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Montgomery CL, Amtawong J, Jordan AM, Kurtz DA, Dempsey JL. Proton transfer kinetics of transition metal hydride complexes and implications for fuel-forming reactions. Chem Soc Rev 2023; 52:7137-7169. [PMID: 37750006 DOI: 10.1039/d3cs00355h] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/27/2023]
Abstract
Proton transfer reactions involving transition metal hydride complexes are prevalent in a number of catalytic fuel-forming reactions, where the proton transfer kinetics to or from the metal center can have significant impacts on the efficiency, selectivity, and stability associated with the catalytic cycle. This review correlates the often slow proton transfer rate constants of transition metal hydride complexes to their electronic and structural descriptors and provides perspective on how to exploit these parameters to control proton transfer kinetics to and from the metal center. A toolbox of techniques for experimental determination of proton transfer rate constants is discussed, and case studies where proton transfer rate constant determination informs fuel-forming reactions are highlighted. Opportunities for extending proton transfer kinetic measurements to additional systems are presented, and the importance of synergizing the thermodynamics and kinetics of proton transfer involving transition metal hydride complexes is emphasized.
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Affiliation(s)
- Charlotte L Montgomery
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Jaruwan Amtawong
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Aldo M Jordan
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Daniel A Kurtz
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Jillian L Dempsey
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
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2
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Affiliation(s)
- Oliver Einsle
- Institute for Biochemistry, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Douglas C. Rees
- Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, California Institute of Technology, Pasadena California 91125, United States
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3
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Morrison CN, Spatzal T, Rees DC. Reversible Protonated Resting State of the Nitrogenase Active Site. J Am Chem Soc 2017; 139:10856-10862. [PMID: 28692802 PMCID: PMC5553094 DOI: 10.1021/jacs.7b05695] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Protonated states of the nitrogenase
active site are mechanistically
significant since substrate reduction is invariably accompanied by
proton uptake. We report the low pH characterization by X-ray crystallography
and EPR spectroscopy of the nitrogenase molybdenum iron (MoFe) proteins
from two phylogenetically distinct nitrogenases (Azotobacter
vinelandii, Av, and Clostridium pasteurianum, Cp) at pHs between 4.5 and 8. X-ray data at pHs of 4.5–6
reveal the repositioning of side chains along one side of the FeMo-cofactor,
and the corresponding EPR data shows a new S = 3/2
spin system with spectral features similar to a state previously observed
during catalytic turnover. The structural changes suggest that FeMo-cofactor
belt sulfurs S3A or S5A are potential protonation sites. Notably,
the observed structural and electronic low pH changes are correlated
and reversible. The detailed structural rearrangements differ between
the two MoFe proteins, which may reflect differences in potential
protonation sites at the active site among nitrogenase species. These
observations emphasize the benefits of investigating multiple nitrogenase
species. Our experimental data suggest that reversible protonation
of the resting state is likely occurring, and we term this state “E0H+”, following the Lowe–Thorneley
naming scheme.
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Affiliation(s)
- Christine N Morrison
- Division of Chemistry and Chemical Engineering and ‡Howard Hughes Medical Institute, California Institute of Technology , Pasadena, California 91125, United States
| | - Thomas Spatzal
- Division of Chemistry and Chemical Engineering and ‡Howard Hughes Medical Institute, California Institute of Technology , Pasadena, California 91125, United States
| | - Douglas C Rees
- Division of Chemistry and Chemical Engineering and ‡Howard Hughes Medical Institute, California Institute of Technology , Pasadena, California 91125, United States
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4
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Bergner M, Roy L, Dechert S, Neese F, Ye S, Meyer F. Ligand Rearrangements at Fe/S Cofactors: Slow Isomerization of a Biomimetic [2Fe-2S] Cluster. Angew Chem Int Ed Engl 2017; 56:4882-4886. [DOI: 10.1002/anie.201612621] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Indexed: 02/01/2023]
Affiliation(s)
- Marie Bergner
- Universität Göttingen; Institut für Anorganische Chemie; Tammannstrasse 4 37077 Göttingen Germany
| | - Lisa Roy
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstrasse 34-36 45470 Mülheim an der Ruhr Germany
| | - Sebastian Dechert
- Universität Göttingen; Institut für Anorganische Chemie; Tammannstrasse 4 37077 Göttingen Germany
| | - Frank Neese
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstrasse 34-36 45470 Mülheim an der Ruhr Germany
| | - Shengfa Ye
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstrasse 34-36 45470 Mülheim an der Ruhr Germany
| | - Franc Meyer
- Universität Göttingen; Institut für Anorganische Chemie; Tammannstrasse 4 37077 Göttingen Germany
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5
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Bergner M, Roy L, Dechert S, Neese F, Ye S, Meyer F. Ligandenumlagerungen an Fe/S-Cofaktoren: langsame Isomerisierung eines biomimetischen [2Fe-2S]-Clusters. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201612621] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Marie Bergner
- Universität Göttingen; Institut für Anorganische Chemie; Tammannstraße 4 37077 Göttingen Deutschland
| | - Lisa Roy
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstraße 34-36 45470 Mülheim an der Ruhr Deutschland
| | - Sebastian Dechert
- Universität Göttingen; Institut für Anorganische Chemie; Tammannstraße 4 37077 Göttingen Deutschland
| | - Frank Neese
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstraße 34-36 45470 Mülheim an der Ruhr Deutschland
| | - Shengfa Ye
- Max-Planck-Institut für Chemische Energiekonversion; Stiftstraße 34-36 45470 Mülheim an der Ruhr Deutschland
| | - Franc Meyer
- Universität Göttingen; Institut für Anorganische Chemie; Tammannstraße 4 37077 Göttingen Deutschland
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6
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Al-Rammahi TMM, Henderson RA. Exploring the acid-catalyzed substitution mechanism of [Fe4S4Cl4]2−. Dalton Trans 2016; 45:307-14. [DOI: 10.1039/c5dt04008f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Kinetic studies focussing on either the protonation or substitution step of the acid catalyzed substitution reactions of [Fe4S4Cl4]2− support a mechanism involving concomitant cluster protonation and Fe–(μ3-SH) bond cleavage.
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7
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Alwaaly A, Dance I, Henderson RA. Unexpected explanation for the enigmatic acid-catalysed reactivity of [Fe4S4X4](2-) clusters. Chem Commun (Camb) 2015; 50:4799-802. [PMID: 24637735 DOI: 10.1039/c4cc00922c] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Density functional calculations show that Fe-S clusters undergo unexpected large structural changes when protonated at S. Protonation of prototypical cubanoid [Fe4S4X4](2-) to [Fe4S3(SH)X4](-) (X = Cl, SR, OR) results in formation of doubly-bridging SH, severance of one Fe-S bond, and creation of a three-coordinate Fe. These findings explain previously enigmatic results concerning the reactivity of these clusters, including the rates of protonation, pKa data, and the kinetics of acid-catalysed ligand substitution.
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Affiliation(s)
- Ahmed Alwaaly
- School of Chemistry, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
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Dance I, Henderson RA. Large structural changes upon protonation of Fe4S4 clusters: the consequences for reactivity. Dalton Trans 2014; 43:16213-26. [DOI: 10.1039/c4dt01687d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recognition that protonation of μ3-S in [Fe4S4X4]2− clusters causes breaking of an S–Fe bond provides a kinetically consistent general mechanism for the acid-catalysed substitution reactions of [Fe4S4X4]2− clusters.
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Affiliation(s)
- Ian Dance
- School of Chemistry
- University of New South Wales
- Sydney 2052, Australia
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Saouma CT, Kaminsky W, Mayer JM. Protonation and concerted proton-electron transfer reactivity of a bis-benzimidazolate ligated [2Fe-2S] model for Rieske clusters. J Am Chem Soc 2012; 134:7293-6. [PMID: 22519585 DOI: 10.1021/ja3019324] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A model system for biological Rieske clusters that incorporates bis-benzimidazolate ligands ((Pr)bbim)(2-) has been developed ((Pr)bbimH(2) = 4,4-bis(benzimidazol-2-yl)heptane). The diferric and mixed-valence clusters have been prepared and characterized in both their protonated and deprotonated states. The thermochemistry of interconversions of these species has been measured, and the effect of protonation on the reduction potential is in good agreement to that observed in the biological systems. The mixed-valence and protonated congener [Fe(2)S(2)((Pr)bbim)((Pr)bbimH)](Et(4)N)(2) (4) reacts rapidly with TEMPO or p-benzoquinones to generate diferric and deprotonated [Fe(2)S(2)((Pr)bbim)(2)](Et(4)N)(2) (1) and 1 equiv of TEMPOH or 0.5 equiv of p-benzohydroquinones, respectively. The reaction with TEMPO is the first well-defined example of concerted proton-electron transfer (CPET) at a synthetic ferric/ferrous [Fe-S] cluster.
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Affiliation(s)
- Caroline T Saouma
- Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA
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Garrett B, Henderson RA. Protonation and substitution reactions of [{WFe₃S₄Cl₃}₂(μ-L)₃]³⁻ (L = SEt or OMe): quantifying how metal content and spectator ligands individually affect reactivity. Dalton Trans 2010; 39:4586-92. [PMID: 20386803 DOI: 10.1039/b925835c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Kinetic studies on the substitution reactions of the terminal chloro-ligands of [{WFe₃S₄Cl₃}₂(μ-L)₃]³⁻ (L = SEt or MeO) by PhS⁻ in the presence of [NHEt₃](+) or [pyrH](+) allow determination of the proton affinities and rates of PhS⁻ and proton binding to the clusters. The behaviours of both clusters are similar and follow the same general kinetic characteristics established in earlier work for other synthetic Fe-S-based clusters. Comparison of the results obtained with [{WFe₃S₄Cl₃}₂(μ-SEt)₃]³⁻ with those of the isostructural [{MoFe₃S₄Cl₃}₂(μ-SEt)₃]³⁻ shows that changing a Mo for W in the cuboidal cluster framework has a large effect on the rates of binding of PhS⁻ or a proton. In contrast, comparison of the results of [{WFe₃S₄Cl₃}₂(μ-SEt)₃]³⁻ with those of [{WFe₃S₄Cl₃}₂(μ-OMe)₃]³⁻ shows that changing the bridging ligands has only a small effect on the rates of binding of PhS⁻ or a proton. The reactivities of [{MFe₃S₄Cl₃}₂(μ-L)₃]³⁻ are inconsistent with the major influence of the metal or bridging ligands being electronic, and are more consistent with their modulating the ability of the cluster to undergo bond length reorganisation during binding of the nucleophile or proton.
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Affiliation(s)
- Brendan Garrett
- School of Chemistry, Newcastle University, Newcastle upon Tyne, UK
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11
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Dunford AJ, Henderson RA. Kinetics and mechanism of the acid-catalyzed substitution reactions of [Fe6S9(SEt)2]4−. J COORD CHEM 2010. [DOI: 10.1080/00958971003671819] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Adrian J. Dunford
- a School of Chemistry, Newcastle University , Newcastle upon Tyne, NE1 7RU, UK
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Algarra AG, Basallote MG, Fernandez-Trujillo MJ, Llusar R, Pino-Chamorro JA, Sorribes I, Vicent C. Site specific ligand substitution in cubane-type Mo3FeS44+ clusters: Kinetics and mechanism of reaction and isolation of mixed ligand Cl/SPh complexes. Dalton Trans 2010; 39:3725-35. [DOI: 10.1039/b924801c] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Bates K, Henderson RA. Binding nucleophiles to [Fe4Y4Cl4](2-) (Y = S or Se) can increase or suppress the rate of proton transfer to the cluster. Inorg Chem 2008; 47:5850-8. [PMID: 18540596 DOI: 10.1021/ic800142e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the proton transfer reactions between [Fe 4Y 4Cl 4] (2-) (Y = S or Se) and [pyrH] (+) (pyr = pyrrolidine) in the presence of a variety of nucleophiles (L = I (-), Br (-), PhS (-), EtS (-) or ButNC), initial binding of the nucleophile can occur to generate [Fe 4Y 4Cl 4(L)] ( n- ). The subsequent rate of proton transfer depends markedly on the nature of L. Stopped-flow kinetic studies show that proton transfer from [pyrH] (+) to [Fe 4Y 4Cl 4] (2-) { (S) k 4 = (2.1 +/- 0.5) x 10 (4) dm (3) mol (-1) s (-1); (Se) k 4 = (8.0 +/- 0.5) x 10 (3) dm (3) mol (-1) s (-1)} is increased by prior binding of L = PhS (-) or Bu ( t )NC to form [Fe 4Y 4Cl 4(L)] (n-) ( (S) k 7 (L) approximately 1 x 10 (6) dm (3) mol (-1) s (-1)), but prior binding of L = I (-), Br (-), or EtS (-) to the clusters inhibits the rate of proton transfer {e.g. (S) k 7 (I) = (6.0 +/- 0.8) x 10 (2) dm (3) mol (-1) s (-1); (Se) k 7 (I) = (4.5 +/- 0.5) x 10 (2) dm (3) mol (-1) s (-1)}. This behavior is correlated with the bonding characteristics of L and the effect this has on bond length reorganization within the cluster upon proton transfer.
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Affiliation(s)
- Katie Bates
- Chemistry, School of Natural Sciences, Newcastle University, Newcastle upon Tyne, UK
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