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Hooper RX, Wertz AE, Shafaat HS, Holland PL. Evaluating Diazene to N 2 Interconversion at Iron-Sulfur Complexes. Chemistry 2024; 30:e202304072. [PMID: 38376370 PMCID: PMC11045311 DOI: 10.1002/chem.202304072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 02/19/2024] [Accepted: 02/20/2024] [Indexed: 02/21/2024]
Abstract
Biological N2 reduction occurs at sulfur-rich multiiron sites, and an interesting potential pathway is concerted double reduction/ protonation of bridging N2 through PCET. Here, we test the feasibility of using synthetic sulfur-supported diiron complexes to mimic this pathway. Oxidative proton transfer from μ-η1 : η1-diazene (HN=NH) is the microscopic reverse of the proposed N2 fixation pathway, revealing the energetics of the process. Previously, Sellmann assigned the purple metastable product from two-electron oxidation of [{Fe2+(PPr3)L1}2(μ-η1 : η1-N2H2)] (L1=tetradentate SSSS ligand) at -78 °C as [{Fe2+(PPr3)L1}2(μ-η1 : η1-N2)]2+, which would come from double PCET from diazene to sulfur atoms of the supporting ligands. Using resonance Raman, Mössbauer, NMR, and EPR spectroscopies in conjunction with DFT calculations, we show that the product is not an N2 complex. Instead, the data are most consistent with the spectroscopically observed species being the mononuclear iron(III) diazene complex [{Fe(PPr3)L1}(η2-N2H2)]+. Calculations indicate that the proposed double PCET has a barrier that is too high for proton transfer at the reaction temperature. Also, PCET from the bridging diazene is highly exergonic as a result of the high Fe3+/2+ redox potential, indicating that the reverse N2 protonation would be too endergonic to proceed. This system establishes the "ground rules" for designing reversible N2/N2H2 interconversion through PCET, such as tuning the redox potentials of the metal sites.
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Affiliation(s)
- Reagan X Hooper
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT-06511
| | - Ashlee E Wertz
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Ave, Columbus, OH-43210
| | - Hannah S Shafaat
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Ave, Columbus, OH-43210
- Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, CA-90095
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT-06511
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2
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Nagelski AL, Ozerov M, Fataftah MS, Krzystek J, Greer SM, Holland PL, Telser J. Electronic Structure of Three-Coordinate Fe II and Co II β-Diketiminate Complexes. Inorg Chem 2024; 63:4511-4526. [PMID: 38408452 DOI: 10.1021/acs.inorgchem.3c03388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
The β-diketiminate supporting group, [ArNCRCHCRNAr]-, stabilizes low coordination number complexes. Four such complexes, where R = tert-butyl, Ar = 2,6-diisopropylphenyl, are studied: (nacnactBu)ML, where M = FeII, CoII and L = Cl, CH3. These are denoted FeCl, FeCH3, CoCl, and CoCH3 and have been previously reported and structurally characterized. The two FeII complexes (S = 2) have also been previously characterized by Mössbauer spectroscopy, but only indirect assessment of the ligand-field splitting and zero-field splitting (zfs) parameters was available. Here, EPR spectroscopy is used, both conventional field-domain for the CoII complexes (with S = 3/2) and frequency-domain, far-infrared magnetic resonance spectroscopy (FIRMS) for all four complexes. The CoII complexes were also studied by magnetometry. These studies allow accurate determination of the zfs parameters. The two FeII complexes are similar with nearly axial zfs and large magnitude zfs given by D = -37 ± 1 cm-1 for both. The two CoII complexes likewise exhibit large and nearly axial zfs, but surprisingly, CoCl has positive D = +55 cm-1 while CoCH3 has negative D = -49 cm-1. Theoretical methods were used to probe the electronic structures of the four complexes, which explain the experimental spectra and the zfs parameters.
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Affiliation(s)
- Alexandra L Nagelski
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Mykhaylo Ozerov
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Majed S Fataftah
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - J Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States
| | - Samuel M Greer
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Joshua Telser
- Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605, United States
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3
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Bhutto SM, Hooper RX, McWilliams SF, Mercado BQ, Holland PL. Iron(iv) alkyl complexes: electronic structure contributions to Fe-C bond homolysis and migration reactions that form N-C bonds from N 2. Chem Sci 2024; 15:3485-3494. [PMID: 38455018 PMCID: PMC10915813 DOI: 10.1039/d3sc05939a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Accepted: 01/16/2024] [Indexed: 03/09/2024] Open
Abstract
High-valent iron alkyl complexes are rare, as they are prone to Fe-C bond homolysis. Here, we describe an unusual way to access formally iron(iv) alkyl complexes through double silylation of iron(i) alkyl dinitrogen complexes to form an NNSi2 group. Spectroscopically validated computations show that the disilylehydrazido(2-) ligand stabilizes the formal iron(iv) oxidation state through a strongly covalent Fe-N π-interaction, in which one π-bond fits an "inverted field" description. This means that the two bonding electrons are localized more on the metal than the ligand, and thus an iron(ii) resonance structure is a significant contributor, similar to the previously-reported phenyl analogue. However, in contrast to the phenyl complex which has an S = 1 ground state, the ground state of the alkyl complex is S = 2, which places one electron in the π* orbital, leading to longer and weaker Fe-N bonds. The reactivity of these hydrazido(2-) complexes is dependent on the steric and electronic properties of the specific alkyl group. When the alkyl group is the bulky trimethylsilylmethyl, the formally iron(iv) species is stable at room temperature and no migration of the alkyl ligand is observed. However, the analogous complex with the smaller methyl ligand does indeed undergo migration of the carbon-based ligand to the NNSi2 group to form a new N-C bond. This migration is followed by isomerization of the hydrazido ligand, and the product exists as two isomers that have distinct η1 and η2 binding of the hydrazido group. Lastly, when the alkyl group is benzyl, the Fe-C bond homolyzes to give a three-coordinate hydrazido(2-) complex which is likely due to the greater stability of a benzyl radical compared to that for methyl or trimethylsilylmethyl. These studies demonstrate the availability of a hydrocarbyl migration pathway at formally iron(iv) centers to form new N-C bonds directly to N2, though product selectivity is highly dependent on the identity of the migrating group.
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Affiliation(s)
- Samuel M Bhutto
- Department of Chemistry, Yale University New Haven Connecticut 06520 USA
| | - Reagan X Hooper
- Department of Chemistry, Yale University New Haven Connecticut 06520 USA
| | - Sean F McWilliams
- Department of Chemistry, Yale University New Haven Connecticut 06520 USA
| | - Brandon Q Mercado
- Department of Chemistry, Yale University New Haven Connecticut 06520 USA
| | - Patrick L Holland
- Department of Chemistry, Yale University New Haven Connecticut 06520 USA
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4
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Wilson DWN, Fataftah MS, Mathe Z, Mercado BQ, DeBeer S, Holland PL. Three-Coordinate Nickel and Metal-Metal Interactions in a Heterometallic Iron-Sulfur Cluster. J Am Chem Soc 2024; 146:4013-4025. [PMID: 38308743 PMCID: PMC10993082 DOI: 10.1021/jacs.3c12157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2024]
Abstract
Biological multielectron reactions often are performed by metalloenzymes with heterometallic sites, such as anaerobic carbon monoxide dehydrogenase (CODH), which has a nickel-iron-sulfide cubane with a possible three-coordinate nickel site. Here, we isolate the first synthetic iron-sulfur clusters having a nickel atom with only three donors, showing that this structural feature is feasible. These have a core with two tetrahedral irons, one octahedral tungsten, and a three-coordinate nickel connected by sulfide and thiolate bridges. Electron paramagnetic resonance (EPR), Mössbauer, and superconducting quantum interference device (SQUID) data are combined with density functional theory (DFT) computations to show how the electronic structure of the cluster arises from strong magnetic coupling between the Ni, Fe, and W sites. X-ray absorption spectroscopy, together with spectroscopically validated DFT analysis, suggests that the electronic structure can be described with a formal Ni1+ atom participating in a nonpolar Ni-W σ-bond. This metal-metal bond, which minimizes spin density at Ni1+, is conserved in two cluster oxidation states. Fe-W bonding is found in all clusters, in one case stabilizing a local non-Hund state at tungsten. Based on these results, we compare different M-M interactions and speculate that other heterometallic clusters, including metalloenzyme active sites, could likewise store redox equivalents and stabilize low-valent metal centers through metal-metal bonding.
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Affiliation(s)
- Daniel W. N. Wilson
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA
| | - Majed S. Fataftah
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA
| | - Zachary Mathe
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Patrick L. Holland
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, USA
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5
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Wilson CV, Holland PL. Mechanism of Alkene Hydrofunctionalization by Oxidative Cobalt(salen) Catalyzed Hydrogen Atom Transfer. J Am Chem Soc 2024; 146:2685-2700. [PMID: 38227206 PMCID: PMC10872242 DOI: 10.1021/jacs.3c12329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2024]
Abstract
Oxidative MHAT hydrofunctionalization of alkenes provides a mild cobalt-catalyzed route to forming C-N and C-O bonds. Here, we characterize relevant salen-supported cobalt complexes and their reactions with alkenes, silanes, oxidant, and solvent. These stoichiometric investigations are complemented by kinetic studies of the catalytic reaction and catalyst speciation. We describe the solution characterization of an elusive cobalt(III) fluoride complex, which surprisingly is not the species that reacts with silane under catalytic conditions; rather, a cobalt(III) aquo complex is more active. Accordingly, the addition of water (0.15 M) speeds the catalytic reaction, and kinetic studies show that water addition enables catalytic product formation in 2 h at -50 °C in acetone. Under these conditions, cobalt(III) resting states can be observed by UV-vis spectrophotometry, including a cobalt(III)-alkyl complex. It comes from a transient cobalt(III) hydride complex that is formed in the turnover-limiting step of the catalytic cycle. This hydride readily degrades but not to H2; it releases H+ through a bimetallic pathway that explains the [Co]2 dependence of the off-cycle reaction. In contrast, the rate of the catalytic reaction follows the power law kobs[Co]1[silane]1. Because of the different [Co] dependence of the catalytic reaction and the degradation reaction, lower catalyst loading improves the yield of the catalytic reaction by reducing the relative rate of unproductive silane/oxidant consumption. These studies illuminate mechanistic details of oxidative MHAT hydrofunctionalization of alkenes and lay the groundwork for understanding other catalytic reactions mediated by cobalt hydride and cobalt alkyl complexes.
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Affiliation(s)
- Conner V. Wilson
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT 06520, USA
| | - Patrick L. Holland
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT 06520, USA
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6
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Fataftah MS, Mercado BQ, Holland PL. Valence Delocalization and Metal-Metal Bonding in Carbon-Bridged Mixed-Valence Iron Complexes. Chemistry 2023; 29:e202301962. [PMID: 37574453 PMCID: PMC10843690 DOI: 10.1002/chem.202301962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 08/08/2023] [Accepted: 08/08/2023] [Indexed: 08/15/2023]
Abstract
The carbide ligand in the iron-molybdenum cofactor (FeMoco) in nitrogenase bridges iron atoms in different oxidation states, yet it is difficult to discern its ability to mediate magnetic exchange interactions due to the structural complexity of the cofactor. Here, we describe two mixed-valent diiron complexes with C-based ketenylidene bridging ligands, and compare the carbon bridges with the more familiar sulfur bridges. The ground state of the [Fe2 (μ-CCO)2 ]+ complex with two carbon bridges (4) is S=1 / 2 ${{ 1/2 }}$ , and it is valence delocalized on the Mössbauer timescale with a small thermal barrier for electron hopping that stems from the low Fe-C force constant. In contrast, one-electron reduction of the [Fe2 (μ-CCO)] complex with one carbon bridge (2) affords a mixed-valence species with a high-spin ground state (S=7 / 2 ${ 7/2 }$ ), and the Fe-Fe distance contracts by 1 Å. Spectroscopic, magnetic, and computational studies of the latter reveal an Fe-Fe bonding interaction that leads to complete valence delocalization. Analysis of near-IR intervalence charge transfer transitions in 5 indicates a very large double exchange constant (B) in the range of 780-965 cm-1 . These results show that carbon bridges are extremely effective at stabilizing valence delocalized ground states in mixed-valent iron dimers.
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Affiliation(s)
- Majed S Fataftah
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT-06511, USA
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT-06511, USA
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, CT-06511, USA
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7
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Wandzilak A, Grubel K, Skubi KL, McWilliams SF, Bessas D, Rana A, Hugenbruch S, Dey A, Holland PL, DeBeer S. Mössbauer and Nuclear Resonance Vibrational Spectroscopy Studies of Iron Species Involved in N-N Bond Cleavage. Inorg Chem 2023; 62:18449-18464. [PMID: 37902987 PMCID: PMC10647920 DOI: 10.1021/acs.inorgchem.3c02594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Indexed: 11/01/2023]
Abstract
Diketiminate-supported iron complexes are capable of cleaving the strong triple bond of N2 to give a tetra-iron complex with two nitrides (Rodriguez et al., Science, 2011, 334, 780-783). The mechanism of this reaction has been difficult to determine, but a transient green species was observed during the reaction that corresponds to a potential intermediate. Here, we describe studies aiming to identify the characteristics of this intermediate, using a range of spectroscopic techniques, including Mössbauer spectroscopy, electronic absorption spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and nuclear resonance vibrational spectroscopy (NRVS) complemented by density functional theory (DFT) calculations. We successfully elucidated the nature of the starting iron(II) species and the bis(nitride) species in THF solution, and in each case, THF breaks up the multiiron species. Various observations on the green intermediate species indicate that it has one N2 per two Fe atoms, has THF associated with it, and has NRVS features indicative of bridging N2. Computational models with a formally diiron(0)-N2 core are most consistent with the accumulated data, and on this basis, a mechanism for N2 splitting is suggested. This work shows the power of combining NRVS, Mössbauer, NMR, and vibrational spectroscopies with computations for revealing the nature of transient iron species during N2 cleavage.
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Affiliation(s)
- Aleksandra Wandzilak
- Max
Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr 45470, Germany
- Faculty
of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow 30-059, Poland
| | - Katarzyna Grubel
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Kazimer L. Skubi
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
- Department
of Chemistry, Carleton College, Northfield, Minnesota 55057, United States
| | - Sean F. McWilliams
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Dimitrios Bessas
- European
Synchrotron Radiation Facility, Grenoble F-38043, France
| | - Atanu Rana
- Max
Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr 45470, Germany
- School of
Chemical Science, Indian Association for
the Cultivation of Science, Kolkata 700032, India
| | - Stefan Hugenbruch
- Max
Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr 45470, Germany
| | - Abhishek Dey
- School of
Chemical Science, Indian Association for
the Cultivation of Science, Kolkata 700032, India
| | - Patrick L. Holland
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Serena DeBeer
- Max
Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr 45470, Germany
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8
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Genoux A, Pauly M, Rooney CL, Choi C, Shang B, McGuigan S, Fataftah MS, Kayser Y, Suhr SCB, DeBeer S, Wang H, Maggard PA, Holland PL. Well-Defined Iron Sites in Crystalline Carbon Nitride. J Am Chem Soc 2023; 145:20739-20744. [PMID: 37703184 DOI: 10.1021/jacs.3c05417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/15/2023]
Abstract
Carbon nitride materials can be hosts for transition metal sites, but Mössbauer studies on iron complexes in carbon nitrides have always shown a mixture of environments and oxidation states. Here we describe the synthesis and characterization of a crystalline carbon nitride with stoichiometric iron sites that all have the same environment. The material (formula C6N9H2Fe0.4Li1.2Cl, abbreviated PTI/FeCl2) is derived from reacting poly(triazine imide)·LiCl (PTI/LiCl) with a low-melting FeCl2/KCl flux, followed by anaerobic rinsing with methanol. X-ray diffraction, X-ray absorption and Mössbauer spectroscopies, and SQUID magnetometry indicate that there are tetrahedral high-spin iron(II) sites throughout the material, all having the same geometry. The material is active for electrocatalytic nitrate reduction to ammonia, with a production rate of ca. 0.1 mmol cm-2 h-1 and Faradaic efficiency of ca. 80% at -0.80 V vs RHE.
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Affiliation(s)
- Alexandre Genoux
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Magnus Pauly
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States
| | - Conor L Rooney
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Chungseok Choi
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Bo Shang
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Scott McGuigan
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States
| | - Majed S Fataftah
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Yves Kayser
- Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany
| | - Simon C B Suhr
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany
| | - Hailiang Wang
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Paul A Maggard
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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9
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Hooper RX, Mercado BQ, Holland PL. Desulfurization and N 2 Binding at an Iron Complex Derived from the C-S Activation of Benzothiophene. Organometallics 2023; 42:2019-2027. [PMID: 38282963 PMCID: PMC10810089 DOI: 10.1021/acs.organomet.3c00220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Metal insertion into the C-S bonds of thiophenes is a facile route to interesting polydentate ligand scaffolds with C and S donors. Here, we describe iron-mediated C-S activation of a diphenylphosphine-functionalized benzothiophene proligand. Metalation of the proligand with "tetrakis(trimethylphosphine)iron" gives an initial five-coordinate, diamagnetic iron(II) species with two PMe3 ligands and a dianionic PCS pincer ligand. Upon one-electron reduction, a reactive anionic iron(I) complex is formed. This species then undergoes deep-seated changes, notably cleavage of C-S and C-P bonds in the supporting ligand. Substantial coordination sphere alterations accompany the ligand C-S bond activation, including loss of a sulfur anion from the S-Fe-C metallacycle and reorganization of the two PMe3 ligands. The resulting desulfurized six-coordinate PCC iron complex also has an N2 ligand trans to the vinyl C. Reducing this complex then cleaves a C-P bond in the appended diphenylphosphine, giving a phosphido arm. These ligand transformations demonstrate novel approaches to pincers with thiolates and phosphides, which would be difficult to synthesize using typical methods through free ligand salts.
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Affiliation(s)
- Reagan X. Hooper
- Department of Chemistry, Yale University, New Haven, Connecticut 06520
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10
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Abi Ghaida F, Brinkert K, Cai Y, Catlow CRA, Chen HYT, Chen P, Dacquin JP, Daisley A, El-Kadi J, Gao W, Guo J, Hargreaves JSJ, Higham MD, Holland PL, Hosono H, Irvine GJ, Irvine JTS, Kaur M, Kobayashi Y, Laassiri S, Liedtke L, MacFarlane DR, Makepeace J, McPherson IJ, Mishra V, Ntola P, Otomo S, Peters JC, Sekine Y, Shi Z, Sievers C, Stephens IEL, Sudmeier T, Torrente Murciano L, Uner D, Wang Q, Wang Y, Westhead O, Yusuf L, Zeng X. Heterogeneous catalytic and chemical looping routes to N 2 activation: general discussion. Faraday Discuss 2023; 243:198-230. [PMID: 37358417 DOI: 10.1039/d3fd90010j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
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11
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Biswas S, Brinkert K, Catlow RA, Chen HYT, El-Kadi J, Fagiolari L, Gao W, Gupta D, Hargreaves JSJ, Hatzell MC, Holland PL, Hosono H, Irvine JTS, Isaacs M, Kobayashi Y, Liedtke L, Lozano-Roche Á, MacFarlane D, Mangini A, McPherson IJ, Mishra V, Ntola P, Otomo S, Peters JC, Risch M, Rizzato L, Safeer N K M, Shylin SI, Sievers C, Sinha V, Stephens IEL, Sudmeier T, Tian F, Vincent KA, Wang Q, Wang Y, Westhead O, Yusuf L, Zuliani G. Electrocatalytic and photocatalytic routes to N 2 activation: general discussion. Faraday Discuss 2023. [PMID: 37382558 DOI: 10.1039/d3fd90007j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/30/2023]
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12
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Catlow CRA, El-Kadi J, Guan Y, Hargreaves JSJ, Holland PL, Hosono H, Isaacs M, Kaur M, Kobayashi Y, MacFarlane DR, Mishra V, Ntola P, Safeer N K M, Shylin SI, Siahrostami S, Sievers C, Singh DL, Torrente Murciano L, Tort R, Tsang SCE, Uner D, Vincent KA, Wang Q, Yusuf L. Alternative routes to NH 3 and its application: general discussion. Faraday Discuss 2023. [PMID: 37365942 DOI: 10.1039/d3fd90009f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
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13
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Abi Ghaida F, Brinkert K, Chen P, DeBeer S, Hoffman BM, Holland PL, Laxmi S, MacFarlane D, Peters JC, Peters JW, Pickett CJ, Seefeldt LC, Shylin SI, Stephens IEL, Vincent KA, Wang Q, Westhead O. Enzymatic N 2 activation: general discussion. Faraday Discuss 2023. [PMID: 37358386 DOI: 10.1039/d3fd90011h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
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14
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Ashley A, Brinkert K, Catlow CRA, Chen P, Abi Ghaida F, Hargreaves JSJ, Holland PL, Hosono H, Isaacs M, Lozano-Roche Á, MacFarlane D, Ntola P, Peters JC, Pickett CJ, Shi Z, Singh DL, Sinha V, Uner D, Vincent KA, Wang Y, Wang Q, Zeng X. Homogeneous N 2 activation: general discussion. Faraday Discuss 2023. [PMID: 37351849 DOI: 10.1039/d3fd90008h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/24/2023]
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15
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Abstract
Alkynyl complexes of low-coordinate transition metals offer a sterically open environment and interesting bonding opportunities. Here, we explore the capacity of iron(I) alkynyl complexes to bind N2 and isolate a N2 complex including its X-ray crystal structure. Silylation of the N2 complex gives an isolable, formally iron(IV) complex with a disilylhydrazido(2-) ligand, but natural bond orbital analysis indicates that an iron(II) formulation is preferable. The structure of this compound is similar to an earlier reported phenyl complex in which phenyl migration forms a new N-C bond, but the alkynyl group does not migrate. DFT calculations are used to test the possible reasons why the alkynyl is resistant to migration, and these show that the large Fe-C bond energy in the alkynyl complex is a factor that could contribute to the lack of migration.
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Affiliation(s)
- Samuel M Bhutto
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
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16
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Abstract
Described here is a method for intermolecular hydroalkoxylation and hydrocarboxylation of 2-azadienes through cobalt-catalyzed hydrogen atom transfer and oxidation. This protocol provides a source of 2-azaallyl cation equivalents under mild conditions, is chemoselective in the presence of other C═C double bonds, and requires no excess amount of added alcohol or oxidant. Mechanistic studies suggest that the selectivity arises from lowering the transition state that leads to the highly stabilized 2-azaallyl radical.
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Affiliation(s)
- Juan M I Serviano
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Erik J T Phipps
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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17
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Bhutto SM, Hooper RX, Mercado BQ, Holland PL. Mechanism of Nitrogen-Carbon Bond Formation from Iron(IV) Disilylhydrazido Intermediates during N 2 Reduction. J Am Chem Soc 2023; 145:4626-4637. [PMID: 36794981 DOI: 10.1021/jacs.2c12382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
We recently reported a reaction sequence that activates C-H bonds in simple arenes as well as the N-N triple bond in N2, delivering the aryl group to N2 to form a new N-C bond (Nature 2020, 584, 221). This enables the transformation of abundant feedstocks (arenes and N2) into N-containing organic compounds. The key N-C bond forming step occurs upon partial silylation of N2. However, the pathway through which reduction, silylation, and migration occurred was unknown. Here, we describe synthetic, structural, magnetic, spectroscopic, kinetic, and computational studies that elucidate the steps of this transformation. N2 must be silylated twice at the distal N atom before aryl migration can occur, and sequential silyl radical and silyl cation addition is a kinetically competent pathway to a formally iron(IV)-NN(SiMe3)2 intermediate that can be isolated at low temperature. Kinetic studies show its first-order conversion to the migrated product, and DFT calculations indicate a concerted transition state for migration. The electronic structure of the formally iron(IV) intermediate is examined using DFT and CASSCF calculations, which reveal contributions from iron(II) and iron(III) resonance forms with oxidized NNSi2 ligands. The depletion of electron density from the Fe-coordinated N atom makes it electrophilic enough to accept the incoming aryl group. This new pathway for the N-C bond formation offers a method for functionalizing N2 using organometallic chemistry.
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Affiliation(s)
- Samuel M Bhutto
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
| | - Reagan X Hooper
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, Connecticut 06520, United States
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18
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McWilliams SF, Mercado BQ, MacLeod KC, Fataftah MS, Tarrago M, Wang X, Bill E, Ye S, Holland PL. Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an S = 3 ground state. Chem Sci 2023; 14:2303-2312. [PMID: 36873832 PMCID: PMC9977447 DOI: 10.1039/d2sc06412j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Accepted: 01/17/2023] [Indexed: 02/11/2023] Open
Abstract
Hydride complexes are important in catalysis and in iron-sulfur enzymes like nitrogenase, but the impact of hydride mobility on local iron spin states has been underexplored. We describe studies of a dimeric diiron(ii) hydride complex using X-ray and neutron crystallography, Mössbauer spectroscopy, magnetism, DFT, and ab initio calculations, which give insight into the dynamics and the electronic structure brought about by the hydrides. The two iron sites in the dimer have differing square-planar (intermediate-spin) and tetrahedral (high-spin) iron geometries, which are distinguished only by the hydride positions. These are strongly coupled to give an S total = 3 ground state with substantial magnetic anisotropy, and the merits of both localized and delocalized spin models are discussed. The dynamic nature of the sites is dependent on crystal packing, as shown by changes during a phase transformation that occurs near 160 K. The change in dynamics of the hydride motion leads to insight into its influence on the electronic structure. The accumulated data indicate that the two sites can trade geometries by rotating the hydrides, at a rate that is rapid above the phase transition temperature but slow below it. This small movement of the hydrides causes large changes in the ligand field because they are strong-field ligands. This suggests that hydrides could be useful in catalysis not only due to their reactivity, but also due to their ability to rapidly modulate the local electronic structure and spin states at metal sites.
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Affiliation(s)
| | | | - K Cory MacLeod
- Department of Chemistry, Yale University New Haven Connecticut USA
| | - Majed S Fataftah
- Department of Chemistry, Yale University New Haven Connecticut USA
| | - Maxime Tarrago
- Max Planck Institute for Chemical Energy Conversion Mülheim an der Ruhr Germany
| | - Xiaoping Wang
- Neutron Sciences Directorate, Oak Ridge National Laboratory Oak Ridge Tennessee USA
| | - Eckhard Bill
- Max Planck Institute for Chemical Energy Conversion Mülheim an der Ruhr Germany
| | - Shengfa Ye
- Max Planck Institute for Chemical Energy Conversion Mülheim an der Ruhr Germany
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Dalian China
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19
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Chabeda D, Kelly HR, Holland PL, Batista VS. Small, Electron-Donating Substituents Give CO 2 Activation by Permethylpentalene Zirconium Amido Complexes the Upper Hand: A DFT Study of Distortion and Interaction. Inorg Chem 2023; 62:3000-3006. [PMID: 36752721 DOI: 10.1021/acs.inorgchem.2c03533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
An insight into factors controlling CO2 activation is necessary to develop molecular systems that utilize CO2 as a chemical feedstock. Two permethylpentalene zirconium cyclopentadienyl (mono)amido complexes, Pn*ZrCp(NR2), were previously assessed for CO2 activation, and a strong dependence on the amido substituent was observed. The R = Me analogue reacted rapidly and quantitatively at room temperature to form the carbamato complex, while the R = Ph species was inert. Here, we investigate the origin of this reactivity difference using DFT and the distortion-interaction model to characterize steric and electronic contributions to the activation barrier. We find that the barrier for CO2 insertion with R = Me (19.1 kcal/mol) is lower than with R = Ph (36.6 kcal/mol), explaining the inertness of the Ph-substituted analogue. The distortion energy trend follows the steric bulk of the amido substituents, and the bulkier Ph-substituted complex has a consistently higher distortion energy along its potential energy surface than that of the Me-substituted complex. The interaction energy trend follows the electronics, and a more electron-donating Me-substituted complex shows a consistently lower interaction energy. The balance of these effects at the corresponding TS gives a reduced activation barrier. Small, electron-donating substituents therefore facilitate CO2 activation in these complexes.
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Affiliation(s)
- Daniel Chabeda
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - H Ray Kelly
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.,Yale Energy Sciences Institute, Yale University, West Haven, Connecticut 06516, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Victor S Batista
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.,Yale Energy Sciences Institute, Yale University, West Haven, Connecticut 06516, United States
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20
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Hasanayn F, Holland PL, Goldman AS, Miller AJM. Lewis Structures and the Bonding Classification of End-on Bridging Dinitrogen Transition Metal Complexes. J Am Chem Soc 2023; 145:4326-4342. [PMID: 36796367 PMCID: PMC9983020 DOI: 10.1021/jacs.2c12243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
The activation of dinitrogen by coordination to transition metal ions is a widely used and promising approach to the utilization of Earth's most abundant nitrogen source for chemical synthesis. End-on bridging N2 complexes (μ-η1:η1-N2) are key species in nitrogen fixation chemistry, but a lack of consensus on the seemingly simple task of assigning a Lewis structure for such complexes has prevented application of valence electron counting and other tools for understanding and predicting reactivity trends. The Lewis structures of bridging N2 complexes have traditionally been determined by comparing the experimentally observed NN distance to the bond lengths of free N2, diazene, and hydrazine. We introduce an alternative approach here and argue that the Lewis structure should be assigned based on the total π-bond order in the MNNM core (number of π-bonds), which derives from the character (bonding or antibonding) and occupancy of the delocalized π-symmetry molecular orbitals (π-MOs) in MNNM. To illustrate this approach, the complexes cis,cis-[(iPr4PONOP)MCl2]2(μ-N2) (M = W, Re, and Os) are examined in detail. Each complex is shown to have a different number of nitrogen-nitrogen and metal-nitrogen π-bonds, indicated as, respectively: W≡N-N≡W, Re═N═N═Re, and Os-N≡N-Os. It follows that each of these Lewis structures represents a distinct class of complexes (diazanyl, diazenyl, and dinitrogen, respectively), in which the μ-N2 ligand has a different electron donor number (total of 8e-, 6e-, or 4e-, respectively). We show how this classification can greatly aid in understanding and predicting the properties and reactivity patterns of μ-N2 complexes.
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Affiliation(s)
- Faraj Hasanayn
- Department
of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon,E-mail: (F.H.)
| | - Patrick L. Holland
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Alan S. Goldman
- Department
of Chemistry and Chemical Biology, Rutgers,
The State University of New Jersey, New Brunswick, New Jersey 08903, United States
| | - Alexander J. M. Miller
- Department
of Chemistry, University of North Carolina
at Chapel Hill, Chapel
Hill, North Carolina 27599-3290, United States,E-mail: (A.J.M.M.)
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21
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Wilson CV, Kim D, Sharma A, Hooper RX, Poli R, Hoffman BM, Holland PL. Cobalt-Carbon Bonding in a Salen-Supported Cobalt(IV) Alkyl Complex Postulated in Oxidative MHAT Catalysis. J Am Chem Soc 2022; 144:10361-10367. [PMID: 35657101 DOI: 10.1021/jacs.2c02128] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The catalytic hydrofunctionalization of alkenes through radical-polar crossover metal hydrogen atom transfer (MHAT) offers a mild pathway for the introduction of functional groups in sterically congested environments. For M = Co, this reaction is often proposed to proceed through secondary alkylcobalt(IV) intermediates, which have not been characterized unambiguously. Here, we characterize a metastable (salen)Co(isopropyl) cation, which is capable of forming C-O bonds with alcohols as proposed in the catalytic reaction. Electron nuclear double resonance (ENDOR) spectroscopy of this formally cobalt(IV) species establishes the presence of the cobalt-carbon bond, and accompanying DFT calculations indicate that the unpaired electron is localized on the cobalt center. Both experimental and computational studies show that the cobalt(IV)-carbon bond is stronger than the analogous bond in its cobalt(III) analogue, which is opposite of the usual oxidation state trend of bond energies. This phenomenon is attributable to an inverted ligand field that gives the bond Coδ--Cδ+ character and explains its electrophilic reactivity at the alkyl group. The inverted Co-C bond polarity also stabilizes the formally cobalt(IV) alkyl complex so that it is accessible at unusually low potentials. Even another cobalt(III) complex, [(salen)CoIII]+, is capable of oxidizing (salen)CoIII(iPr) to the formally cobalt(IV) state. These results give insight into the electronic structure, energetics, and reactivity of a key reactive intermediate in oxidative MHAT catalysis.
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Affiliation(s)
- Conner V Wilson
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Dongyoung Kim
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Ajay Sharma
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Reagan X Hooper
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Rinaldo Poli
- CNRS, Laboratoire de Chimie de Coordination, Université de Toulouse, F-31077 Toulouse Cedex, France
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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22
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Connor GP, Delony D, Weber JE, Mercado BQ, Curley JB, Schneider S, Mayer JM, Holland PL. Facile conversion of ammonia to a nitride in a rhenium system that cleaves dinitrogen. Chem Sci 2022; 13:4010-4018. [PMID: 35440977 PMCID: PMC8985503 DOI: 10.1039/d1sc04503b] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2021] [Accepted: 02/22/2022] [Indexed: 11/21/2022] Open
Abstract
Rhenium complexes with aliphatic PNP pincer ligands have been shown to be capable of reductive N2 splitting to nitride complexes. However, the conversion of the resulting nitride to ammonia has not been observed. Here, the thermodynamics and mechanism of the hypothetical N–H bond forming steps are evaluated through the reverse reaction, conversion of ammonia to the nitride complex. Depending on the conditions, treatment of a rhenium(iii) precursor with ammonia gives either a bis(amine) complex [(PNP)Re(NH2)2Cl]+, or results in dehydrohalogenation to the rhenium(iii) amido complex, (PNP)Re(NH2)Cl. The N–H hydrogen atoms in this amido complex can be abstracted by PCET reagents which implies that they are quite weak. Calorimetric measurements show that the average bond dissociation enthalpy of the two amido N–H bonds is 57 kcal mol−1, while DFT computations indicate a substantially weaker N–H bond of the putative rhenium(iv)-imide intermediate (BDE = 38 kcal mol−1). Our analysis demonstrates that addition of the first H atom to the nitride complex is a thermochemical bottleneck for NH3 generation. Rhenium–PNP complexes split N2 to nitrides, but the nitrides do not give ammonia. Here, the thermodynamics of the hypothetical N–H bond forming steps are evaluated through the reverse reaction, showing that the first H addition is the bottleneck.![]()
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Affiliation(s)
- Gannon P Connor
- Department of Chemistry, Yale University New Haven Connecticut USA
| | - Daniel Delony
- Institute of Inorganic Chemistry, Georg-August-Universität Göttingen Göttingen Germany
| | - Jeremy E Weber
- Department of Chemistry, Yale University New Haven Connecticut USA
| | | | - Julia B Curley
- Department of Chemistry, Yale University New Haven Connecticut USA
| | - Sven Schneider
- Institute of Inorganic Chemistry, Georg-August-Universität Göttingen Göttingen Germany
| | - James M Mayer
- Department of Chemistry, Yale University New Haven Connecticut USA
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23
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Kim D, Wilson DWN, Fataftah MS, Mercado BQ, Holland PL. Spin States, Bonding and Magnetism in Mixed-Valence Iron(0)-Iron(II) Complexes. Chemistry 2022; 28:e202104431. [PMID: 34919297 PMCID: PMC8860844 DOI: 10.1002/chem.202104431] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Indexed: 11/08/2022]
Abstract
"Xenophilic" complexes offer metal-metal bonds between disparate metal sites, but the nature of the metal-metal bonding is often unclear. Here, we describe two novel complexes with unsupported Fe-Fe bonds, Lx Fe-Fp (LX = β-aldiminate or β-diketiminate; Fp = Fe(CO)2 Cp), that offer insight into Fe-Fe bonding. Mössbauer, magnetism, and DFT analysis indicate that the most accurate electronic structure description is LFeII ←Fe0 (CO)2 Cp, in which the Fe(CO)2 Cp is low-spin iron(0) and acts as an X-type ligand toward the high-spin iron(II) of the LFe fragment. This largely electrostatic interaction has a bond order of only 0.5. The three-coordinate high-spin iron(II) site has large zero-field splitting, and in addition its Mössbauer parameters can be used to rank the Fp- "metalloligand" as a donor; it is nearly as strong a donor as phosphides and alkyls.
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Affiliation(s)
- Daniel Kim
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States
| | - Daniel W N Wilson
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States
| | - Majed S Fataftah
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States
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24
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Skubi KL, Hooper RX, Mercado BQ, Bollmeyer MM, MacMillan SN, Lancaster KM, Holland PL. Iron Complexes of a Proton-Responsive SCS Pincer Ligand with a Sensitive Electronic Structure. Inorg Chem 2022; 61:1644-1658. [PMID: 34986307 PMCID: PMC8792349 DOI: 10.1021/acs.inorgchem.1c03499] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Sulfur/carbon/sulfur pincer ligands have an interesting combination of strong-field and weak-field donors, a coordination environment that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a proton-responsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N-H bond dissociation free energy, derived from the Bordwell equation, is 56 ± 2 kcal/mol. Electron paramagnetic resonance (EPR) spectroscopy and superconducting quantum interference device (SQUID) magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with a large zero field splitting, and X-ray absorption spectra show a high Fe-S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and density functional theory calculations explain this phenomenon through a change between having the doubly occupied orbital as dz2 or dyz, as the former is more influenced by the nearby positive charge.
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Affiliation(s)
- Kazimer L. Skubi
- Department of Chemistry, Yale University, New Haven, Connecticut 06511
| | - Reagan X. Hooper
- Department of Chemistry, Yale University, New Haven, Connecticut 06511
| | | | - Melissa M. Bollmeyer
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Samantha N. MacMillan
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Kyle M. Lancaster
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
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25
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Hegg AS, Mercado BQ, Miller AJM, Holland PL. Catalytic Reduction of Dinitrogen to Ammonia using Porphyrin-Molybdenum Catalysts. Faraday Discuss 2022. [PMID: 37077158 DOI: 10.1039/d2fd00166g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Porphyrin complexes are well-known in O2 and CO2 reduction, but their application to N2 reduction has not yet been reported. Here, we show that oxo and nitrido complexes of molybdenum...
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Affiliation(s)
- Alexander S Hegg
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, USA.
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, USA.
| | - Alexander J M Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, USA.
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26
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Yamout LS, Ataya M, Hasanayn F, Holland PL, Miller AJM, Goldman AS. Understanding Terminal versus Bridging End-on N 2 Coordination in Transition Metal Complexes. J Am Chem Soc 2021; 143:9744-9757. [PMID: 34180663 DOI: 10.1021/jacs.1c01146] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Terminal and bridging end-on coordination of N2 to transition metal complexes offer possibilities for distinct pathways in ammonia synthesis and N2 functionalization. Here we elucidate the fundamental factors controlling the two binding modes and determining which is favored for a given metal-ligand system, using both quantitative density functional theory (DFT) and qualitative molecular orbital (MO) analyses. The Gibbs free energy for converting two terminal MN2 complexes into a bridging MNNM complex and a free N2 molecule (2ΔGeq°) is examined through systematic variations of the metal and ligands; values of ΔGeq° range between +9.1 and -24.0 kcal/mol per M-N2 bond. We propose a model that accounts for these broad variations by assigning a fixed π-bond order (BOπ) to the triatomic terminal MNN moiety that is equal to that of the free N2 molecule, and a variable BOπ to the bridging complexes based on the character (bonding or antibonding) and occupancy of the π-MOs in the tetratomic MNNM core. When the conversion from terminal to bridging coordination and free N2 is associated with an increase in the number of π-bonds (ΔBOeqπ > 0), the bridging mode is greatly favored; this condition is satisfied when each metal provides 1, 2, or 3 electrons to the π-MOs of the MNNM core. When each metal in the bridging complex provides 4 electrons to the MNNM π-MOs, ΔBOeqπ = 0; the equilibrium in this case is approximately ergoneutral and the direction can be shifted by dispersion interactions.
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Affiliation(s)
- Lynn S Yamout
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Mohamad Ataya
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Alexander J M Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Alan S Goldman
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
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27
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Weber JE, Hasanayn F, Fataftah M, Mercado BQ, Crabtree RH, Holland PL. Electronic and Spin-State Effects on Dinitrogen Splitting to Nitrides in a Rhenium Pincer System. Inorg Chem 2021; 60:6115-6124. [PMID: 33847125 DOI: 10.1021/acs.inorgchem.0c03778] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bimetallic nitrogen (N2) splitting to form metal nitrides is an attractive method for N2 fixation. Although a growing number of pincer-supported systems can bind and split N2, the precise relationship between the ligand properties and N2 binding/splitting remains elusive. Here we report the first example of an N2-bridged rhenium(III) complex, [(trans-P2tBuPyrr)ReCl2]2(μ-η1:η1-N2) (P2tBuPyrr = [2,5-(CH2PtBu2)2C4H2N]-). In this case, N2 binding occurs at a higher oxidation level than that in other reported pincer analogues. Analysis of the electronic structure through computational studies shows that the weakly π-donor pincer ligand stabilizes an open-shell electronic configuration that leads to enhanced binding of N2 in the bridged complex. Utilizing SQUID magnetometry, we demonstrate a singlet ground state for this Re-N-N-Re complex, and we offer tentative explanations for antiferromagnetic coupling of the two local S = 1 sites. Reduction and subsequent heating of the rhenium(III)-dinitrogen complex leads to chloride loss and cleavage of the N-N bond with isolation of the terminal rhenium(V) nitride complex (P2tBuPyrr)ReNCl.
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Affiliation(s)
- Jeremy E Weber
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Majed Fataftah
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Robert H Crabtree
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
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28
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DiPrimio DJ, Holland PL. Repurposing metalloproteins as mimics of natural metalloenzymes for small-molecule activation. J Inorg Biochem 2021; 219:111430. [PMID: 33873051 DOI: 10.1016/j.jinorgbio.2021.111430] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Revised: 03/11/2021] [Accepted: 03/15/2021] [Indexed: 12/12/2022]
Abstract
Artificial metalloenzymes (ArMs) consist of an unnatural metal or cofactor embedded in a protein scaffold, and are an excellent platform for applying the concepts of protein engineering to catalysis. In this Focused Review, we describe the application of ArMs as simple, tunable artificial models of the active sites of complex natural metalloenzymes for small-molecule activation. In this sense, ArMs expand the strategies of synthetic model chemistry to protein-based supporting ligands with potential for participation from the second coordination sphere. We focus specifically on ArMs that are structural, spectroscopic, and functional models of enzymes for activation of small molecules like CO, CO2, O2, N2, and NO, as well as production/consumption of H2. These ArMs give insight into the identities and roles of metalloenzyme structural features within and near the cofactor. We give examples of ArM work relevant to hydrogenases, acetyl-coenzyme A synthase, superoxide dismutase, heme oxygenases, nitric oxide reductase, methyl-coenzyme M reductase, copper-O2 enzymes, and nitrogenases.
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Affiliation(s)
- Daniel J DiPrimio
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, New Haven, CT, 06520, United States.
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29
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Kim D, Pillon G, DiPrimio DJ, Holland PL. Highly Z-Selective Double Bond Transposition in Simple Alkenes and Allylarenes through a Spin-Accelerated Allyl Mechanism. J Am Chem Soc 2021; 143:3070-3074. [DOI: 10.1021/jacs.1c00856] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Daniel Kim
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Guy Pillon
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Daniel J. DiPrimio
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Patrick L. Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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30
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Peters JW, Einsle O, Dean DR, DeBeer S, Hoffman BM, Holland PL, Seefeldt LC. Comment on "Structural evidence for a dynamic metallocofactor during N 2 reduction by Mo-nitrogenase". Science 2021; 371:eabe5481. [PMID: 33574183 PMCID: PMC7931246 DOI: 10.1126/science.abe5481] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 12/18/2020] [Indexed: 01/08/2023]
Abstract
Kang et al (Reports, 19 June 2020, p. 1381) report a structure of the nitrogenase MoFe protein that is interpreted to indicate binding of N2 or an N2-derived species to the active-site FeMo cofactor. Independent refinement of the structure and consideration of biochemical evidence do not support this claim.
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Affiliation(s)
- John W Peters
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA.
| | - Oliver Einsle
- Institute of Biochemistry, Albert-Ludwigs Universität, Freiburg, Germany.
| | - Dennis R Dean
- Biochemistry Department, Virginia Tech, Blacksburg, VA 24061, USA
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | | | - Lance C Seefeldt
- Chemistry and Biochemistry, Utah State University, Logan, UT 84322, USA
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31
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Abstract
Recent experimental evidence suggests that the FeMoco of nitrogenase undergoes structural rearrangement during N2 reduction, which may result in the generation of coordinatively unsaturated iron sites with two sulfur donors and a carbon donor. In an effort to synthesize and study small-molecule model complexes with a one-carbon/two-sulfur coordination environment, we have designed two new SCS pincer ligands containing a central NHC donor accompanied by thioether- or thiolate-functionalized aryl groups. Metalation of the thioether ligand with Fe(OTf)2 gives 6-coordinate complexes in which the SCS ligand binds meridionally. In contrast, metalation of the thiolate ligand with Fe(HMDS)2 gives a four-coordinate pseudotetrahedral amide complex in which the ligand binds facially, illustrating the potential structural flexibility of these ligands. Reaction of the amide complex with a bulky monothiol gives a four-coordinate complex with a one-carbon/three-sulfur coordination environment that resembles the resting state of nitrogenase. Reaction of the amide complex with phenylhydrazine gives a product with a rare κ1-bound phenylhydrazido group which undergoes N-N cleavage to give a phenylamido complex.
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Affiliation(s)
- Amy L Speelman
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Kazimer L Skubi
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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32
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Shevick SL, Wilson CV, Kotesova S, Kim D, Holland PL, Shenvi RA. Catalytic hydrogen atom transfer to alkenes: a roadmap for metal hydrides and radicals. Chem Sci 2020; 11:12401-12422. [PMID: 33520153 PMCID: PMC7810138 DOI: 10.1039/d0sc04112b] [Citation(s) in RCA: 116] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 09/28/2020] [Indexed: 12/12/2022] Open
Abstract
Hydrogen atom transfer from metal hydrides to alkenes appears to underlie widely used catalytic methods – the mechanistic implications are fascinating.
Hydrogen atom transfer from a metal hydride (MHAT) has emerged as a powerful, if puzzling, technique in chemical synthesis. In catalytic MHAT reactions, earth-abundant metal complexes generate stabilized and unstabilized carbon-centered radicals from alkenes of various substitution patterns with robust chemoselectivity. This perspective combines organic and inorganic perspectives to outline challenges and opportunities, and to propose working models to assist further developments. We attempt to demystify the putative intermediates, the basic elementary steps, and the energetic implications, especially for cage pair formation, collapse and separation. Distinctions between catalysts with strong-field (SF) and weak-field (WF) ligand environments may explain some differences in reactivity and selectivity, and provide an organizing principle for kinetics that transcends the typical thermodynamic analysis. This blueprint should aid practitioners who hope to enter and expand this exciting area of chemistry.
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Affiliation(s)
- Sophia L Shevick
- Department of Chemistry , Scripps Research , 10550 North Torrey Pines Road , La Jolla , CA 92037 , USA
| | - Conner V Wilson
- Department of Chemistry , Yale University , 225 Prospect St. , New Haven , CT 06511 , USA
| | - Simona Kotesova
- Department of Chemistry , Scripps Research , 10550 North Torrey Pines Road , La Jolla , CA 92037 , USA
| | - Dongyoung Kim
- Department of Chemistry , Yale University , 225 Prospect St. , New Haven , CT 06511 , USA
| | - Patrick L Holland
- Department of Chemistry , Yale University , 225 Prospect St. , New Haven , CT 06511 , USA
| | - Ryan A Shenvi
- Department of Chemistry , Scripps Research , 10550 North Torrey Pines Road , La Jolla , CA 92037 , USA
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33
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McWilliams SF, Broere DLJ, Halliday CJV, Bhutto SM, Mercado BQ, Holland PL. Author Correction: Coupling dinitrogen and hydrocarbons through aryl migration. Nature 2020; 586:E10. [PMID: 32943782 DOI: 10.1038/s41586-020-2722-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Affiliation(s)
| | - Daniël L J Broere
- Department of Chemistry, Yale University, New Haven, CT, USA.,Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands
| | | | - Samuel M Bhutto
- Department of Chemistry, Yale University, New Haven, CT, USA
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34
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Bruch QJ, Connor GP, McMillion ND, Goldman AS, Hasanayn F, Holland PL, Miller AJM. Considering Electrocatalytic Ammonia Synthesis via Bimetallic Dinitrogen Cleavage. ACS Catal 2020. [DOI: 10.1021/acscatal.0c02606] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Quinton J. Bruch
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Gannon P. Connor
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Noah D. McMillion
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Alan S. Goldman
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Alexander J. M. Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
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35
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Affiliation(s)
- Patrick L Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
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36
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Affiliation(s)
- Daniel Kim
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Chi Chen
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Daniel J. Weix
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Patrick L. Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
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37
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Nagelski AL, Fataftah MS, Bollmeyer MM, McWilliams SF, MacMillan SN, Mercado BQ, Lancaster KM, Holland PL. The influences of carbon donor ligands on biomimetic multi-iron complexes for N 2 reduction. Chem Sci 2020; 11:12710-12720. [PMID: 34094466 PMCID: PMC8163302 DOI: 10.1039/d0sc03447a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The active site clusters of nitrogenase enzymes possess the only examples of carbides in biology. These are the only biological FeS clusters that are capable of reducing N2 to NH4+, implicating the central carbon and its interaction with Fe as important in the mechanism of N2 reduction. This biological question motivates study of the influence of carbon donors on the electronic structure and reactivity of unsaturated, high-spin iron centers. Here, we present functional and structural models that test the impacts of carbon donors and sulfide donors in simpler iron compounds. We report the first example of a diiron complex that is bridged by an alkylidene and a sulfide, which serves as a high-fidelity structural and spectroscopic model of a two-iron portion of the active-site cluster (FeMoco) in the resting state of Mo-nitrogenase. The model complexes have antiferromagnetically coupled pairs of high-spin iron centers, and sulfur K-edge X-ray absorption spectroscopy shows comparable covalency of the sulfide for C and S bridged species. The sulfur-bridged compound does not interact with N2 even upon reduction, but upon removal of the sulfide it becomes capable of reducing N2 to NH4+ with the addition of protons and electrons. This provides synthetic support for sulfide extrusion in the activation of nitrogenase cofactors. High-spin diiron alkylidenes give insight into the electronic structure and functional relevance of carbon in the FeMoco active site of nitrogenase.![]()
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Affiliation(s)
| | | | - Melissa M. Bollmeyer
- Department of Chemistry and Chemical Biology
- Baker Laboratory
- Cornell University
- Ithaca
- USA
| | | | - Samantha N. MacMillan
- Department of Chemistry and Chemical Biology
- Baker Laboratory
- Cornell University
- Ithaca
- USA
| | | | - Kyle M. Lancaster
- Department of Chemistry and Chemical Biology
- Baker Laboratory
- Cornell University
- Ithaca
- USA
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38
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Chen C, Dugan TR, Brennessel WW, Weix DJ, Holland PL. Correction to “ Z-Selective Alkene Isomerization by High-Spin Cobalt(II) Complexes”. J Am Chem Soc 2019; 141:19521-19522. [DOI: 10.1021/jacs.9b12184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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39
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Bruch QJ, Connor GP, Chen CH, Holland PL, Mayer JM, Hasanayn F, Miller AJM. Dinitrogen Reduction to Ammonium at Rhenium Utilizing Light and Proton-Coupled Electron Transfer. J Am Chem Soc 2019; 141:20198-20208. [DOI: 10.1021/jacs.9b10031] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Quinton J. Bruch
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Gannon P. Connor
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Chun-Hsing Chen
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Alexander J. M. Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
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40
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MacLeod KC, DiMucci IM, Zovinka EP, McWilliams SF, Mercado BQ, Lancaster KM, Holland PL. Masked Radicals: Iron Complexes of Trityl, Benzophenone, and Phenylacetylene. Organometallics 2019; 38:4224-4232. [PMID: 34103782 DOI: 10.1021/acs.organomet.9b00534] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We report the first Fe─CPh3 complex, and show that the long Fe─C bond can be disrupted by neutral π-acceptor ligands (benzophenone and phenylacetylene) to release the triphenylmethyl radical. The products are formally iron(I) complexes, but X-ray absorption spectroscopy coupled with density functional and multireference ab initio calculations indicates that the best description of all the complexes is iron(II). In the formally iron(I) complexes, this does not imply that the π-acceptor ligand has radical character, because the iron(II) description arises from doubly-occupied frontier molecular orbitals that are shared equitably by the iron and the π-acceptor ligand, and the unpaired electrons lie on the metal. Despite the lack of substantial radical character on the ligands, alkyne and ketone fragments can couple to form a high-spin iron(III) complex with a cyclized metalladihydrofuran core.
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Affiliation(s)
- K Cory MacLeod
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511
| | - Ida M DiMucci
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca New York 14853
| | - Edward P Zovinka
- Department of Chemistry, Saint Francis University, Loretto, Pennsylvania 15940
| | - Sean F McWilliams
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511
| | - Brandon Q Mercado
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca New York 14853
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511
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41
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Speelman AL, Čorić I, Van Stappen C, DeBeer S, Mercado BQ, Holland PL. Nitrogenase-Relevant Reactivity of a Synthetic Iron-Sulfur-Carbon Site. J Am Chem Soc 2019; 141:13148-13157. [PMID: 31403298 DOI: 10.1021/jacs.9b05353] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Simple synthetic compounds with only S and C donors offer a ligation environment similar to the active site of nitrogenase (FeMoco) and thus demonstrate reasonable mechanisms and geometries for N2 binding and reduction in nature. We recently reported the first example of N2 binding at a mononuclear iron site supported by only S and C donors. In this work, we report experiments that examine the mechanism of N2 binding in this system. The reduction of an iron(II) tris(thiolate) complex with 1 equiv of KC8 leads to a thermally unstable intermediate, and a combination of Mössbauer, EPR, and X-ray absorption spectroscopies identifies it as a high-spin (S = 3/2) iron(I) species that maintains coordination of all three sulfur atoms. DFT calculations suggest that this iron(I) intermediate has a pseudotetrahedral geometry that resembles the S3C iron coordination environment of the belt iron sites in the resting state of the FeMoco. Further reduction to the iron(0) oxidation level under argon causes the dissociation of one of the thiolate donors and gives an η6-arene species which reacts with N2. Thus, in this system the loss of thiolate and binding of N2 require reduction beyond the iron(I) level to the iron(0) level. Further reduction of the iron(0)-N2 complex gives a reactive, formally iron(-I) species. Treatment of the putative iron(-I) complex with weak acids gives low yields of ammonia and hydrazine, demonstrating that these nitrogenase products can be generated from N2 at a synthetic Fe-S-C site. Catalytic N2 reduction is not observed, which is attributed to protonation of the supporting ligand and degradation of the complex via ligand dissociation. Identification of the challenges in this system gives insight into the design features needed for functional biomimetic complexes.
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Affiliation(s)
- Amy L Speelman
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Ilija Čorić
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Casey Van Stappen
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany
| | - Brandon Q Mercado
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Patrick L Holland
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
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42
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Connor GP, Mercado BQ, Lant HMC, Mayer JM, Holland PL. Chemical Oxidation of a Coordinated PNP-Pincer Ligand Forms Unexpected Re–Nitroxide Complexes with Reversal of Nitride Reactivity. Inorg Chem 2019; 58:10791-10801. [PMID: 31389243 DOI: 10.1021/acs.inorgchem.9b01075] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Gannon P. Connor
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Hannah M. C. Lant
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
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43
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DeRosha DE, Arnet NA, Mercado BQ, Holland PL. A [2Fe-1S] Complex That Affords Access to Bimetallic and Higher-Nuclearity Iron-Sulfur Clusters. Inorg Chem 2019; 58:8829-8834. [PMID: 31247861 DOI: 10.1021/acs.inorgchem.9b01212] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Small, coordinatively unsaturated iron-sulfur clusters are conceived as building blocks for the diverse set of shapes of iron-sulfur clusters in biological and synthetic chemistry. Here we describe a synthetic method for preparing [2Fe-1S] clusters containing two iron(II) ions, which are supported by a relatively unhindered β-diketiminate supporting ligand. The [2Fe-1S] cluster can be isolated in the presence of trimethylphosphine, and the compound with one PMe3 on each iron(II) ion has been crystallographically characterized. The PMe3 ligands may be removed with B(C6F5)3 to give a spectroscopically characterized species with solvent ligands. This species is a versatile synthon for [2Fe-2S], [4Fe-3S], and [10Fe-8S] clusters. Crystallographic characterization of the 10Fe cluster shows that it has all iron(II) ions, and the core has two [4Fe-4S] cubes that share a face in a novel arrangement. This cluster also has two iron sites that are coordinated to solvent donors, suggesting the potential for using this type of cluster for reactivity in the future.
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Affiliation(s)
- Daniel E DeRosha
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06511 , United States
| | - Nicholas A Arnet
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06511 , United States
| | - Brandon Q Mercado
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06511 , United States
| | - Patrick L Holland
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06511 , United States
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44
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Kim D, Rahaman SMW, Mercado BQ, Poli R, Holland PL. Roles of Iron Complexes in Catalytic Radical Alkene Cross-Coupling: A Computational and Mechanistic Study. J Am Chem Soc 2019; 141:7473-7485. [PMID: 31025567 PMCID: PMC6953484 DOI: 10.1021/jacs.9b02117] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A growing and useful class of alkene coupling reactions involve hydrogen atom transfer (HAT) from a metal-hydride species to an alkene to form a free radical, which is responsible for subsequent bond formation. Here, we use a combination of experimental and computational investigations to map out the mechanistic details of iron-catalyzed reductive alkene cross-coupling, an important representative of the HAT alkene reactions. We are able to explain several observations that were previously mysterious. First, the rate-limiting step in the catalytic cycle is the formation of the reactive Fe-H intermediate, elucidating the importance of the choice of reductant. Second, the success of the catalytic system is attributable to the exceptionally weak (17 kcal/mol) Fe-H bond, which performs irreversible HAT to alkenes in contrast to previous studies on isolable hydride complexes where this addition was reversible. Third, the organic radical intermediates can reversibly form organometallic species, which helps to protect the free radicals from side reactions. Fourth, the previously accepted quenching of the postcoupling radical through stepwise electron transfer/proton transfer is not as favorable as alternative mechanisms. We find that there are two feasible pathways. One uses concerted proton-coupled electron transfer (PCET) from an iron(II) ethanol complex, which is facilitated because the O-H bond dissociation free energy is lowered by 30 kcal/mol upon metal binding. In an alternative pathway, an O-bound enolate-iron(III) complex undergoes proton shuttling from an iron-bound alcohol. These kinetic, spectroscopic, and computational studies identify key organometallic species and PCET steps that control selectivity and reactivity in metal-catalyzed HAT alkene coupling, and create a firm basis for elucidation of mechanisms in the growing class of HAT alkene cross-coupling reactions.
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Affiliation(s)
- Dongyoung Kim
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - S. M. Wahidur Rahaman
- LCC-CNRS, Université de Toulouse, INPT, 205 Route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
| | - Rinaldo Poli
- LCC-CNRS, Université de Toulouse, INPT, 205 Route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France
| | - Patrick L. Holland
- Department of Chemistry, Yale University, New Haven, Connecticut 06511, United States
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45
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Abstract
Iron catalysts are adept at breaking the N-N bond of N2, as exemplified by the iron-catalyzed Haber-Bosch process and the iron-containing clusters at the active sites of nitrogenase enzymes. This Minireview summarizes recent work that has identified a well-characterized set of multi-iron complexes that are capable of breaking and functionalizing N2, and are amenable to detailed mechanistic studies. We discuss the redox balancing, the potential intermediates during N2 activation, the variation of alkali metal reductant, the reversibility of N2 cleavage, and the formation of N-H and N-C bonds from N2.
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Affiliation(s)
- Samuel M Bhutto
- Department of Chemistry, Yale University, 225 Prospect St, New Haven, CT 06520, USA
| | - Patrick L Holland
- Department of Chemistry, Yale University, 225 Prospect St, New Haven, CT 06520, USA
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46
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Roy L, Al-Afyouni MH, DeRosha DE, Mondal B, DiMucci IM, Lancaster KM, Shearer J, Bill E, Brennessel WW, Neese F, Ye S, Holland PL. Reduction of CO 2 by a masked two-coordinate cobalt(i) complex and characterization of a proposed oxodicobalt(ii) intermediate. Chem Sci 2019; 10:918-929. [PMID: 30774886 PMCID: PMC6346294 DOI: 10.1039/c8sc02599a] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Accepted: 10/22/2018] [Indexed: 12/31/2022] Open
Abstract
Fixation and chemical reduction of CO2 are important for utilization of this abundant resource, and understanding the detailed mechanism of C-O cleavage is needed for rational development of CO2 reduction methods. Here, we describe a detailed analysis of the mechanism of the reaction of a masked two-coordinate cobalt(i) complex, L tBuCo (where L tBu = 2,2,6,6-tetramethyl-3,5-bis[(2,6-diisopropylphenyl)imino]hept-4-yl), with CO2, which yields two products of C-O cleavage, the cobalt(i) monocarbonyl complex L tBuCo(CO) and the dicobalt(ii) carbonate complex (L tBuCo)2(μ-CO3). Kinetic studies and computations show that the κN,η6-arene isomer of L tBuCo rearranges to the κ2 N,N' binding mode prior to binding of CO2, which contrasts with the mechanism of binding of other substrates to L tBuCo. Density functional theory (DFT) studies show that the only low-energy pathways for cleavage of CO2 proceed through bimetallic mechanisms, and DFT and highly correlated domain-based local pair natural orbital coupled cluster (DLPNO-CCSD(T)) calculations reveal the cooperative effects of the two metal centers during facile C-O bond rupture. A plausible intermediate in the reaction of CO2 with L tBuCo is the oxodicobalt(ii) complex L tBuCoOCoL tBu, which has been independently synthesized through the reaction of L tBuCo with N2O. The rapid reaction of L tBuCoOCoL tBu with CO2 to form the carbonate product indicates that the oxo species is kinetically competent to be an intermediate during CO2 cleavage by L tBuCo. L tBuCoOCoL tBu is a novel example of a thoroughly characterized molecular cobalt-oxo complex where the cobalt ions are clearly in the +2 oxidation state. Its nucleophilic reactivity is a consequence of high charge localization on the μ-oxo ligand between two antiferromagnetically coupled high-spin cobalt(ii) centers, as characterized by DFT and multireference complete active space self-consistent field (CASSCF) calculations.
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Affiliation(s)
- Lisa Roy
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , Mülheim an der Ruhr , D-45470 , Germany
- CSIR Central Mechanical Engineering Research Institute , Durgapur 713209 , India
| | - Malik H Al-Afyouni
- Department of Chemistry , University of Rochester , Rochester , New York 14618 , USA
| | - Daniel E DeRosha
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , USA .
| | - Bhaskar Mondal
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , Mülheim an der Ruhr , D-45470 , Germany
| | - Ida M DiMucci
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , New York 14853 , USA
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , New York 14853 , USA
| | - Jason Shearer
- Department of Chemistry , Trinity University , San Antonio , Texas 78212 , USA
| | - Eckhard Bill
- Max Planck Institute for Chemical Energy Conversion , Stiftstraße 34-36 , Mülheim an der Ruhr , D-45470 , Germany
| | - William W Brennessel
- Department of Chemistry , University of Rochester , Rochester , New York 14618 , USA
| | - Frank Neese
- Max Planck Institute for Coal Research , Kaiser-Wilhelm-Platz 1 , Mülheim an der Ruhr , D-45470 , Germany .
| | - Shengfa Ye
- Max Planck Institute for Coal Research , Kaiser-Wilhelm-Platz 1 , Mülheim an der Ruhr , D-45470 , Germany .
| | - Patrick L Holland
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , USA .
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McWilliams SF, Bunting PC, Kathiresan V, Mercado BQ, Hoffman BM, Long JR, Holland PL. Isolation and characterization of a high-spin mixed-valent iron dinitrogen complex. Chem Commun (Camb) 2018; 54:13339-13342. [PMID: 30403226 DOI: 10.1039/c8cc07294a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a rare example of a mixed-valence iron compound with an FeNNFe core, which gives insight into the structural, spectroscopic, and magnetic influences of single-electron reductions and oxidations. In the new compound, the odd electron is localized as judged from Mössbauer spectra at 80 K and infrared spectra at room temperature, and the backbonding into the N2 unit is intermediate between diiron(i) and diiron(0) congeners. Magnetic susceptibility and relaxation studies on the series of FeNNFe compounds show significant magnetic anisotropy, but through-barrier pathways enable fairly rapid magnetic relaxation.
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Affiliation(s)
- Sean F McWilliams
- Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT 06520, USA.
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48
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Rozen E, Erlich Y, Reesbeck ME, Holland PL, Sukenik CN. Functionalized Self-Assembled Monolayers Bearing Diiminate Complexes Immobilized through Covalently Anchored Ligands. Langmuir 2018; 34:13472-13480. [PMID: 29048903 DOI: 10.1021/acs.langmuir.7b00984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The application of synthetic organic chemistry to the surface chemistry of monolayer arrays adds a novel dimension to the power of these systems for surface modification. This paper describes the elaboration of simple functionalized monolayers into dialdimine and dialdiminate ligands tethered to the monolayer surface. These ligands are then used to coordinate metal ions in an effort to form diiminate complexes with control over their environment and orientation. Ligand anchoring is best achieved through either thiol-ene photochemistry or azide-acetylene "click" chemistry. There is an influence of ligand bulk on some surface transformations, and in some cases reactions that have been reported to be effective on simple, homogeneous monolayer surfaces are not applicable to a more complex monolayer environment. The large excess of solution reagents relative to monolayer surface functionality adds another measure of difficulty to the control of interfacial reactions. In instances where the anchoring chain includes functional groups that can directly interact with metal ions, the metalation of ligand-bearing surfaces resulted in a higher metal ion content than would have been expected from binding only to the diimine ligands.
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Affiliation(s)
- Elitsour Rozen
- Department of Chemistry and Institute of Nanotechnology and Advanced Materials , Bar-Ilan University , Ramat-Gan 52900 , Israel
| | - Yaron Erlich
- Department of Chemistry and Institute of Nanotechnology and Advanced Materials , Bar-Ilan University , Ramat-Gan 52900 , Israel
| | - Megan E Reesbeck
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Patrick L Holland
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Chaim N Sukenik
- Department of Chemistry and Institute of Nanotechnology and Advanced Materials , Bar-Ilan University , Ramat-Gan 52900 , Israel
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49
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Abstract
Noncovalent interactions of organic moieties with Lewis acidic alkali cations can greatly affect structure and reactivity. Herein, we describe the effects of interactions with alkali-metal cations within a series of reduced iron complexes bearing a redox-active formazanate ligand, in terms of structures, magnetism, spectroscopy, and reaction rates. In the absence of a crown ether to sequester the alkali cation, dimeric complexes are isolated wherein the formazanate has rearranged to form a five-membered metallacycle. The dissociation of these dimers is dependent on the binding mode and size of the alkali cation. In the dimers, the formazanate ligands are radical dianions, as shown by X-ray absorption spectroscopy, Mössbauer spectroscopy, and analysis of metrical parameters. These experimental measures are complemented by density functional theory calculations that show the spin density on the bridging ligands.
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Affiliation(s)
- Daniel L J Broere
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , United States
| | - Brandon Q Mercado
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , United States
| | - Eckhard Bill
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36 , D-45470 Mülheim an der Ruhr , Germany
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Baker Laboratory , Cornell University , Ithaca , New York 14853 , United States
| | - Stephen Sproules
- WestCHEM, School of Chemistry , University of Glasgow , Glasgow G12 8QQ , United Kingdom
| | - Patrick L Holland
- Department of Chemistry , Yale University , New Haven , Connecticut 06520 , United States
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50
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Chen JG, Crooks RM, Seefeldt LC, Bren KL, Bullock RM, Darensbourg MY, Holland PL, Hoffman B, Janik MJ, Jones AK, Kanatzidis MG, King P, Lancaster KM, Lymar SV, Pfromm P, Schneider WF, Schrock RR. Beyond fossil fuel-driven nitrogen transformations. Science 2018; 360:360/6391/eaar6611. [PMID: 29798857 DOI: 10.1126/science.aar6611] [Citation(s) in RCA: 714] [Impact Index Per Article: 119.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.
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Affiliation(s)
- Jingguang G Chen
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA. .,Chemistry Division, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Richard M Crooks
- Department of Chemistry, The University of Texas at Austin, Austin, TX 78712, USA.
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84332, USA.
| | - Kara L Bren
- Department of Chemistry, University of Rochester, Rochester, NY 14627, USA
| | | | | | | | - Brian Hoffman
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
| | - Michael J Janik
- Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802, USA
| | - Anne K Jones
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85282, USA
| | | | - Paul King
- National Renewable Energy Laboratory, Golden, CO 80401, USA
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853, USA
| | - Sergei V Lymar
- Chemistry Division, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Peter Pfromm
- Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, USA
| | - William F Schneider
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
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