1
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Rice DB, Wong D, Weyhermüller T, Neese F, DeBeer S. The spin-forbidden transition in iron(IV)-oxo catalysts relevant to two-state reactivity. SCIENCE ADVANCES 2024; 10:eado1603. [PMID: 38941457 PMCID: PMC11212722 DOI: 10.1126/sciadv.ado1603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2024] [Accepted: 05/23/2024] [Indexed: 06/30/2024]
Abstract
Quintet oxoiron(IV) intermediates are often invoked in nonheme iron enzymes capable of performing selective oxidation, while most well-characterized synthetic model oxoiron(IV) complexes have a triplet ground state. These differing spin states lead to the proposal of a two-state reactivity model, where the complexes cross from the triplet to an excited quintet state. However, the energy of this quintet state has never been measured experimentally. Here, magnetic circular dichroism is used to assign the singlet and triplet excited states in a series of triplet oxoiron(IV) complexes. These transition energies are used to determine the energies of the quintet state via constrained fitting of 2p3d resonant inelastic x-ray scattering. This allowed for a direct correlation between the quintet energies and substrate C─H oxidation rates.
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Affiliation(s)
- Derek B. Rice
- Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany
| | - Deniz Wong
- Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
| | - Thomas Weyhermüller
- Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung, D-45470 Mülheim an der Ruhr, Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany
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2
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Barman SK, Yang MY, Parsell TH, Green MT, Borovik AS. Semiempirical method for examining asynchronicity in metal-oxido-mediated C-H bond activation. Proc Natl Acad Sci U S A 2021; 118:e2108648118. [PMID: 34465626 PMCID: PMC8433561 DOI: 10.1073/pnas.2108648118] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The oxidation of substrates via the cleavage of thermodynamically strong C-H bonds is an essential part of mammalian metabolism. These reactions are predominantly carried out by enzymes that produce high-valent metal-oxido species, which are directly responsible for cleaving the C-H bonds. While much is known about the identity of these transient intermediates, the mechanistic factors that enable metal-oxido species to accomplish such difficult reactions are still incomplete. For synthetic metal-oxido species, C-H bond cleavage is often mechanistically described as synchronous, proton-coupled electron transfer (PCET). However, data have emerged that suggest that the basicity of the M-oxido unit is the key determinant in achieving enzymatic function, thus requiring alternative mechanisms whereby proton transfer (PT) has a more dominant role than electron transfer (ET). To bridge this knowledge gap, the reactivity of a monomeric MnIV-oxido complex with a series of external substrates was studied, resulting in a spread of over 104 in their second-order rate constants that tracked with the acidity of the C-H bonds. Mechanisms that included either synchronous PCET or rate-limiting PT, followed by ET, did not explain our results, which led to a proposed PCET mechanism with asynchronous transition states that are dominated by PT. To support this premise, we report a semiempirical free energy analysis that can predict the relative contributions of PT and ET for a given set of substrates. These findings underscore why the basicity of M-oxido units needs to be considered in C-H functionalization.
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Affiliation(s)
- Suman K Barman
- Department of Chemistry, University of California Irvine, CA 92697;
| | - Meng-Yin Yang
- Department of Chemistry, University of California Irvine, CA 92697
| | | | - Michael T Green
- Department of Chemistry, University of California Irvine, CA 92697;
- Department of Molecular Biosciences and Biochemistry, University of California Irvine, CA 92697
| | - A S Borovik
- Department of Chemistry, University of California Irvine, CA 92697;
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3
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Brewer SM, Schwartz TM, Mekhail MA, Turan LS, Prior TJ, Hubin TJ, Janesko BG, Green KN. Mechanistic Insights into Iron-Catalyzed C–H Bond Activation and C–C Coupling. Organometallics 2021; 40:2467-2477. [DOI: 10.1021/acs.organomet.1c00211] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Samantha M. Brewer
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, Texas 76129, United States
| | - Timothy M. Schwartz
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, Texas 76129, United States
| | - Magy A. Mekhail
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, Texas 76129, United States
| | - Lara S. Turan
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, Texas 76129, United States
| | - Timothy J. Prior
- Department of Chemistry and Biochemistry, University of Hull, Hull HU6 7RX, U.K
| | - Timothy J. Hubin
- Department of Chemistry and Physics, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, Oklahoma 73096, United States
| | - Benjamin G. Janesko
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, Texas 76129, United States
| | - Kayla N. Green
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, Texas 76129, United States
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4
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Mukherjee G, Satpathy JK, Bagha UK, Mubarak MQE, Sastri CV, de Visser SP. Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants. ACS Catal 2021. [DOI: 10.1021/acscatal.1c01993] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Gourab Mukherjee
- Department of Chemistry, Indian Institute of Technology Guwahati, 781039, Assam, India
| | - Jagnyesh K. Satpathy
- Department of Chemistry, Indian Institute of Technology Guwahati, 781039, Assam, India
| | - Umesh K. Bagha
- Department of Chemistry, Indian Institute of Technology Guwahati, 781039, Assam, India
| | - M. Qadri E. Mubarak
- Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
- Fakulti Sains dan Teknologi, Universiti Sains Islam Malaysia, Bandar Baru Nilai, 71800 Nilai, Negeri Sembilan Malaysia
| | - Chivukula V. Sastri
- Department of Chemistry, Indian Institute of Technology Guwahati, 781039, Assam, India
| | - Sam P. de Visser
- Department of Chemistry, Indian Institute of Technology Guwahati, 781039, Assam, India
- Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
- Department of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
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5
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Tripodi GL, Dekker MMJ, Roithová J, Que L. Tuning the H-Atom Transfer Reactivity of Iron(IV)-Oxo Complexes as Probed by Infrared Photodissociation Spectroscopy. Angew Chem Int Ed Engl 2021; 60:7126-7131. [PMID: 33393186 PMCID: PMC8048595 DOI: 10.1002/anie.202016695] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Indexed: 01/14/2023]
Abstract
Reactivities of non-heme iron(IV)-oxo complexes are mostly controlled by the ligands. Complexes with tetradentate ligands such as [(TPA)FeO]2+ (TPA=tris(2-pyridylmethyl)amine) belong to the most reactive ones. Here, we show a fine-tuning of the reactivity of [(TPA)FeO]2+ by an additional ligand X (X=CH3 CN, CF3 SO3- , ArI, and ArIO; ArI=2-(t BuSO2 )C6 H4 I) attached in solution and reveal a thus far unknown role of the ArIO oxidant. The HAT reactivity of [(TPA)FeO(X)]+/2+ decreases in the order of X: ArIO > MeCN > ArI ≈ TfO- . Hence, ArIO is not just a mere oxidant of the iron(II) complex, but it can also increase the reactivity of the iron(IV)-oxo complex as a labile ligand. The detected HAT reactivities of the [(TPA)FeO(X)]+/2+ complexes correlate with the Fe=O and FeO-H stretching vibrations of the reactants and the respective products as determined by infrared photodissociation spectroscopy. Hence, the most reactive [(TPA)FeO(ArIO)]2+ adduct in the series has the weakest Fe=O bond and forms the strongest FeO-H bond in the HAT reaction.
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Affiliation(s)
- Guilherme L. Tripodi
- Department of spectroscopy and CatalysisInstitute for Molecules and MaterialsRadboud University NijmegenHeyendaalseweg 1356525AJNijmegenThe Netherlands
| | - Magda M. J. Dekker
- Department of spectroscopy and CatalysisInstitute for Molecules and MaterialsRadboud University NijmegenHeyendaalseweg 1356525AJNijmegenThe Netherlands
| | - Jana Roithová
- Department of spectroscopy and CatalysisInstitute for Molecules and MaterialsRadboud University NijmegenHeyendaalseweg 1356525AJNijmegenThe Netherlands
| | - Lawrence Que
- Department of ChemistryUniversity of MinnesotaMinneapolisTwin Cities 207 Pleasant Street SE55455MNUSA
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6
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Tripodi GL, Dekker MMJ, Roithová J, Que L. Tuning the H‐Atom Transfer Reactivity of Iron(IV)‐Oxo Complexes as Probed by Infrared Photodissociation Spectroscopy. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202016695] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Guilherme L. Tripodi
- Department of spectroscopy and Catalysis Institute for Molecules and Materials Radboud University Nijmegen Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Magda M. J. Dekker
- Department of spectroscopy and Catalysis Institute for Molecules and Materials Radboud University Nijmegen Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Jana Roithová
- Department of spectroscopy and Catalysis Institute for Molecules and Materials Radboud University Nijmegen Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Lawrence Que
- Department of Chemistry University of Minnesota Twin Cities, 207 Pleasant Street SE Minneapolis MN 55455 USA
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7
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Wegeberg C, Skavenborg ML, Liberato A, McPherson JN, Browne WR, Hedegård ED, McKenzie CJ. Engineering the Oxidative Potency of Non-Heme Iron(IV) Oxo Complexes in Water for C-H Oxidation by a cis Donor and Variation of the Second Coordination Sphere. Inorg Chem 2021; 60:1975-1984. [PMID: 33470794 DOI: 10.1021/acs.inorgchem.0c03441] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
A series of iron(IV) oxo complexes, which differ in the donor (CH2py or CH2COO-) cis to the oxo group, three with hemilabile pendant donor/second coordination sphere base/acid arms (pyH/py or ROH), have been prepared in water at pH 2 and 7. The νFe═O values of 832 ± 2 cm-1 indicate similar FeIV═O bond strengths; however, different reactivities toward C-H substrates in water are observed. HAT occurs at rates that differ by 1 order of magnitude with nonclassical KIEs (kH/kD = 30-66) consistent with hydrogen atom tunneling. Higher KIEs correlate with faster reaction rates as well as a greater thermodynamic stability of the iron(III) resting states. A doubling in rate from pH 7 to pH 2 for substrate C-H oxidation by the most potent complex, that with a cis-carboxylate donor, [FeIVO(Htpena)]2+, is observed. Supramolecular assistance by the first and second coordination spheres in activating the substrate is proposed. The lifetime of this complex in the absence of a C-H substrate is the shortest (at pH 2, 3 h vs up to 1.3 days for the most stable complex), implying that slow water oxidation is a competing background reaction. The iron(IV)═O complex bearing an alcohol moiety in the second coordination sphere displays significantly shorter lifetimes due to a competing selective intramolecular oxidation of the ligand.
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Affiliation(s)
- Christina Wegeberg
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.,Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Mathias L Skavenborg
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.,Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, New South Wales, Australia
| | - Andrea Liberato
- Universidad de Cádiz, Facultad de Ciencias, Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Puerto Real, Cádiz 11510, Spain
| | - James N McPherson
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Wesley R Browne
- Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Erik D Hedegård
- Division of Theoretical Chemistry, Lund University, Naturvetarvägen 14, 221 00 Lund, Sweden
| | - Christine J McKenzie
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
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8
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Hofmann AJ, Niederegger L, Hess CR. Neighbouring effects on catalytic epoxidation by Fe-cyclam in M 2-PDIxCy complexes. Dalton Trans 2020; 49:17642-17648. [PMID: 33226393 DOI: 10.1039/d0dt03758c] [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
The unsymmetric PDIeCy ligand, featuring pyridinediimine and cylam sites, can be selectively metalated. Complementing the diiron compound, we have synthesized two heterobimetallic isomers, [ZnPDIFeCy(PDIeCy)(OTf)4] (3) and [FePDIZnCy(PDIeCy)(OTf)4] (4), and a dizinc complex, [Zn2(PDIeCy)(OTf)4] (5). Olefin epoxidation by the series of complexes was investigated. The M-PDI site influences the reactivity of the M-cyclam, resulting in increased activity toward enones.
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Affiliation(s)
- Andreas J Hofmann
- Technische Universität München, Department of Chemistry and Catalysis Research Center, 85747 Garching, Germany.
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9
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Affiliation(s)
- Sason Shaik
- Institute of Chemistry The Hebrew University of Jerusalem Edmond J. Safra Campus, Givat Ram Jerusalem 9090401 Israel
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10
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Park H, Lee D. Ligand Taxonomy for Bioinorganic Modeling of Dioxygen-Activating Non-Heme Iron Enzymes. Chemistry 2020; 26:5916-5926. [PMID: 31909506 DOI: 10.1002/chem.201904975] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 01/04/2020] [Indexed: 12/15/2022]
Abstract
Novel functions emerge from novel structures. To develop efficient catalytic systems for challenging chemical transformations, chemists often seek inspirations from enzymatic catalysis. A large number of iron complexes supported by nitrogen-rich multidentate ligands have thus been developed to mimic oxo-transfer reactivity of dioxygen-activating metalloenzymes. Such efforts have significantly advanced our understanding of the reaction mechanisms by trapping key intermediates and elucidating their geometric and electronic properties. Critical to the success of this biomimetic approach is the design and synthesis of elaborate ligand systems to balance the thermodynamic stability, structural adaptability, and chemical reactivity. In this Concept article, representative design strategies for biomimetic atom-transfer chemistry are discussed from the perspectives of "ligand builders". Emphasis is placed on how the primary coordination sphere is constructed, and how it can be elaborated further by rational design for desired functions.
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Affiliation(s)
- Hyunchang Park
- Department of Chemistry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Korea
| | - Dongwhan Lee
- Department of Chemistry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Korea
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11
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Schaefer AW, Ehudin MA, Quist DA, Tang JA, Karlin KD, Solomon EI. Spin Interconversion of Heme-Peroxo-Copper Complexes Facilitated by Intramolecular Hydrogen-Bonding Interactions. J Am Chem Soc 2019; 141:4936-4951. [PMID: 30836005 PMCID: PMC6457345 DOI: 10.1021/jacs.9b00118] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Synthetic peroxo-bridged high-spin (HS) heme-(μ-η2:η1-O22-)-Cu(L) complexes incorporating (as part of the copper ligand) intramolecular hydrogen-bond (H-bond) capabilities and/or steric effects are herein demonstrated to affect the complex's electronic and geometric structure, notably impacting the spin state. An H-bonding interaction with the peroxo core favors a low-spin (LS) heme-(μ-η1:η1-O22-)-Cu(L) structure, resulting in a reversible temperature-dependent interconversion of spin state (5 coordinate HS to 6 coordinate LS). The LS state dominates at low temperatures, even in the absence of a strong trans-axial heme ligand. Lewis base addition inhibits the H-bond facilitated spin interconversion by competition for the H-bond donor, illustrating the precise H-bonding interaction required to induce spin-crossover (SCO). Resonance Raman spectroscopy (rR) shows that the H-bonding pendant interacts with the bridging peroxide ligand to stabilize the LS but not the HS state. The H-bond (to the Cu-bound O atom) acts to weaken the O-O bond and strengthen the Fe-O bond, exhibiting ν(M-O) and ν(O-O) values comparable to analogous known LS complexes with a strong donating trans-axial ligand, 1,5-dicyclohexylimidazole, (DCHIm)heme-(μ-η1:η1-O22-)-Cu(L). Variable-temperature (-90 to -130 °C) UV-vis and 2H NMR spectroscopies confirm the SCO process and implicate the involvement of solvent binding. Examining a case of solvent binding without SCO, thermodynamic parameters were obtained from a van't Hoff analysis, accounting for its contribution in SCO. Taken together, these data provide evidence for the H-bond group facilitating a core geometry change and allowing solvent to bind, stabilizing a LS state. The rR data, complemented by DFT analysis, reveal a stronger H-bonding interaction with the peroxo core in the LS compared to the HS complexes, which enthalpically favors the LS state. These insights enhance our fundamental understanding of secondary coordination sphere influences in metalloenzymes.
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Affiliation(s)
- Andrew W. Schaefer
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Melanie A. Ehudin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David A. Quist
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Joel A. Tang
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kenneth D. Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Edward I. Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
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12
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Comba P, Faltermeier D, Gieger S, Keppler F, Schöler HF, Schroll M. Iron catalyzed demethylation of acetic acid*. J COORD CHEM 2018. [DOI: 10.1080/00958972.2018.1490414] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Peter Comba
- Anorganisch-Chemisches Institut and Interdisciplinary Center for Scientific Computing (IWR), Heidelberg University, Heidelberg, Germany
| | - Dieter Faltermeier
- Anorganisch-Chemisches Institut and Interdisciplinary Center for Scientific Computing (IWR), Heidelberg University, Heidelberg, Germany
| | - Sascha Gieger
- Institute of Earth Sciences and Heidelberg Center for the Environment (HCE), Heidelberg University, Heidelberg, Germany
| | - Frank Keppler
- Institute of Earth Sciences and Heidelberg Center for the Environment (HCE), Heidelberg University, Heidelberg, Germany
| | - Heinz Friedrich Schöler
- Institute of Earth Sciences and Heidelberg Center for the Environment (HCE), Heidelberg University, Heidelberg, Germany
| | - Moritz Schroll
- Institute of Earth Sciences and Heidelberg Center for the Environment (HCE), Heidelberg University, Heidelberg, Germany
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13
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Zemlyakova EO, Pestov AV, Slepukhin PA, Kapitanova EI, Petrova YS, Neudachina LK. N,N-Bis(2-Hydroxyethyl)taurine: Synthesis, Structure, and Stability of the Complexes with Cobalt(II) and Nickel(II). RUSS J COORD CHEM+ 2018. [DOI: 10.1134/s107032841811009x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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14
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Beyond the classical thermodynamic contributions to hydrogen atom abstraction reactivity. Proc Natl Acad Sci U S A 2018; 115:E10287-E10294. [PMID: 30254163 DOI: 10.1073/pnas.1806399115] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Hydrogen atom abstraction (HAA) reactions are cornerstones of chemistry. Various (metallo)enzymes performing the HAA catalysis evolved in nature and inspired the rational development of multiple synthetic catalysts. Still, the factors determining their catalytic efficiency are not fully understood. Herein, we define the simple thermodynamic factor η by employing two thermodynamic cycles: one for an oxidant (catalyst), along with its reduced, protonated, and hydrogenated form; and one for the substrate, along with its oxidized, deprotonated, and dehydrogenated form. It is demonstrated that η reflects the propensity of the substrate and catalyst for (a)synchronicity in concerted H+/e- transfers. As such, it significantly contributes to the activation energies of the HAA reactions, in addition to a classical thermodynamic (Bell-Evans-Polanyi) effect. In an attempt to understand the physicochemical interpretation of η, we discovered an elegant link between η and reorganization energy λ from Marcus theory. We discovered computationally that for a homologous set of HAA reactions, λ reaches its maximum for the lowest |η|, which then corresponds to the most synchronous HAA mechanism. This immediately implies that among HAA processes with the same reaction free energy, ΔG 0, the highest barrier (≡ΔG ≠) is expected for the most synchronous proton-coupled electron (i.e., hydrogen) transfer. As proof of concept, redox and acidobasic properties of nonheme FeIVO complexes are correlated with activation free energies for HAA from C-H and O-H bonds. We believe that the reported findings may represent a powerful concept in designing new HAA catalysts.
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15
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Brewer SM, Wilson KR, Jones DG, Reinheimer EW, Archibald SJ, Prior TJ, Ayala MA, Foster AL, Hubin TJ, Green KN. Increase of Direct C-C Coupling Reaction Yield by Identifying Structural and Electronic Properties of High-Spin Iron Tetra-azamacrocyclic Complexes. Inorg Chem 2018; 57:8890-8902. [PMID: 30024738 PMCID: PMC7067264 DOI: 10.1021/acs.inorgchem.8b00777] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Macrocyclic ligands have been explored extensively as scaffolds for transition metal catalysts for oxygen and hydrogen atom transfer reactions. C-C reactions facilitated using earth abundant metals bound to macrocyclic ligands have not been well-understood but could be a green alternative to replacing the current expensive and toxic precious metal systems most commonly used for these processes. Therefore, the yields from direct Suzuki-Miyaura C-C coupling of phenylboronic acid and pyrrole to produce 2-phenylpyrrole facilitated by eight high-spin iron complexes ([Fe3+L1(Cl)2]+, [Fe3+L4(Cl)2]+, [Fe2+L5(Cl)]+, [Fe2+L6(Cl)2], [Fe3+L7(Cl)2]+, [Fe3+L8(Cl)2]+, [Fe2+L9(Cl)]+, and [Fe2+L10(Cl)]+) were compared to identify the effect of structural and electronic properties on catalytic efficiency. Specifically, catalyst complexes were compared to evaluate the effect of five properties on catalyst reaction yields: (1) the coordination requirements of the catalyst, (2) redox half-potential of each complex, (3) topological constraint/rigidity, (4) N atom modification(s) increasing oxidative stability of the complex, and (5) geometric parameters. The need for two labile cis-coordination sites was confirmed based on a 42% decrease in catalytic reaction yield observed when complexes containing pentadentate ligands were used in place of complexes with tetradentate ligands. A strong correlation between iron(III/II) redox potential and catalytic reaction yields was also observed, with [Fe2+L6(Cl)2] providing the highest yield (81%, -405 mV). A Lorentzian fitting of redox potential versus yields predicts that these catalysts can undergo more fine-tuning to further increase yields. Interestingly, the remaining properties explored did not show a direct, strong relationship to catalytic reaction yields. Altogether, these results show that modifications to the ligand scaffold using fundamental concepts of inorganic coordination chemistry can be used to control the catalytic activity of macrocyclic iron complexes by controlling redox chemistry of the iron center. Furthermore, the data provide direction for the design of improved catalysts for this reaction and strategies to understand the impact of a ligand scaffold on catalytic activity of other reactions.
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Affiliation(s)
- Samantha M. Brewer
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, TX 76129, United States
| | - Kevin R. Wilson
- Department of Chemistry and Physics, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 73096, United States
| | - Donald G. Jones
- Department of Chemistry and Physics, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 73096, United States
| | - Eric W. Reinheimer
- Rigaku Oxford Diffraction, 9009 New Trails Drive The Woodlands, TX, United States
| | - Stephen J. Archibald
- Department of Chemistry and Positron Emission Tomography Research Centre, University of Hull, Cottingham Road, Hull HU6 7RX, UK
| | - Timothy J. Prior
- Department of Chemistry and Positron Emission Tomography Research Centre, University of Hull, Cottingham Road, Hull HU6 7RX, UK
| | - Megan A. Ayala
- Department of Chemistry and Physics, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 73096, United States
| | - Alexandria L. Foster
- Department of Chemistry and Physics, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 73096, United States
| | - Timothy J. Hubin
- Department of Chemistry and Physics, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, OK 73096, United States
| | - Kayla N. Green
- Department of Chemistry and Biochemistry, Texas Christian University, 2950 S. Bowie, Fort Worth, TX 76129, United States
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16
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Schaub S, Miska A, Becker J, Zahn S, Mollenhauer D, Sakshath S, Schünemann V, Schindler S. Synthesis of an Iron(IV) Aqua-Oxido Complex Using Ozone as an Oxidant. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201800475] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Stefan Schaub
- Institut für Anorganische und Analytische Chemie; Justus-Liebig-Universität Gießen; Heinrich-Buff-Ring 17 35392 Gießen Germany
| | - Andreas Miska
- Institut für Anorganische und Analytische Chemie; Justus-Liebig-Universität Gießen; Heinrich-Buff-Ring 17 35392 Gießen Germany
| | - Jonathan Becker
- Institut für Anorganische und Analytische Chemie; Justus-Liebig-Universität Gießen; Heinrich-Buff-Ring 17 35392 Gießen Germany
| | - Stefan Zahn
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie; Universität Leipzig; Linnéstraße 2 04103 Leipzig Germany
| | - Doreen Mollenhauer
- Institut für Physikalische Chemie; Justus-Liebig-Universität Gießen; Heinrich-Buff-Ring 17 35392 Gießen Germany
| | - Sadashivaiah Sakshath
- Fachbereich Physik; Technische Universität Kaiserslautern; Schrödinger Straße 46 67663 Kaiserslautern Germany
| | - Volker Schünemann
- Fachbereich Physik; Technische Universität Kaiserslautern; Schrödinger Straße 46 67663 Kaiserslautern Germany
| | - Siegfried Schindler
- Institut für Anorganische und Analytische Chemie; Justus-Liebig-Universität Gießen; Heinrich-Buff-Ring 17 35392 Gießen Germany
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17
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Schaub S, Miska A, Becker J, Zahn S, Mollenhauer D, Sakshath S, Schünemann V, Schindler S. Synthesis of an Iron(IV) Aqua-Oxido Complex Using Ozone as an Oxidant. Angew Chem Int Ed Engl 2018. [PMID: 29520940 DOI: 10.1002/anie.201800475] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The iron(IV) oxido complex [(tmc)Fe=O(OTf)]OTf with the macrocyclic ligand 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclo-tetradecane (tmc) has been synthesized using ozone as an oxidant. By adding water to this compound the complex [(H2 O)(tmc)Fe=O)](OTf)2 could be prepared. This complex is important in regard to a better understanding of the reactivity of FeIV oxido complexes. Mössbauer measurements using the solid compound showed an isomer shift of δ=0.19 mm s-1 and a quadrupole splitting ΔEQ =1.38 mm s-1 , confirming the high-valent FeIV state. DFT calculations were performed and led to an assignment of triplet spin multiplicity. Crystallographic characterization of [(H2 O)(tmc)Fe=O)](OTf)2 as well as of starting materials [(tmc)Fe(CH3 CN)](OTf)2 and [(tmc)Fe(OTf)]OTf together with previous results strongly suggest that [(H2 O)(tmc)Fe=O)](OTf)2 was formed similar to the oxido-hydroxido tautomerism analogous to heme systems.
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Affiliation(s)
- Stefan Schaub
- Institut für Anorganische und Analytische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392, Gießen, Germany
| | - Andreas Miska
- Institut für Anorganische und Analytische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392, Gießen, Germany
| | - Jonathan Becker
- Institut für Anorganische und Analytische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392, Gießen, Germany
| | - Stefan Zahn
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Linnéstraße 2, 04103, Leipzig, Germany
| | - Doreen Mollenhauer
- Institut für Physikalische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392, Gießen, Germany
| | - Sadashivaiah Sakshath
- Fachbereich Physik, Technische Universität Kaiserslautern, Schrödinger Straße 46, 67663, Kaiserslautern, Germany
| | - Volker Schünemann
- Fachbereich Physik, Technische Universität Kaiserslautern, Schrödinger Straße 46, 67663, Kaiserslautern, Germany
| | - Siegfried Schindler
- Institut für Anorganische und Analytische Chemie, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 17, 35392, Gießen, Germany
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18
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Mandal D, Mallick D, Shaik S. Kinetic Isotope Effect Determination Probes the Spin of the Transition State, Its Stereochemistry, and Its Ligand Sphere in Hydrogen Abstraction Reactions of Oxoiron(IV) Complexes. Acc Chem Res 2018; 51:107-117. [PMID: 29297671 DOI: 10.1021/acs.accounts.7b00442] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
This Account outlines interplay of theory and experiment in the quest to identify the reactive-spin-state in chemical reactions that possess a few spin-dependent routes. Metalloenzymes and synthetic models have forged in recent decades an area of increasing appeal, in which oxometal species bring about functionalization of hydrocarbons under mild conditions and via intriguing mechanisms that provide a glimpse of Nature's designs to harness these reactions. Prominent among these are oxoiron(IV) complexes, which are potent H-abstractors. One of the key properties of oxoirons is the presence of close-lying spin-states, which can mediate H-abstractions. As such, these complexes form a fascinating chapter of spin-state chemistry, in which chemical reactivity involves spin-state interchange, so-called two-state reactivity (TSR) and multistate reactivity (MSR). TSR and MSR pose mechanistic challenges. How can one determine the structure of the reactive transition state (TS) and its spin state for these mechanisms? Calculations can do it for us, but the challenge is to find experimental probes. There are, however, no clear kinetic signatures for the reactive-spin-state in such reactions. This is the paucity that our group has been trying to fill for sometime. Hence, it is timely to demonstrate how theory joins experiment in realizing this quest. This Account uses a set of the H-abstraction reactions of 24 synthetic oxoiron(IV) complexes and 11 hydrocarbons, together undergoing H-abstraction reactions with TSR/MSR options, which provide experimentally determined kinetic isotope effect (KIEexp) data. For this set, we demonstrate that comparing KIEexp results with calculated tunneling-augmented KIE (KIETC) data leads to a clear identification of the reactive spin-state during H-abstraction reactions. In addition, generating KIEexp data for a reaction of interest, and comparing these to KIETC values, provides the mechanistic chemist with a powerful capability to identify the reactive-TS in terms of not only its spin state but also its geometry and ligand-sphere constitution. Since tunneling "cuts through" barriers, it serves as a chemical selectivity factor. Thus, we show that in a family of oxoirons reacting with one hydrocarbon, the tunneling efficiency increases as the ligands become better electron donors. This generates counterintuitive-reactivity patterns, like antielectrophilic reactivity, and induces spin-state reactivity reversals because of differing steric demands of the corresponding 2S+1TS species, etc. Finally, for the same series, the Account reaches intuitive understanding of tunneling trends. It is shown that the increase of ligand's donicity results in electrostatic narrowing of the barrier, while the decrease of donicity and increase of bond-order asymmetry in the TS (inter alia due to Bell-Evans-Polanyi effects) broadens the barrier. Predictions are made that usage of powerful electron-donating ligands may train H-abstractors to activate the strongest C-H bond in a molecule. The concepts developed here are likely to be applicable to other oxometals in the d- and f-blocks.
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Affiliation(s)
- Debasish Mandal
- Institute of Chemistry, The Hebrew University of Jerusalem, Givat Ram Campus, 91904 Jerusalem, Israel
| | - Dibyendu Mallick
- Institute of Chemistry, The Hebrew University of Jerusalem, Givat Ram Campus, 91904 Jerusalem, Israel
| | - Sason Shaik
- Institute of Chemistry, The Hebrew University of Jerusalem, Givat Ram Campus, 91904 Jerusalem, Israel
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19
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Klein JEMN, Mandal D, Ching WM, Mallick D, Que L, Shaik S. Privileged Role of Thiolate as the Axial Ligand in Hydrogen Atom Transfer Reactions by Oxoiron(IV) Complexes in Shaping the Potential Energy Surface and Inducing Significant H-Atom Tunneling. J Am Chem Soc 2017; 139:18705-18713. [PMID: 29179544 DOI: 10.1021/jacs.7b11300] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
An H/D kinetic isotope effect (KIE) of 80 is found at -20 °C for the oxidation of 9,10-dihydroanthracene by [FeIV(O)(TMCS)]+, a complex supported by the tetramethylcyclam (TMC) macrocycle with a tethered thiolate. This KIE value approaches that previously predicted by DFT calculations. Other [FeIV(O)(TMC)(anion)] complexes exhibit values of 20, suggesting that the thiolate ligand of [FeIV(O)(TMCS)]+ plays a unique role in facilitating tunneling. Calculations show that tunneling is most enhanced (a) when the bond asymmetry between C-H bond breaking and O-H bond formation in the transition state is minimized, and (b) when the electrostatic interactions in the O---H---C moiety are maximal. These two factors-which peak for the best electron donor, the thiolate ligand-afford a slim and narrow barrier through which the H-atom can tunnel most effectively.
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Affiliation(s)
- Johannes E M N Klein
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Debasish Mandal
- Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel
| | - Wei-Min Ching
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Dibyendu Mallick
- Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Sason Shaik
- Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel
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20
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Mallick D, Shaik S. Kinetic Isotope Effect Probes the Reactive Spin State, As Well As the Geometric Feature and Constitution of the Transition State during H-Abstraction by Heme Compound II Complexes. J Am Chem Soc 2017; 139:11451-11459. [PMID: 28737390 DOI: 10.1021/jacs.7b04247] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
What do experimentally measured kinetic isotope effects (KIEs) tell us about H-abstraction reactions with multispin-state reactivity options? Using DFT calculations with tunneling corrections for experimentally studied H-abstraction reactions of porphyrin-Compound II species (Chem.-Eur. J. 2014, 20, 14437; Angew. Chem., Int. Ed. 2008, 47, 7321) with cyclohexane, dihydroanthracene (DHA), and xanthene (Xan), we show here that KIE is a selective probe that identifies the experimentally reactive spin state. At the same time, comparison of calculated and experimental KIE values permits us to determine the structural orientation of the transition states, as well as the presence/absence of an axial ligand, and the effect of porphyrin substituents. The studied compound II (Cpd II) species involve porphine, and porphyrin ligands with different meso-substituents, TPFPP (tetrakis(pentafluorophenyl)porphyrin dianion) and TMP (tetramesitylporphyrin dianion), with and without imidazole axial ligands. The DFT calculations reveal three potential pathways: quintet and triplet σ-pathways (5Hσ and 3Hσ) that possess linear transition state (TS) structures, and a triplet π -pathway (3Hπ) having a bent TS structure. Without an axial ligand, the 5Hσ pathways for these Cpd II complexes cross below the triplet states. The axial ligand raises the barriers for the quintet and triplet σ-pathways and quenches any chances for two-state reactivity, thus proceeding via the 3Hπ pathway. All of these pathways exhibit characteristic KIE values: very large for 3Hπ (48-200), small for 5Hσ (3-9), and intermediate for 3Hσ (23-51). The calculated KIEs for (TPFPP)FeIV═O without an axial ligand reveal that 3Hσ is the only pathway having a KIE that matches the experimental values, for the reactions with DHA and Xan (Angew. Chem., Int. Ed. 2008, 47, 7321). Indeed, theory shows that tunneling significantly lowers the 3Hσ barrier rendering it the sole reactive state for the reaction. A prediction is made for the reactivity and KIE of (TMP)FeIV═O complex, and a comparison is made with the analogous nonheme complexes.
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Affiliation(s)
- Dibyendu Mallick
- Institute of Chemistry and the Lise Meitner Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Sason Shaik
- Institute of Chemistry and the Lise Meitner Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
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21
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Draksharapu A, Rasheed W, Klein JEMN, Que L. Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III). Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201704322] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Apparao Draksharapu
- Department of Chemistry and Center for Metals in Biocatalysis University of Minnesota Minneapolis MN 55455 USA
| | - Waqas Rasheed
- Department of Chemistry and Center for Metals in Biocatalysis University of Minnesota Minneapolis MN 55455 USA
| | - Johannes E. M. N. Klein
- Department of Chemistry and Center for Metals in Biocatalysis University of Minnesota Minneapolis MN 55455 USA
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis University of Minnesota Minneapolis MN 55455 USA
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22
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Draksharapu A, Rasheed W, Klein JEMN, Que L. Facile and Reversible Formation of Iron(III)-Oxo-Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III). Angew Chem Int Ed Engl 2017; 56:9091-9095. [PMID: 28598024 DOI: 10.1002/anie.201704322] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Indexed: 11/09/2022]
Abstract
Ceric ammonium nitrate (CAN) or CeIV (NH4 )2 (NO3 )6 is often used in artificial water oxidation and generally considered to be an outer-sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)FeIII -O-CeIV (OH2 )(NO3 )4 ]+ (3), a complex obtained from the reaction of [(N4Py)FeII (NCMe)]2+ with 2 equiv CAN or [(N4Py)FeIV =O]2+ (2) with CeIII (NO3 )3 in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the FeIV and CeIV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S=1 FeIV in 2 to S=5/2 in 3, which is found to be facile despite the formal spin-forbidden nature of this process. This observation suggests that FeIV =O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.
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Affiliation(s)
- Apparao Draksharapu
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Waqas Rasheed
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Johannes E M N Klein
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN, 55455, USA
| | - Lawrence Que
- Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN, 55455, USA
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