserved
central carbon atom in maintaining cluster stability despite dramatic
geometric rearrangements. Our study suggests a potential role for
the interstitial carbide in FeMoco as an electronic modulator, allowing
for charge and ligand accumulation under turnover conditions.
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Affiliation(s)
- Jeremy McGale
- Department of Inorganic Spectroscopy , Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36 , D-45470 , Mülheim an der Ruhr , Germany
| | - George E Cutsail
- Department of Inorganic Spectroscopy , Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36 , D-45470 , Mülheim an der Ruhr , Germany
| | - Chris Joseph
- Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Michael J Rose
- Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States
| | - Serena DeBeer
- Department of Inorganic Spectroscopy , Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36 , D-45470 , Mülheim an der Ruhr , Germany
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10
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Confer AM, Sabuncu S, Siegler MA, Moënne-Loccoz P, Goldberg DP. Mononuclear, Nonheme, High-Spin {FeNO} 7/8 Complexes Supported by a Sterically Encumbered N 4S-Thioether Ligand. Inorg Chem 2019; 58:9576-9580. [PMID: 31328501 DOI: 10.1021/acs.inorgchem.9b01475] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The synthesis of a new nonheme iron NO binding complex, [FeII(CH3CN)(N3Py2PhSEtCN)](BF4)2 (1), is reported. Complex 1, which contains two sterically encumbering phenyl substituents, exhibits a high-spin (hs) FeII (S = 2) ground state in contrast to the S = 0 ground state for unsubstituted [FeII(CH3CN)(N3PySEtCN)(BF4)2. Reaction of 1 with NO(g) in CH3CN yields an {FeNO}7 (S = 3/2) complex 2, which slowly decays at 25 °C with loss of NO• to regenerate 1. One-electron reduction of 2 with Cr(C6H6)2 at -40 °C yields the metastable, S = 1 {FeNO}8 complex 3. The nitrosyl moieties in thioether-ligated 2 and 3 are significantly less activated than in thiolate-ligated [Fe(NO)(N3PyS)]+/0, a structurally analogous pair of hs {FeNO}7/8 complexes. Calculations reveal that reduction of 2 is iron-centered, which may be a general property of hs {FeNO}7/8 complexes.
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Affiliation(s)
- Alex M Confer
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Sinan Sabuncu
- Department of Biochemistry & Molecular Biology , Oregon Health & Science University , Portland , Oregon 97239 , United States
| | - Maxime A Siegler
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Pierre Moënne-Loccoz
- Department of Biochemistry & Molecular Biology , Oregon Health & Science University , Portland , Oregon 97239 , United States
| | - David P Goldberg
- Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States
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11
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Lee HB, Shiau AA, Oyala PH, Marchiori DA, Gul S, Chatterjee R, Yano J, Britt RD, Agapie T. Tetranuclear [Mn IIIMn 3IVO 4] Complexes as Spectroscopic Models of the S 2 State of the Oxygen Evolving Complex in Photosystem II. J Am Chem Soc 2018; 140:17175-17187. [PMID: 30407806 DOI: 10.1021/jacs.8b09961] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Despite extensive biochemical, spectroscopic, and computational studies, the mechanism of biological water oxidation by the oxygen evolving complex (OEC) of Photosystem II remains a subject of significant debate. Mechanistic proposals are guided by the characterization of reaction intermediates such as the S2 state, which features two characteristic EPR signals at g = 2 and g = 4.1. Two nearly isoenergetic structural isomers have been proposed as the source of these distinct signals, but relevant structure-electronic structure studies remain rare. Herein, we report the synthesis, crystal structure, electrochemistry, XAS, magnetic susceptibility, variable temperature CW-EPR, and pulse EPR data for a series of [MnIIIMn3IVO4] cuboidal complexes as spectroscopic models of the S2 state of the OEC. Resembling the oxidation state and EPR spectra of the S2 state of the OEC, these model complexes show two EPR signals, a broad low field signal and a multiline signal, that are remarkably similar to the biological system. The effect of systematic changes in the nature of the bridging ligands on spectroscopy were studied. Results show that the electronic structure of tetranuclear Mn complexes is highly sensitive to even small geometric changes and the nature of the bridging ligands. Our model studies suggest that the spectroscopic properties of the OEC may also react very sensitively to small changes in structure; the effect of protonation state and other reorganization processes need to be carefully assessed.
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Affiliation(s)
- Heui Beom Lee
- Department of Chemistry and Chemical Engineering , California Institute of Technology , 1200 E California Blvd MC 127-72 , Pasadena , California 91125 , United States
| | - Angela A Shiau
- Department of Chemistry and Chemical Engineering , California Institute of Technology , 1200 E California Blvd MC 127-72 , Pasadena , California 91125 , United States
| | - Paul H Oyala
- Department of Chemistry and Chemical Engineering , California Institute of Technology , 1200 E California Blvd MC 127-72 , Pasadena , California 91125 , United States
| | - David A Marchiori
- Department of Chemistry , University of California Davis , One Shields Avenue , Davis , California 95616 , United States
| | - Sheraz Gul
- Molecular Biophysics and Integrated Bioimaging Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Ruchira Chatterjee
- Molecular Biophysics and Integrated Bioimaging Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Junko Yano
- Molecular Biophysics and Integrated Bioimaging Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - R David Britt
- Department of Chemistry , University of California Davis , One Shields Avenue , Davis , California 95616 , United States
| | - Theodor Agapie
- Department of Chemistry and Chemical Engineering , California Institute of Technology , 1200 E California Blvd MC 127-72 , Pasadena , California 91125 , United States
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12
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Reed CJ, Agapie T. Thermodynamics of Proton and Electron Transfer in Tetranuclear Clusters with Mn-OH 2/OH Motifs Relevant to H 2O Activation by the Oxygen Evolving Complex in Photosystem II. J Am Chem Soc 2018; 140:10900-10908. [PMID: 30064207 DOI: 10.1021/jacs.8b06426] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We report the synthesis of site-differentiated heterometallic clusters with three Fe centers and a single Mn site that binds water and hydroxide in multiple cluster oxidation states. Deprotonation of FeIII/II3MnII-OH2 clusters leads to internal reorganization resulting in formal oxidation at Mn to generate FeIII/II3MnIII-OH. 57Fe Mössbauer spectroscopy reveals that oxidation state changes (three for FeIII/II3Mn-OH2 and four for FeIII/II3Mn-OH clusters) occur exclusively at the Fe centers; the Mn center is formally MnII when water is bound and MnIII when hydroxide is bound. Experimentally determined p Ka (17.4) of the [FeIII2FeIIMnII-OH2] cluster and the reduction potentials of the [Fe3Mn-OH2] and [Fe3Mn-OH] clusters were used to analyze the O-H bond dissociation enthalpies (BDEO-H) for multiple cluster oxidation states. BDEO-H increases from 69 to 78 and 85 kcal/mol for the [FeIIIFeII2MnII-OH2], [FeIII2FeIIMnII-OH2], and [FeIII3MnII-OH2] clusters, respectively. Further insight of the proton and electron transfer thermodynamics of the [Fe3Mn-OH x] system was obtained by constructing a potential-p Ka diagram; the shift in reduction potentials of the [Fe3Mn-OH x] clusters in the presence of different bases supports the BDEO-H values reported for the [Fe3Mn-OH2] clusters. A lower limit of the p Ka for the hydroxide ligand of the [Fe3Mn-OH] clusters was estimated for two oxidation states. These data suggest BDEO-H values for the [FeIII2FeIIMnIII-OH] and [FeIII3MnIII-OH] clusters are greater than 93 and 103 kcal/mol, which hints to the high reactivity expected of the resulting [Fe3Mn═O] in this and related multinuclear systems.
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Affiliation(s)
- Christopher J Reed
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , United States
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13
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Li F, Meyer RL, Carpenter SH, VanGelder LE, Nichols AW, Machan CW, Neidig ML, Matson EM. Nitric oxide activation facilitated by cooperative multimetallic electron transfer within an iron-functionalized polyoxovanadate-alkoxide cluster. Chem Sci 2018; 9:6379-6389. [PMID: 30310566 PMCID: PMC6115649 DOI: 10.1039/c8sc00987b] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 06/30/2018] [Indexed: 01/06/2023] Open
Abstract
Cooperative multimetallic electron transfer to accommodate substrate binding.
A series of NO-bound, iron-functionalized polyoxovanadate–alkoxide (FePOV–alkoxide) clusters have been synthesized, providing insight into the role of multimetallic constructs in the coordination and activation of a substrate. Upon exposure of the heterometallic cluster to NO, the vanadium-oxide metalloligand is oxidized by a single electron, shuttling the reducing equivalent to the {FeNO} subunit to form a {FeNO}7 species. Four NO-bound clusters with electronic distributions ranging from [VV3VIV2]{FeNO}7 to [VIV5]{FeNO}7 have been synthesized, and characterized via1H NMR, infrared, and electronic absorption spectroscopies. The ability of the FePOV–alkoxide cluster to store reducing equivalents in the metalloligand for substrate coordination and activation highlights the ultility of the metal-oxide scaffold as a redox reservoir.
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Affiliation(s)
- F Li
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA .
| | - R L Meyer
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA .
| | - S H Carpenter
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA .
| | - L E VanGelder
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA .
| | - A W Nichols
- Department of Chemistry , University of Virginia , Charlottesville , Virginia 22904-4319 , USA
| | - C W Machan
- Department of Chemistry , University of Virginia , Charlottesville , Virginia 22904-4319 , USA
| | - M L Neidig
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA .
| | - E M Matson
- Department of Chemistry , University of Rochester , Rochester , New York 14627 , USA .
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14
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Arnett CH, Chalkley MJ, Agapie T. A Thermodynamic Model for Redox-Dependent Binding of Carbon Monoxide at Site-Differentiated, High Spin Iron Clusters. J Am Chem Soc 2018; 140:5569-5578. [PMID: 29589921 PMCID: PMC6452638 DOI: 10.1021/jacs.8b01825] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Binding of N2 and CO by the FeMo-cofactor of nitrogenase depends on the redox level of the cluster, but the extent to which pure redox chemistry perturbs the affinity of high spin iron clusters for π-acids is not well understood. Here, we report a series of site-differentiated iron clusters that reversibly bind CO in redox states FeII4 through FeIIFeIII3. One electron redox events result in small changes in the affinity for (at most ∼400-fold) and activation of CO (at most 28 cm-1 for νCO). The small influence of redox chemistry on the affinity of these high spin, valence-localized clusters for CO is in stark contrast to the large enhancements (105-1022 fold) in π-acid affinity reported for monometallic and low spin, bimetallic iron complexes, where redox chemistry occurs exclusively at the ligand binding site. While electron-loading at metal centers remote from the substrate binding site has minimal influence on the CO binding energetics (∼1 kcal·mol-1), it provides a conduit for CO binding at an FeIII center. Indeed, internal electron transfer from these remote sites accommodates binding of CO at an FeIII, with a small energetic penalty arising from redox reorganization (∼2.6 kcal·mol-1). The ease with which these clusters redistribute electrons in response to ligand binding highlights a potential pathway for coordination of N2 and CO by FeMoco, which may occur on an oxidized edge of the cofactor.
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Affiliation(s)
- Charles H. Arnett
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Matthew J. Chalkley
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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