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Zhang X, Jiang X, Zhao Q, Li Y, Feng L, Ye S, Tung CH, Wang W. Synthesis and Characterization of Bridging-Diazene Diiron Half-Sandwich Complexes: The Role of Sulfur Hydrogen Bonding. Inorg Chem 2024; 63:14040-14049. [PMID: 39007501 DOI: 10.1021/acs.inorgchem.4c01783] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/16/2024]
Abstract
We report two bridging-diazene diiron complexes [Cp*Fe(8-quinolinethiolate)]2(μ-N2H2) (1-N2H2) and [Cp*Fe(1,2-Cy2PC6H4S)]2(μ-N2H2) (2-N2H2), synthesized by the reaction of hydrazine with the corresponding thiolate-based iron half-sandwich complex, [Cp*Fe(8-quinolinethiolate)]2 (1) and Cp*Fe(1,2-Cy2PC6H4S) (2). Crystallographic analysis reveals that the thiolate sites in 1-N2H2 and 2-N2H2 can engage in N-H···S hydrogen bonding with the diazene protons. 1-N2H2 is thermally stable in both solid and solution states, allowing for one-electron oxidation to afford a cationic diazene radical complex [1-N2H2]+ at room temperature. In contrast, 2-N2H2 tends to undergo N2H2/N2 transformation, leading to the formation of a Fe(III)-H species by the loss of N2. In addition to stabilizing HN=NH species through the hydrogen bonding, the thiolate-based ligands also seem to facilitate proton-coupled electron transfer, thereby promoting N-H cleavage.
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Affiliation(s)
- Xin Zhang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Xuebin Jiang
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qiuting Zhao
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Yongxian Li
- College of Chemistry, Beijing Normal University, Beijing 100875, China
| | - Lei Feng
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Shengfa Ye
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Chen-Ho Tung
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
| | - Wenguang Wang
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
- College of Chemistry, Beijing Normal University, Beijing 100875, China
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2
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Suga Y, Sunada Y. Reduction-induced hapticity increase in a silacycle-bridged biaryl-based ligand coordinated to an iron center. Dalton Trans 2024; 53:862-865. [PMID: 37987085 DOI: 10.1039/d3dt03788f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
An Fe(II) bromide complex supported by a bidentate phosphine ligand and an η1(C)-coordinated six-membered silacycle-bridged biphenyl-based ligand is converted upon reduction into an Fe(I) complex in which the hapticity of the silacycle-based ligand increases from η1 to η5.
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Affiliation(s)
- Yuto Suga
- Department of Applied Chemistry, School of Engineering, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan
| | - Yusuke Sunada
- Department of Applied Chemistry, School of Engineering, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan
- Institute of Industrial Science, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan
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3
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Boekell NG, Bartulovich CO, Maity S, Flowers RA. Accessing Unusual Reactivity through Chelation-Promoted Bond Weakening. Inorg Chem 2023; 62:5040-5045. [PMID: 36912617 DOI: 10.1021/acs.inorgchem.3c00298] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/14/2023]
Abstract
Highly reducing Sm(II) reductants and protic ligands were used as a platform to ascertain the relationship between low-valent metal-protic ligand affinity and degree of ligand X-H bond weakening with the goal of forming potent proton-coupled electron transfer (PCET) reductants. Among the Sm(II)-protic ligand reductant systems investigated, the samarium dibromide N-methylethanolamine (SmBr2-NMEA) reagent system displayed the best combination of metal-ligand affinity and stability against H2 evolution. The use of SmBr2-NMEA afforded the reduction of a range of substrates that are typically recalcitrant to single-electron reduction including alkynes, lactones, and arenes as stable as biphenyl. Moreover, the unique role of NMEA as a chelating ligand for Sm(II) was demonstrated by the reductive cyclization of unactivated esters bearing pendant olefins in contrast to the SmBr2-water-amine system. Finally, the SmBr2-NMEA reagent system was found to reduce substrates analogous to key intermediates in the nitrogen fixation process. These results reveal SmBr2-NMEA to be a powerful reductant for a wide range of challenging substrates and demonstrate the potential for the rational design of PCET reagents with exceptionally weak X-H bonds.
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Affiliation(s)
- Nicholas G Boekell
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Caroline O Bartulovich
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Sandeepan Maity
- Department of Chemistry, C. V. Raman Global University, Bhubaneswar, Odisha 752054, India
| | - Robert A Flowers
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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4
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Pal S. Cp* non-innocence and the implications of (η 4-Cp*H)Rh intermediates in the hydrogenation of CO 2, NAD +, amino-borane, and the Cp* framework - a computational study. Dalton Trans 2023; 52:1182-1187. [PMID: 36648493 DOI: 10.1039/d2dt03611h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
In hydrogenation mediated by half-sandwich complexes of Rh, Cp*Rh(III)-H intermediates are critical hydride-delivery agents. For bipyridine-supported complexes, a unique transformation named 'Cp* non-innocence' leads to the appearance of (Cp*H)Rh(I) intermediates, which are purported to exhibit enhanced hydride-delivery capabilities. In this work, DFT calculations performed to compare the role of these complexes in hydrogenation reveal that (Cp*H)Rh(I) intermediates do not compete with the conventional pathway (involving Cp*Rh(III)-H); instead they can lead to sequential hydrogenation of the Cp* framework, and potentially, catalyst degradation. Thus, caution is warranted when invoking the truly homogeneous nature of hydrogenation catalysis mediated by this popular class of complexes.
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Affiliation(s)
- Shrinwantu Pal
- Coordination Chemistry and Catalysis Unit, Okinawa Institute of Science and Technology, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
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5
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Tresp DS, Neugebauer H, Grimme S, Hansen A, Prokopchuk DE. Electronic Effects of Aminoindenyl Ligands Coordinated to Manganese: Structures and Properties of a Mn 0 Metalloradical and Bimetallic Mn –I/Mn I Adduct. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00463] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- David S. Tresp
- Department of Chemistry, Rutgers University−Newark, Newark, New Jersey 07102, United States
| | - Hagen Neugebauer
- Mulliken Center for Theoretical Chemistry, Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Bonn 53115, Germany
| | - Stefan Grimme
- Mulliken Center for Theoretical Chemistry, Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Bonn 53115, Germany
| | - Andreas Hansen
- Mulliken Center for Theoretical Chemistry, Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Bonn 53115, Germany
| | - Demyan E. Prokopchuk
- Department of Chemistry, Rutgers University−Newark, Newark, New Jersey 07102, United States
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6
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Jain AK, Gau MR, Carroll PJ, Goldberg KI. Comparing Square-Planar Rh I and Ir I: Metal–Ligand Proton Tautomerism, Fluxionality, and Reactivity. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anant Kumar Jain
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Michael R. Gau
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Patrick J. Carroll
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Karen I. Goldberg
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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7
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Abstract
Coordination-induced bond weakening is a phenomenon wherein ligand X-H bond homolysis occurs in concert with the energetically favorable oxidation of a coordinating metal complex. The coupling of these two processes enables thermodynamically favorable proton-coupled electron transfer reductions to form weak bonds upon formal hydrogen atom transfer to substrates. Moreover, systems utilizing coordination-induced bond weakening have been shown to facilitate the dehydrogenation of feedstock molecules including water, ammonia, and primary alcohols under mild conditions. The formation of exceptionally weak substrate X-H bonds via small molecule homolysis is a powerful strategy in synthesis and has been shown to enable nitrogen fixation under mild conditions. Coordination-induced bond weakening has also been identified as an integral process in biophotosynthesis and has promising applications in renewable chemical fuel storage systems. This review presents a discussion of the advances made in the study of coordination-induced bond weakening to date. Because of the broad range of metal and ligand species implicated in coordination-induced bond weakening, each literature report is discussed individually and ordered by the identity of the low-valent metal. We then offer mechanistic insights into the basis of coordination-induced bond weakening and conclude with a discussion of opportunities for further research into the development and applications of coordination-induced bond weakening systems.
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Affiliation(s)
- Nicholas G Boekell
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Robert A Flowers
- Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States
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8
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Moreno JJ, Espada MF, Maya C, Campos J, López-Serrano J, Macgregor SA, Carmona E. Isomerization of a cationic (η5-C5Me5)Ir(III) complex involving remote C–C and C–H bond formation. Polyhedron 2021. [DOI: 10.1016/j.poly.2021.115363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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9
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Schneck F, Finger M, Siewert I, Schneider S. Solvent dependent C−H Bond Strength in a Nickel Pincer Complex. Z Anorg Allg Chem 2021. [DOI: 10.1002/zaac.202100077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Felix Schneck
- Universität Göttingen Institut für Anorganische Chemie Tammannstraße 4 37077 Göttingen Germany
| | - Markus Finger
- Universität Göttingen Institut für Anorganische Chemie Tammannstraße 4 37077 Göttingen Germany
| | - Inke Siewert
- Universität Göttingen Institut für Anorganische Chemie Tammannstraße 4 37077 Göttingen Germany
| | - Sven Schneider
- Universität Göttingen Institut für Anorganische Chemie Tammannstraße 4 37077 Göttingen Germany
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10
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Kuo JL, Goldberg KI. Metal/Ligand Proton Tautomerism Facilitates Dinuclear H 2 Reductive Elimination. J Am Chem Soc 2020; 142:21439-21449. [PMID: 33297680 DOI: 10.1021/jacs.0c10458] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Using the doubly protic bis-pyrazole-pyridine ligand (N(NNH)2), we have synthesized an octahedral IrIII-H [HIr(κ3-N(NNH)(NN-))(CO)(tBuPy)]+ ([1-MH]+) from an IrI starting material. This hydride was generated by adding sufficient electron density to the metal center such that it became the thermodynamically preferred site of protonation. It was observed via UV-vis spectroscopy that [1-MH]+ establishes a [tBuPy] dependent equilibrium with a ligand protonated square-planar IrI [Ir(N(NNH)2)(CO)]+ ([2-LH]+). This example of metal/ligand proton tautomerism is unusual in that the position of the equilibrium can be controlled by the concentration of exogeneous ligand (i.e., tBuPy). This equilibrium was shown to be key to the reactivity of the IrIII-H; 2 equiv of [1-MH]+ release H2, converting to the IrII dimer [[Ir(N(NN-)(NNH))(CO)(tBuPy)]2]2+ ([7]2+) under mild conditions (observable at room temperature). Mechanistic evidence is presented to support that this dinuclear reductive elimination occurs by tautomerization of the metal hydride [1-MH]+ to a ligand protonated species [1-LH]+, from which ligand dissociation is facile, generating [2-LH]+. Subsequent reaction of [2-LH]+ with [1-MH]+ allows for production of H2 and the IrII dimer [7]2+. The tautomerization between the metal-hydride and the ligand protonated species provides a low energy pathway for ligand dissociation, opening the needed coordination site. The ability to control the interconversion between a metal-hydride and a ligand-protonated congener using an exogeneous ligand introduces a new strategy for catalyst design with proton responsive ligands.
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Affiliation(s)
- Jonathan L Kuo
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
| | - Karen I Goldberg
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
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11
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Alférez MG, Moreno JJ, Hidalgo N, Campos J. Reversible Hydride Migration from C 5Me 5 to Rh I Revealed by a Cooperative Bimetallic Approach. Angew Chem Int Ed Engl 2020; 59:20863-20867. [PMID: 33448577 PMCID: PMC7754342 DOI: 10.1002/anie.202008442] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 07/16/2020] [Indexed: 02/06/2023]
Abstract
The use of cyclopentadienyl ligands in organometallic chemistry and catalysis is ubiquitous, mostly due to their robust spectator role. Nonetheless, increasing examples of non-innocent behaviour are being documented. Here, we provide evidence for reversible intramolecular C-H activation at one methyl terminus of C5Me5 in [(η-C5Me5)Rh(PMe3)2] to form a new Rh-H bond, a process so far restricted to early transition metals. Experimental evidence was acquired from bimetallic rhodium/gold structures in which the gold center binds either to the rhodium atom or to the activated Cp* ring. Reversibility of the C-H activation event regenerates the RhI and AuI monometallic precursors, whose cooperative reactivity towards polar E-H bonds (E=O, N), including the N-H bonds in ammonia, can be understood in terms of bimetallic frustration.
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Affiliation(s)
- Macarena G. Alférez
- Instituto de Investigaciones Químicas (IIQ)Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA)Consejo Superior de Investigaciones Científicas (CSIC)University of SevillaAvenida Américo Vespucio 4941092SevillaSpain
| | - Juan J. Moreno
- Instituto de Investigaciones Químicas (IIQ)Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA)Consejo Superior de Investigaciones Científicas (CSIC)University of SevillaAvenida Américo Vespucio 4941092SevillaSpain
| | - Nereida Hidalgo
- Instituto de Investigaciones Químicas (IIQ)Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA)Consejo Superior de Investigaciones Científicas (CSIC)University of SevillaAvenida Américo Vespucio 4941092SevillaSpain
| | - Jesús Campos
- Instituto de Investigaciones Químicas (IIQ)Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA)Consejo Superior de Investigaciones Científicas (CSIC)University of SevillaAvenida Américo Vespucio 4941092SevillaSpain
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12
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Alférez MG, Moreno JJ, Hidalgo N, Campos J. Reversible Hydride Migration from C
5
Me
5
to Rh
I
Revealed by a Cooperative Bimetallic Approach. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202008442] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Macarena G. Alférez
- Instituto de Investigaciones Químicas (IIQ) Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA) Consejo Superior de Investigaciones Científicas (CSIC) University of Sevilla Avenida Américo Vespucio 49 41092 Sevilla Spain
| | - Juan J. Moreno
- Instituto de Investigaciones Químicas (IIQ) Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA) Consejo Superior de Investigaciones Científicas (CSIC) University of Sevilla Avenida Américo Vespucio 49 41092 Sevilla Spain
| | - Nereida Hidalgo
- Instituto de Investigaciones Químicas (IIQ) Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA) Consejo Superior de Investigaciones Científicas (CSIC) University of Sevilla Avenida Américo Vespucio 49 41092 Sevilla Spain
| | - Jesús Campos
- Instituto de Investigaciones Químicas (IIQ) Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA) Consejo Superior de Investigaciones Científicas (CSIC) University of Sevilla Avenida Américo Vespucio 49 41092 Sevilla Spain
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13
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Arnett CH, Bogacz I, Chatterjee R, Yano J, Oyala PH, Agapie T. Mixed-Valent Diiron μ-Carbyne, μ-Hydride Complexes: Implications for Nitrogenase. J Am Chem Soc 2020; 142:18795-18813. [PMID: 32976708 DOI: 10.1021/jacs.0c05920] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Binding of N2 by the FeMo-cofactor of nitrogenase is believed to occur after transfer of 4 e- and 4 H+ equivalents to the active site. Although pulse EPR studies indicate the presence of two Fe-(μ-H)-Fe moieties, the structural and electronic features of this mixed valent intermediate remain poorly understood. Toward an improved understanding of this bioorganometallic cluster, we report herein that diiron μ-carbyne complex (P6ArC)Fe2(μ-H) can be oxidized and reduced, allowing for the first time spectral characterization of two EPR-active Fe(μ-C)(μ-H)Fe model complexes linked by a 2 e- transfer which bear some resemblance to a pair of En and En+2 states of nitrogenase. Both species populate S = 1/2 states at low temperatures, and the influence of valence (de)localization on the spectroscopic signature of the μ-hydride ligand was evaluated by pulse EPR studies. Compared to analogous data for the {Fe2(μ-H)}2 state of FeMoco (E4(4H)), the data and analysis presented herein suggest that the hydride ligands in E4(4H) bridge isovalent (most probably FeIII) metal centers. Although electron transfer involves metal-localized orbitals, investigations of [(P6ArC)Fe2(μ-H)]+1 and [(P6ArC)Fe2(μ-H)]-1 by pulse EPR revealed that redox chemistry induces significant changes in Fe-C covalency (-50% upon 2 e- reduction), a conclusion further supported by X-ray absorption spectroscopy, 57Fe Mössbauer studies, and DFT calculations. Combined, our studies demonstrate that changes in covalency buffer against the accumulation of excess charge density on the metals by partially redistributing it to the bridging carbon, thereby facilitating multielectron transformations.
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Affiliation(s)
- Charles H Arnett
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Isabel Bogacz
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Ruchira Chatterjee
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Junko Yano
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Paul H Oyala
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Theodor Agapie
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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14
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Schild DJ, Drover MW, Oyala PH, Peters JC. Generating Potent C-H PCET Donors: Ligand-Induced Fe-to-Ring Proton Migration from a Cp*Fe III-H Complex Demonstrates a Promising Strategy. J Am Chem Soc 2020; 142:18963-18970. [PMID: 33103877 DOI: 10.1021/jacs.0c09363] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Highly reactive organometallic species that mediate reductive proton-coupled electron transfer (PCET) reactions are an exciting area for development in catalysis, where a key objective focuses on tuning the reactivity of such species. This work pursues ligand-induced activation of a stable organometallic complex toward PCET reactivity. This is studied via the conversion of a prototypical Cp*FeIII-H species, [FeIII(η5-Cp*)(dppe)H]+ (Cp* = C5Me5-, dppe = 1,2-bis(diphenylphosphino)ethane), to a highly reactive, S = 1/2 ring-protonated endo-Cp*H-Fe relative, triggered by the addition of CO. Our assignment of the latter ring-protonated species contrasts with its previous reported formulation, which instead assigned it as a hypervalent 19-electron hydride, [FeIII(η5-Cp*)(dppe)(CO)H]+. Herein, pulse EPR spectroscopy (1,2H HYSCORE, ENDOR) and X-ray crystallography, with corresponding DFT studies, cement its assignment as the ring-protonated isomer, [FeI(endo-η4-Cp*H)(dppe)(CO)]+. A less sterically shielded and hence more reactive exo-isomer can be generated through oxidation of a stable Fe0(exo-η4-Cp*H)(dppe)(CO) precursor. Both endo- and exo-ring-protonated isomers are calculated to have an exceptionally low bond dissociation free energy (BDFEC-H ≈ 29 kcal mol-1 and 25 kcal mol-1, respectively) cf. BDFEFe-H of 56 kcal mol-1 for [FeIII(η5-Cp*)(dppe)H]+. These weak C-H bonds are shown to undergo proton-coupled electron transfer (PCET) to azobenzene to generate diphenylhydrazine and the corresponding closed-shell [FeII(η5-Cp*)(dppe)CO]+ byproduct.
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Affiliation(s)
- Dirk J Schild
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Marcus W Drover
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Paul H Oyala
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Jonas C Peters
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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15
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Rennie BE, Eleftheriades RG, Morris RH. Systematic Trends in the Electrochemical Properties of Transition Metal Hydride Complexes Discovered by Using the Ligand Acidity Constant Equation. J Am Chem Soc 2020; 142:17607-17629. [PMID: 32941024 DOI: 10.1021/jacs.0c08000] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the thermodynamics of paramagnetic transition metal hydride complexes, especially of the abundant 3d metals, is important in the design of electrocatalysts and organometallic catalysts. The pKaMeCN([MHLn]+/[MLn) of paramagnetic hydrides in MeCN are estimated for the first time using the ligand acidity constant (LAC) equation where contributions to the pKaMeCN from each ligand are simply added together, with the sum corrected for effects of charge and 5d metals. The pKaLAC-MeCN([MHLn]+/MLn) of over 200 hydride complexes MHLn are used, along with their electrochemical potentials from the literature, in an uncommonly applied thermochemical cycle in order to reveal systematic trends in the redox couples MIII/II and MV/IV (M = Cr, Mo, W), MnII/I, ReVI/V and ReIV/III, MIII/II and MIV/III (M = Fe, Ru, Os), and MIII/II and MII/I (M = Co, Rh, and Ir) and allow the estimation of the bond dissociation free energies BDFE(MH) of the unoxidized hydrides MHLn and the prediction of the electrochemical potential for their oxidation. Density functional theory (DFT) calculations are used to validate the pKaLAC-MeCN values of hydrides of WIII, MnII, FeIII, RuIII, CoII, and NiIII. When a pKaLAC-MeCN is less than zero for a given complex [MHLn]+, the oxidation of MHLn is irreversible due to proton loss from the oxidized complex to the solvent. When pKaLAC-MeCN ≫ 0, the oxidation is reversible when there is no gross change in the coordination geometry upon a change in the redox state. Twenty paramagnetic hydrides prepared in bulk all have pKaLAC-MeCN > 8.
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Affiliation(s)
- Benjamin E Rennie
- Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S3H6, Canada
| | - Renée G Eleftheriades
- Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S3H6, Canada
| | - Robert H Morris
- Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S3H6, Canada
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16
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Salvadori E, Chiesa M, Buonerba A, Grassi A. Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization. Chem Sci 2020; 11:12436-12445. [PMID: 34123229 PMCID: PMC8162776 DOI: 10.1039/d0sc04967k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 09/24/2020] [Indexed: 11/29/2022] Open
Abstract
Metal hydride complexes find widespread application in catalysis and their properties are often understood on the basis of the available crystal structures. However, some catalytically relevant metal hydrides are only spontaneously formed in situ, cannot be isolated in large quantities or crystallised and their structure is therefore ill defined. One such example is the paramagnetic Ti(iii)-hydride involved in homogeneous Ziegler-Natta catalysis, formed upon activation of CpTi(iv)Cl3 with modified methylalumoxane (MMAO). In this contribution, through a combined use of electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopies we identify the nature of the ligands, their bonding interaction and the extent of the spin distribution. From the data, an atomistic and electronic model is proposed, which supports the presence of a self-assembled ion pair between a cationic terminal Ti-hydride and an aluminate anion, with a hydrodynamic radius of ca. 16 Å.
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Affiliation(s)
- Enrico Salvadori
- Department of Chemistry, University of Turin Via Pietro Giuria 7 Torino 10125 Italy
| | - Mario Chiesa
- Department of Chemistry, University of Turin Via Pietro Giuria 7 Torino 10125 Italy
| | - Antonio Buonerba
- Dipartimento di Chimica e Biologia, Università degli Studi di Salerno Via Giovanni Paolo II, 132 I-84084 Fisciano SA Italy
| | - Alfonso Grassi
- Dipartimento di Chimica e Biologia, Università degli Studi di Salerno Via Giovanni Paolo II, 132 I-84084 Fisciano SA Italy
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17
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Reiners M, Baabe D, Münster K, Zaretzke MK, Freytag M, Jones PG, Coppel Y, Bontemps S, Rosal ID, Maron L, Walter MD. NH 3 formation from N 2 and H 2 mediated by molecular tri-iron complexes. Nat Chem 2020; 12:740-746. [PMID: 32601410 DOI: 10.1038/s41557-020-0483-7] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 05/05/2020] [Indexed: 01/27/2023]
Abstract
Living systems carry out the reduction of N2 to ammonia (NH3) through a series of protonation and electron transfer steps under ambient conditions using the enzyme nitrogenase. In the chemical industry, the Haber-Bosch process hydrogenates N2 but requires high temperatures and pressures. Both processes rely on iron-based catalysts, but molecular iron complexes that promote the formation of NH3 on addition of H2 to N2 have remained difficult to devise. Here, we isolate the tri(iron)bis(nitrido) complex [(Cp'Fe)3(μ3-N)2] (in which Cp' = η5-1,2,4-(Me3C)3C5H2), which is prepared by reduction of [Cp'Fe(μ-I)]2 under an N2 atmosphere and comprises three iron centres bridged by two μ3-nitrido ligands. In solution, this complex reacts with H2 at ambient temperature (22 °C) and low pressure (1 or 4 bar) to form NH3. In the solid state, it is converted into the tri(iron)bis(imido) species, [(Cp'Fe)3(μ3-NH)2], by addition of H2 (10 bar) through an unusual solid-gas, single-crystal-to-single-crystal transformation. In solution, [(Cp'Fe)3(μ3-NH)2] further reacts with H2 or H+ to form NH3.
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Affiliation(s)
- Matthias Reiners
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany
| | - Dirk Baabe
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany
| | - Katharina Münster
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany
| | - Marc-Kevin Zaretzke
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany
| | - Matthias Freytag
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany
| | - Peter G Jones
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany
| | - Yannick Coppel
- CNRS, LCC (Laboratoire de Chimie de Coordination), Université de Toulouse, UPS, INPT, Toulouse, France
| | - Sébastien Bontemps
- CNRS, LCC (Laboratoire de Chimie de Coordination), Université de Toulouse, UPS, INPT, Toulouse, France
| | - Iker Del Rosal
- Université de Toulouse, INSA-UPS-LPCNO and CNRS-LPCNO, Toulouse, France
| | - Laurent Maron
- Université de Toulouse, INSA-UPS-LPCNO and CNRS-LPCNO, Toulouse, France
| | - Marc D Walter
- Technische Universität Braunschweig, Institut für Anorganische und Analytische Chemie, Braunschweig, Germany.
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18
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Lohrey TD, Fostvedt JI, Bergman RG, Arnold J. Electron acceptors promote proton–hydride tautomerism in low valent rhenium β-diketiminates. Chem Commun (Camb) 2020; 56:3761-3764. [DOI: 10.1039/c9cc09475j] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a series of β-diketiminate (BDI) complexes in which tautomeric rhenium(iii) hydride and rhenium(i) protio-BDI species readily interconvert between the solid and solution states.
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Affiliation(s)
- Trevor D. Lohrey
- Department of Chemistry
- University of California
- Berkeley
- USA
- Chemical Sciences Division
| | | | | | - John Arnold
- Department of Chemistry
- University of California
- Berkeley
- USA
- Chemical Sciences Division
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