1
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White NM, Waldie KM. Electrocatalytic formate and alcohol oxidation by hydride transfer at first-row transition metal complexes. Dalton Trans 2024. [PMID: 38896286 DOI: 10.1039/d3dt04304e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
The electrocatalytic oxidation of carbon-based liquid fuels, such as formic acid and alcohols, has important applications for our renewable energy transition. Molecular electrocatalysts based on transition metal complexes provide the opportunity to explore the interplay between precise catalyst design and electrocatalytic activity. Recent advances have seen the development of first-row transition metal electrocatalysts for these transformations that operate via hydride transfer between the substrate and catalyst. In this Frontier article, we present the key contributions to this field and discuss the proposed mechanisms for each case. These studies also reveal the remaining challenges for formate and alcohol oxidation with first-row transition metal systems, for which we provide perspectives on future directions for next-generation electrocatalyst design.
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Affiliation(s)
- Navar M White
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 123 Bevier Road, Piscataway, New Jersey 08854, USA.
| | - Kate M Waldie
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 123 Bevier Road, Piscataway, New Jersey 08854, USA.
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2
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Huang KY, Yang ZQ, Yang MR, Chen TS, Tang S, Sun WM, Yao Q, Deng HH, Chen W, Xie J. Unraveling a Concerted Proton-Coupled Electron Transfer Pathway in Atomically Precise Gold Nanoclusters. J Am Chem Soc 2024; 146:8706-8715. [PMID: 38487838 DOI: 10.1021/jacs.4c01180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/28/2024]
Abstract
Metal nanoclusters (MNCs) represent a promising class of materials for catalytic carbon dioxide and proton reduction as well as dihydrogen oxidation. In such reactions, multiple proton-coupled electron transfer (PCET) processes are typically involved, and the current understanding of PCET mechanisms in MNCs has primarily focused on the sequential transfer mode. However, a concerted transfer pathway, i.e., concerted electron-proton transfer (CEPT), despite its potential for a higher catalytic rate and lower reaction barrier, still lacks comprehensive elucidation. Herein, we introduce an experimental paradigm to test the feasibility of the CEPT process in MNCs, by employing Au18(SR)14 (SR denotes thiolate ligand), Au22(SR)18, and Au25(SR)18- as model clusters. Detailed investigations indicate that the photoinduced PCET reactions in the designed system proceed via an CEPT pathway. Furthermore, the rate constants of gold nanoclusters (AuNCs) have been found to be correlated with both the size of the cluster and the flexibility of the Au-S framework. This newly identified PCET behavior in AuNCs is prominently different from that observed in semiconductor quantum dots and plasmonic metal nanoparticles. Our findings are of crucial importance for unveiling the catalytic mechanisms of quantum-confined metal nanomaterials and for the future rational design of more efficient catalysts.
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Affiliation(s)
- Kai-Yuan Huang
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Zhi-Qiang Yang
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Ming-Rui Yang
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Tian-Shui Chen
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Shurong Tang
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Wei-Ming Sun
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Qiaofeng Yao
- Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Key Laboratory of Organic Integrated Circuits, Ministry of Education, Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China
| | - Hao-Hua Deng
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Wei Chen
- Higher Educational Key Laboratory for Nano Biomedical Technology of Fujian Province, Department of Pharmaceutical Analysis, Fujian Medical University, Fuzhou 350004, China
| | - Jianping Xie
- Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117585, Singapore
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3
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Lewis NB, Bisbey RP, Westendorff KS, Soudackov AV, Surendranath Y. A molecular-level mechanistic framework for interfacial proton-coupled electron transfer kinetics. Nat Chem 2024; 16:343-352. [PMID: 38228851 DOI: 10.1038/s41557-023-01400-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Accepted: 11/15/2023] [Indexed: 01/18/2024]
Abstract
Electrochemical proton-coupled electron transfer (PCET) reactions can proceed via an outer-sphere electron transfer to solution (OS-PCET) or through an inner-sphere mechanism by interfacial polarization of surface-bound active sites (I-PCET). Although OS-PCET has been extensively studied with molecular insight, the inherent heterogeneity of surfaces impedes molecular-level understanding of I-PCET. Herein we employ graphite-conjugated carboxylic acids (GC-COOH) as molecularly well-defined hosts of I-PCET to isolate the intrinsic kinetics of I-PCET. We measure I-PCET rates across the entire pH range, uncovering a V-shaped pH-dependence that lacks the pH-independent regions characteristic of OS-PCET. Accordingly, we develop a mechanistic model for I-PCET that invokes concerted PCET involving hydronium/water or water/hydroxide donor/acceptor pairs, capturing the entire dataset with only four adjustable parameters. We find that I-PCET is fourfold faster with hydronium/water than water/hydroxide, while both reactions display similarly high charge transfer coefficients, indicating late proton transfer transition states. These studies highlight the key mechanistic distinctions between I-PCET and OS-PCET, providing a framework for understanding and modelling more complex multistep I-PCET reactions critical to energy conversion and catalysis.
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Affiliation(s)
- Noah B Lewis
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Ryan P Bisbey
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Karl S Westendorff
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Yogesh Surendranath
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
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4
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Cooney S, Walls MRA, Schreiber E, Brennessel WW, Matson EM. Heterometal Dopant Changes the Mechanism of Proton-Coupled Electron Transfer at the Polyoxovanadate-Alkoxide Surface. J Am Chem Soc 2024; 146:2364-2369. [PMID: 38241170 PMCID: PMC10835708 DOI: 10.1021/jacs.3c14054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 01/11/2024] [Accepted: 01/12/2024] [Indexed: 01/21/2024]
Abstract
The transfer of two H-atom equivalents to the titanium-doped polyoxovanadate-alkoxide, [TiV5O6(OCH3)13], results in the formation of a V(III)-OH2 site at the surface of the assembly. Incorporation of the group (IV) metal ion results in a weakening of the O-H bonds of [TiV5O5(OH2)(OCH3)13] in comparison to its homometallic congener, [V6O6(OH2)(OCH3)12], resembling more closely the thermodynamics reported for the one-electron reduced derivative, [V6O6(OH2)(OCH3)12]1-. An analysis of early time points of the reaction of [TiV5O6(OCH3)13] and 5,10-dihydrophenazine reveals the formation of an oxidized substrate, suggesting that proton-coupled electron transfer proceeds via initial electron transfer from substrate to cluster prior to proton transfer. These results demonstrate the profound influence of heterometal dopants on the mechanism of PCET with respect to the surface of the assembly.
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Affiliation(s)
- Shannon
E. Cooney
- Department of Chemistry, University
of Rochester, Rochester, New York 14627, United States
| | - M. Rebecca A. Walls
- Department of Chemistry, University
of Rochester, Rochester, New York 14627, United States
| | - Eric Schreiber
- Department of Chemistry, University
of Rochester, Rochester, New York 14627, United States
| | - William W. Brennessel
- Department of Chemistry, University
of Rochester, Rochester, New York 14627, United States
| | - Ellen M. Matson
- Department of Chemistry, University
of Rochester, Rochester, New York 14627, United States
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5
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Wang Y, Ge X, Lu Q, Bai W, Ye C, Shao Z, Bu Y. Accelerated deprotonation with a hydroxy-silicon alkali solid for rechargeable zinc-air batteries. Nat Commun 2023; 14:6968. [PMID: 37907458 PMCID: PMC10618233 DOI: 10.1038/s41467-023-42728-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Accepted: 10/20/2023] [Indexed: 11/02/2023] Open
Abstract
Transition metal oxides are promising electrocatalysts for zinc-air batteries, yet surface reconstruction caused by the adsorbate evolution mechanism, which induces zinc-ion battery behavior in the oxygen evolution reaction, leads to poor cycling performance. In this study, we propose a lattice oxygen mechanism involving proton acceptors to overcome the poor performance of the battery in the OER process. We introduce a stable solid base, hydroxy BaCaSiO4, onto the surfaces of PrBa0.5Ca0.5Co2O5+δ perovskite nanofibers with a one-step exsolution strategy. The HO-Si sites on the hydroxy BaCaSiO4 significantly accelerate proton transfer from the OH* adsorbed on PrBa0.5Ca0.5Co2O5+δ during the OER process. As a proof of concept, a rechargeable zinc-air battery assembled with this composite electrocatalyst is stable in an alkaline environment for over 150 hours at 5 mA cm-2 during galvanostatic charge/discharge tests. Our findings open new avenues for designing efficient OER electrocatalysts for rechargeable zinc-air batteries.
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Affiliation(s)
- Yaobin Wang
- Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, UNIST-NUIST Energy and Environment Jointed Lab, (UNNU), School of Environmental Science and Technology, Nanjing University of Information Science and Technology (NUIST), 219 Ningliu, Nanjing, 210044, P. R. China
| | - Xinlei Ge
- Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, UNIST-NUIST Energy and Environment Jointed Lab, (UNNU), School of Environmental Science and Technology, Nanjing University of Information Science and Technology (NUIST), 219 Ningliu, Nanjing, 210044, P. R. China
| | - Qian Lu
- Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, UNIST-NUIST Energy and Environment Jointed Lab, (UNNU), School of Environmental Science and Technology, Nanjing University of Information Science and Technology (NUIST), 219 Ningliu, Nanjing, 210044, P. R. China.
| | - Wenjun Bai
- Academy for Advanced Interdisciplinary Studies & Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Caichao Ye
- Academy for Advanced Interdisciplinary Studies & Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China.
| | - Zongping Shao
- WA School of Mines: Minerals, Energy and Chemical Engineering (WASM-MECE), Curtin University, Perth, WA, 6845, Australia.
| | - Yunfei Bu
- Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, UNIST-NUIST Energy and Environment Jointed Lab, (UNNU), School of Environmental Science and Technology, Nanjing University of Information Science and Technology (NUIST), 219 Ningliu, Nanjing, 210044, P. R. China.
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6
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Zhao N, Goetz MK, Schneider JE, Anderson JS. Testing the Limits of Imbalanced CPET Reactivity: Mechanistic Crossover in H-Atom Abstraction by Co(III)-Oxo Complexes. J Am Chem Soc 2023; 145:5664-5673. [PMID: 36867838 PMCID: PMC10023487 DOI: 10.1021/jacs.2c10553] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
Abstract
Transition metal-oxo complexes are key intermediates in a variety of oxidative transformations, notably C-H bond activation. The relative rate of C-H bond activation mediated by transition metal-oxo complexes is typically predicated on substrate bond dissociation free energy in cases with a concerted proton-electron transfer (CPET). However, recent work has demonstrated that alternative stepwise thermodynamic contributions such as acidity/basicity or redox potentials of the substrate/metal-oxo may dominate in some cases. In this context, we have found basicity-governed concerted activation of C-H bonds with the terminal CoIII-oxo complex PhB(tBuIm)3CoIIIO. We have been interested in testing the limits of such basicity-dependent reactivity and have synthesized an analogous, more basic complex, PhB(AdIm)3CoIIIO, and studied its reactivity with H-atom donors. This complex displays a higher degree of imbalanced CPET reactivity than PhB(tBuIm)3CoIIIO with C-H substrates, and O-H activation of phenol substrates displays mechanistic crossover to stepwise proton transfer-electron transfer (PTET) reactivity. Analysis of the thermodynamics of proton transfer (PT) and electron transfer (ET) reveals a distinct thermodynamic crossing point between concerted and stepwise reactivity. Furthermore, the relative rates of stepwise and concerted reactivity suggest that maximally imbalanced systems provide the fastest CPET rates up to the point of mechanistic crossover, which results in slower product formation.
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Affiliation(s)
- Norman Zhao
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | | | - Joseph E. Schneider
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
| | - John S. Anderson
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States
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7
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Schreiber E, Brennessel WW, Matson EM. Regioselectivity of concerted proton-electron transfer at the surface of a polyoxovanadate cluster. Chem Sci 2023; 14:1386-1396. [PMID: 36794190 PMCID: PMC9906639 DOI: 10.1039/d2sc05928b] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 12/19/2022] [Indexed: 01/19/2023] Open
Abstract
Proton-coupled electron transfer (PCET) is an important process in the activation and reactivity of metal oxide surfaces. In this work, we study the electronic structure of a reduced polyoxovanadate-alkoxide cluster bearing a single bridging oxide moiety. The structural and electronic implications of the incorporation of bridging oxide sites are revealed, most notably resulting in the quenching of cluster-wide electron delocalization in the most reduced state of the molecule. We correlate this attribute to a change in regioselectivity of PCET to the cluster surface (e.g. reactivity at terminal vs. bridging oxide groups). Reactivity localized at the bridging oxide site enables reversible storage of a single H-atom equivalent, changing the stoichiometry of PCET from a 2e-/2H+ process. Kinetic investigations indicate that the change in site of reactivity translates to an accelerated rate of e-/H+ transfer to the cluster surface. Our work summarizes the role which electronic occupancy and ligand density play in the uptake of e-/H+ pairs at metal oxide surfaces, providing design criteria for functional materials for energy storage and conversion processes.
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Affiliation(s)
- Eric Schreiber
- Department of Chemistry, University of Rochester Rochester NY 14611 USA
| | | | - Ellen M Matson
- Department of Chemistry, University of Rochester Rochester NY 14611 USA
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8
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Neyrizi S, Kiewiet J, Hempenius MA, Mul G. What It Takes for Imidazolium Cations to Promote Electrochemical Reduction of CO 2. ACS ENERGY LETTERS 2022; 7:3439-3446. [PMID: 36277133 PMCID: PMC9578038 DOI: 10.1021/acsenergylett.2c01372] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 09/06/2022] [Indexed: 06/16/2023]
Abstract
Imidazolium cations enhance the performance of several electrodes in converting CO2 to CO in non-aqueous media. In this publication, we elucidate the origin of the function of imidazolium cations when exposed to Au electrodes in anhydrous acetonitrile in CO2 atmosphere. We demonstrate that imidazolium cations lead to unprecedentedly low overpotentials for CO2 reduction to CO on Au, with ∼100% Faradaic efficiency. By modification of the N1 and N3 functionality of the imidazolium cation, we show a direct correlation between the performance in CO2 reduction and the C2-H acidity of the cation. Based on NMR analyses, DFT calculations, and isotopic labeling, showing an inverse kinetic isotope effect, we demonstrate that the mechanism involves a concerted proton-electron transfer to the electrode-adsorbed CO2 intermediate. The demonstrated mechanism provides guidelines for improvement in the energy efficiency of non-aqueous electrochemical CO2 reduction, by a tailored design of electrolyte cations.
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Affiliation(s)
- Sobhan Neyrizi
- Photocatalytic
Synthesis Group, Faculty of Science & Technology, University of Twente, P.O. Box 217, Enschede 7500 AE, The
Netherlands
- Sustainable
Polymer Chemistry, Faculty of Science & Technology, University of Twente, P.O. Box 217, Enschede 7500 AE, The Netherlands
| | - Joep Kiewiet
- Photocatalytic
Synthesis Group, Faculty of Science & Technology, University of Twente, P.O. Box 217, Enschede 7500 AE, The
Netherlands
| | - Mark A. Hempenius
- Sustainable
Polymer Chemistry, Faculty of Science & Technology, University of Twente, P.O. Box 217, Enschede 7500 AE, The Netherlands
| | - Guido Mul
- Photocatalytic
Synthesis Group, Faculty of Science & Technology, University of Twente, P.O. Box 217, Enschede 7500 AE, The
Netherlands
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9
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Nilsen-Moe A, Rosichini A, Glover SD, Hammarström L. Concerted and Stepwise Proton-Coupled Electron Transfer for Tryptophan-Derivative Oxidation with Water as the Primary Proton Acceptor: Clarifying a Controversy. J Am Chem Soc 2022; 144:7308-7319. [PMID: 35416654 PMCID: PMC9052761 DOI: 10.1021/jacs.2c00371] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Concerted electron-proton transfer (CEPT) reactions avoid charged intermediates and may be energetically favorable for redox and radical-transfer reactions in natural and synthetic systems. Tryptophan (W) often partakes in radical-transfer chains in nature but has been proposed to only undergo sequential electron transfer followed by proton transfer when water is the primary proton acceptor. Nevertheless, our group has shown that oxidation of freely solvated tyrosine and W often exhibit weakly pH-dependent proton-coupled electron transfer (PCET) rate constants with moderate kinetic isotope effects (KIE ≈ 2-5), which could be associated with a CEPT mechanism. These results and conclusions have been questioned. Here, we present PCET rate constants for W derivatives with oxidized Ru- and Zn-porphyrin photosensitizers, extracted from laser flash-quench studies. Alternative quenching/photo-oxidation methods were used to avoid complications of previous studies, and both the amine and carboxylic acid groups of W were protected to make the indole the only deprotonable group. With a suitably tuned oxidant strength, we found an ET-limited reaction at pH < 4 and weakly pH-dependent rates at pH > ∼5 that are intrinsic to the PCET of the indole group with water (H2O) as the proton acceptor. The observed rate constants are up to more than 100 times higher than those measured for initial electron transfer, excluding the electron-first mechanism. Instead, the reaction can be attributed to CEPT. These conclusions are important for our view of CEPT in water and of PCET-mediated radical reactions with solvent-exposed tryptophan in natural systems.
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Affiliation(s)
- Astrid Nilsen-Moe
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
| | - Andrea Rosichini
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
| | - Starla D Glover
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratory, Uppsala University, P.O. Box 523, 75120 Uppsala, Sweden
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10
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Murray PD, Cox JH, Chiappini ND, Roos CB, McLoughlin EA, Hejna BG, Nguyen ST, Ripberger HH, Ganley JM, Tsui E, Shin NY, Koronkiewicz B, Qiu G, Knowles RR. Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis. Chem Rev 2022; 122:2017-2291. [PMID: 34813277 PMCID: PMC8796287 DOI: 10.1021/acs.chemrev.1c00374] [Citation(s) in RCA: 147] [Impact Index Per Article: 73.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Indexed: 12/16/2022]
Abstract
We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.
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Affiliation(s)
- Philip
R. D. Murray
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - James H. Cox
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Nicholas D. Chiappini
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Casey B. Roos
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | | | - Benjamin G. Hejna
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Suong T. Nguyen
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Hunter H. Ripberger
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Jacob M. Ganley
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Elaine Tsui
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Nick Y. Shin
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Brian Koronkiewicz
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Guanqi Qiu
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
| | - Robert R. Knowles
- Department of Chemistry, Princeton
University, Princeton, New Jersey 08544, United States
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11
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Novaes LFT, Ho JSK, Mao K, Liu K, Tanwar M, Neurock M, Villemure E, Terrett JA, Lin S. Exploring Electrochemical C(sp 3)-H Oxidation for the Late-Stage Methylation of Complex Molecules. J Am Chem Soc 2022; 144:1187-1197. [PMID: 35015533 DOI: 10.1021/jacs.1c09412] [Citation(s) in RCA: 48] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The "magic methyl" effect, a dramatic boost in the potency of biologically active compounds from the incorporation of a single methyl group, provides a simple yet powerful strategy employed by medicinal chemists in the drug discovery process. Despite significant advances, methodologies that enable the selective C(sp3)-H methylation of structurally complex medicinal agents remain very limited. In this work, we disclose a modular, efficient, and selective strategy for the α-methylation of protected amines (i.e., amides, carbamates, and sulfonamides) by means of electrochemical oxidation. Mechanistic analysis guided our development of an improved electrochemical protocol on the basis of the classic Shono oxidation reaction, which features broad reaction scope, high functional group compatibility, and operational simplicity. Importantly, this reaction system is amenable to the late-stage functionalization of complex targets containing basic nitrogen groups that are prevalent in medicinally active agents. When combined with organozinc-mediated C-C bond formation, our protocol enabled the direct methylation of a myriad of amine derivatives including those that have previously been explored for the "magic methyl" effect. This synthesis strategy thus circumvents multistep de novo synthesis that is currently necessary to access such compounds and has the potential to accelerate drug discovery efforts.
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Affiliation(s)
- Luiz F T Novaes
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14850, United States
| | - Justin S K Ho
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14850, United States
| | - Kaining Mao
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14850, United States
| | - Kaida Liu
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Mayank Tanwar
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Matthew Neurock
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Elisia Villemure
- Department of Discovery Chemistry, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States
| | - Jack A Terrett
- Department of Discovery Chemistry, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States
| | - Song Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14850, United States
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12
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Kim S, Choi J, Cho DW, Ahn M, Eom S, Kim J, Wee KR, Ihee H. Solvent-modulated proton-coupled electron transfer in an iridium complex with an ESIPT ligand. Chem Sci 2022; 13:3809-3818. [PMID: 35432886 PMCID: PMC8966730 DOI: 10.1039/d1sc07250a] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Accepted: 03/03/2022] [Indexed: 11/21/2022] Open
Abstract
Proton-coupled electron transfer (PCET), an essential process in nature with a well-known example of photosynthesis, has recently been employed in metal complexes to improve the energy conversion efficiency; however, a profound understanding of the mechanism of PCET in metal complexes is still lacking. In this study, we synthesized cyclometalated Ir complexes strategically designed to exploit the excited-state intramolecular proton transfer (ESIPT) of the ancillary ligand and studied their photoinduced PCET in both aprotic and protic solvent environments using femtosecond transient absorption spectroscopy and density functional theory (DFT) and time-dependent DFT calculations. The data reveal solvent-modulated PCET, where charge transfer follows proton transfer in an aprotic solvent and the temporal order of charge transfer and proton transfer is reversed in a protic solvent. In the former case, ESIPT from the enol form to the keto form, which precedes the charge transfer from Ir to the ESIPT ligand, improves the efficiency of metal-to-ligand charge transfer. This finding demonstrates the potential to control the PCET reaction in the desired direction and the efficiency of charge transfer by simply perturbing the external hydrogen-bonding network with the solvent. The iridium complex with an ESIPT ligand shows solvent-modulated proton-coupled electron transfer, in which the temporal order of proton transfer and charge transfer is altered by the solvent environment.![]()
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Affiliation(s)
- Siin Kim
- Department of Chemistry and KI for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
- Center for Advanced Reaction Dynamics, Institute for Basic Science Daejeon 34141 Republic of Korea
| | - Jungkweon Choi
- Department of Chemistry and KI for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
- Center for Advanced Reaction Dynamics, Institute for Basic Science Daejeon 34141 Republic of Korea
| | - Dae Won Cho
- Department of Advanced Materials Chemistry, Korea University, Sejong Campus Sejong 30019 Korea
| | - Mina Ahn
- Department of Chemistry and Institute of Natural Science, Daegu University Gyeongsan 38453 Republic of Korea
| | - Seunghwan Eom
- Department of Chemistry and KI for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
- Center for Advanced Reaction Dynamics, Institute for Basic Science Daejeon 34141 Republic of Korea
| | - Jungmin Kim
- Department of Chemistry and KI for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
- Center for Advanced Reaction Dynamics, Institute for Basic Science Daejeon 34141 Republic of Korea
| | - Kyung-Ryang Wee
- Department of Chemistry and Institute of Natural Science, Daegu University Gyeongsan 38453 Republic of Korea
| | - Hyotcherl Ihee
- Department of Chemistry and KI for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Republic of Korea
- Center for Advanced Reaction Dynamics, Institute for Basic Science Daejeon 34141 Republic of Korea
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13
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Tyburski R, Hammarström L. Strategies for switching the mechanism of proton-coupled electron transfer reactions illustrated by mechanistic zone diagrams. Chem Sci 2022; 13:290-301. [PMID: 35059179 PMCID: PMC8694376 DOI: 10.1039/d1sc05230f] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Accepted: 11/26/2021] [Indexed: 12/19/2022] Open
Abstract
The mechanism by which proton-coupled electron transfer (PCET) occurs is of fundamental importance and has great consequences for applications, e.g. in catalysis. However, determination and tuning of the PCET mechanism is often non-trivial. Here, we apply mechanistic zone diagrams to illustrate the competition between concerted and stepwise PCET-mechanisms in the oxidation of 4-methoxyphenol by Ru(bpy)33+-derivatives in the presence of substituted pyridine bases. These diagrams show the dominating mechanism as a function of driving force for electron and proton transfer (ΔG0ET and ΔG0PT) respectively [Tyburski et al., J. Am. Chem. Soc., 2021, 143, 560]. Within this framework, we demonstrate strategies for mechanistic tuning, namely balancing of ΔG0ET and ΔG0PT, steric hindrance of the proton-transfer coordinate, and isotope substitution. Sterically hindered pyridine bases gave larger reorganization energy for concerted PCET, resulting in a shift towards a step-wise electron first-mechanism in the zone diagrams. For cases when sufficiently strong oxidants are used, substitution of protons for deuterons leads to a switch from concerted electron–proton transfer (CEPT) to an electron transfer limited (ETPTlim) mechanism. We thereby, for the first time, provide direct experimental evidence, that the vibronic coupling strength affects the switching point between CEPT and ETPTlim, i.e. at what driving force one or the other mechanism starts dominating. Implications for solar fuel catalysis are discussed. The mechanism by which proton-coupled electron transfer (PCET) occurs is of fundamental importance and has great consequences for applications, e.g. in catalysis.![]()
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Affiliation(s)
- Robin Tyburski
- Department of Chemistry – Ångström Laboratory, Uppsala University, Box 532, SE75120 Uppsala, Sweden
| | - Leif Hammarström
- Department of Chemistry – Ångström Laboratory, Uppsala University, Box 532, SE75120 Uppsala, Sweden
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14
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Agarwal RG, Coste SC, Groff BD, Heuer AM, Noh H, Parada GA, Wise CF, Nichols EM, Warren JJ, Mayer JM. Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications. Chem Rev 2021; 122:1-49. [PMID: 34928136 DOI: 10.1021/acs.chemrev.1c00521] [Citation(s) in RCA: 126] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We present an update and revision to our 2010 review on the topic of proton-coupled electron transfer (PCET) reagent thermochemistry. Over the past decade, the data and thermochemical formalisms presented in that review have been of value to multiple fields. Concurrently, there have been advances in the thermochemical cycles and experimental methods used to measure these values. This Review (i) summarizes those advancements, (ii) corrects systematic errors in our prior review that shifted many of the absolute values in the tabulated data, (iii) provides updated tables of thermochemical values, and (iv) discusses new conclusions and opportunities from the assembled data and associated techniques. We advocate for updated thermochemical cycles that provide greater clarity and reduce experimental barriers to the calculation and measurement of Gibbs free energies for the conversion of X to XHn in PCET reactions. In particular, we demonstrate the utility and generality of reporting potentials of hydrogenation, E°(V vs H2), in almost any solvent and how these values are connected to more widely reported bond dissociation free energies (BDFEs). The tabulated data demonstrate that E°(V vs H2) and BDFEs are generally insensitive to the nature of the solvent and, in some cases, even to the phase (gas versus solution). This Review also presents introductions to several emerging fields in PCET thermochemistry to give readers windows into the diversity of research being performed. Some of the next frontiers in this rapidly growing field are coordination-induced bond weakening, PCET in novel solvent environments, and reactions at material interfaces.
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Affiliation(s)
- Rishi G Agarwal
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Scott C Coste
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Benjamin D Groff
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Abigail M Heuer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Hyunho Noh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Giovanny A Parada
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.,Department of Chemistry, The College of New Jersey, Ewing, New Jersey 08628, United States
| | - Catherine F Wise
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Eva M Nichols
- Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Jeffrey J Warren
- Department of Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
| | - James M Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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15
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He S, Huang F, Wu Q, Zhang P, Xiong Y, Yang J, Zhang R, Wang F, Chen L, Liu TL, Li F. Multiple‐Site Concerted Proton–Electron Transfer in a Manganese‐Based Complete Functional Model for [FeFe]‐Hydrogenase. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202106983] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Shuanglin He
- State Key Laboratory of Environment-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
| | - Fang Huang
- College of Chemistry, Chemical Engineering and Materials Science Shandong Normal University Jinan 250014 P. R. China
| | - Qianqian Wu
- State Key Laboratory of Environment-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
| | - Ping Zhang
- State Key Laboratory of Environment-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
| | - Ying Xiong
- State Key Laboratory of Environment-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
| | - Jie Yang
- State Key Laboratory of Environment-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
| | - Rong Zhang
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116024 P. R. China
| | - Fang Wang
- Department of Chemistry and Biochemistry Utah State University College of Chemistry Logan Utah 84318 USA
| | - Lin Chen
- State Key Laboratory of Environment-Friendly Energy Materials School of Materials Science and Engineering Southwest University of Science and Technology Mianyang 621010 P. R. China
| | - T. Leo Liu
- Department of Chemistry and Biochemistry Utah State University College of Chemistry Logan Utah 84318 USA
| | - Fei Li
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116024 P. R. China
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16
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He S, Huang F, Wu Q, Zhang P, Xiong Y, Yang J, Zhang R, Wang F, Chen L, Liu TL, Li F. Multiple-Site Concerted Proton-Electron Transfer in a Manganese-Based Complete Functional Model for [FeFe]-Hydrogenase. Angew Chem Int Ed Engl 2021; 60:25839-25845. [PMID: 34595813 DOI: 10.1002/anie.202106983] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Indexed: 11/10/2022]
Abstract
The active site of [FeFe]-hydrogenase (H2 ase) is preorganized with an amine (azadithiolate) as a proton relay and a [4Fe4S] subunit as an electron reservoir, which together lower the overpotential for proton reduction and hydrogen oxidation by multiple-site concerted proton-electron transfer (MS-CPET). Herein, we report a mononuclear manganese complex, fac-[Mn(CO)3 (6-(2-hydroxyphenol)-2-pyridine-2-quinoline) Br] (1), as a rare model to fully mimic the functions of the H2 ase. In 1, a redox-active bidentate ligand with a pendent phenol replicates the roles of the electron reservoir and the proton relay in the enzyme. Experimental and theoretical studies revealed two consecutive MS-CPET processes in the catalytic cycle, in each of which an electron stored in the reductive ligand and a proton at the proximal phenol moiety are transferred to the Mn center in a concerted way. By virtue of this mechanism, complex 1 exhibited a low overpotential comparable to that of natural enzyme in electrochemical hydrogen production using phenol as a proton source.
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Affiliation(s)
- Shuanglin He
- State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China
| | - Fang Huang
- College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan, 250014, P. R. China
| | - Qianqian Wu
- State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China
| | - Ping Zhang
- State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China
| | - Ying Xiong
- State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China
| | - Jie Yang
- State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China
| | - Rong Zhang
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, P. R. China
| | - Fang Wang
- Department of Chemistry and Biochemistry, Utah State University College of Chemistry, Logan, Utah, 84318, USA
| | - Lin Chen
- State Key Laboratory of Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China
| | - T Leo Liu
- Department of Chemistry and Biochemistry, Utah State University College of Chemistry, Logan, Utah, 84318, USA
| | - Fei Li
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, P. R. China
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17
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Coste SC, Brezny AC, Koronkiewicz B, Mayer JM. C-H oxidation in fluorenyl benzoates does not proceed through a stepwise pathway: revisiting asynchronous proton-coupled electron transfer. Chem Sci 2021; 12:13127-13136. [PMID: 34745543 PMCID: PMC8513817 DOI: 10.1039/d1sc03344a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Accepted: 09/09/2021] [Indexed: 11/21/2022] Open
Abstract
2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant. Kinetic analysis revealed unusual rate-driving force relationships. Our analysis indicated a mechanism of multi-site concerted proton–electron transfer (MS-CPET) for all of these reactions. More recently, an alternative interpretation of the kinetic data was proposed to explain the unusual rate-driving force relationships, invoking a crossover from CPET to a stepwise mechanism with an initial intramolecular proton transfer (PT) (Costentin, Savéant, Chem. Sci., 2020, 11, 1006). Here, we show that this proposed alternative pathway is untenable based on prior and new experimental assessments of the intramolecular PT equilibrium constant and rates. Measurement of the fluorenyl 9-C–H pKa, H/D exchange experiments, and kinetic modelling with COPASI eliminate the possibility of a stepwise mechanism for C–H oxidation in the fluorenyl benzoate series. Implications for asynchronous (imbalanced) MS-CPET mechanisms are discussed with respect to classical Marcus theory and the quantum-mechanical treatment of concerted proton–electron transfer. 2-Fluorenyl benzoates were recently shown to undergo C–H bond oxidation through intramolecular proton transfer coupled with electron transfer to an external oxidant.![]()
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Affiliation(s)
- Scott C Coste
- Department of Chemistry, Yale University New Haven CT 06520-8107 USA
| | - Anna C Brezny
- Department of Chemistry, Skidmore College Saratoga Springs New York 12866 USA
| | | | - James M Mayer
- Department of Chemistry, Yale University New Haven CT 06520-8107 USA
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18
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Hwang D, Schlenker CW. Photochemistry of carbon nitrides and heptazine derivatives. Chem Commun (Camb) 2021; 57:9330-9353. [PMID: 34528956 DOI: 10.1039/d1cc02745j] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We explore the photochemistry of polymeric carbon nitride (C3N4), an archetypal organic photocatalyst, and derivatives of its structural monomer unit, heptazine (Hz). Through spectroscopic studies and computational analysis, we have observed that Hz derivatives can engage in non-innocent hydrogen bonding interactions with hydroxylic species. The photochemistry of these complexes is influenced by intermolecular nπ*/ππ* mixing of non-bonding orbitals of each component and the relative energy of intermolecular charge-transfer (CT) states. Coupling of the former to the latter appears to facilitate proton-coupled electron transfer (PCET), resulting in biradical products. We have also observed that Hz derivatives exhibit an extremely rare inverted singlet/triplet energy splitting (ΔEST). In violation of Hund's multiplicity rules, the lowest energy singlet (S1) is stabilized relative to the lowest triplet (T1) electronic excited state. Exploiting this unique inverted ΔEST character has obvious implications for transformational discoveries in solid-state OLED lighting and photovoltaics. Harnessing this inverted ΔEST, paired with light-driven intermolecular PCET reactions, may enable molecular transformations relevant for applications ranging from solar energy storage to new classes of non-triplet photoredox catalysts for pharmaceutical development. To this end, we have explored the possibility of optically controlling the photochemistry of Hz derivatives using ultrafast pump-push-probe spectroscopy. In this case, the excited state branching ratios among locally excited states of the chromophore and the reactive intermolecular CT state can be manipulated with an appropriate secondary "push" excitation pulse. These results indicate that we can predictively redirect chemical reactivity with light in this system, which is an avidly sought achievement in the field of photochemistry. Looking forward, we anticipate future opportunities for controlling heptazine photochemistry, including manipulating PCET reactivity with a diverse array of substrates and optically delivering reducing equivalents with, for example, water as a partial source of electrons and protons. Furthermore, we wholly expect that, over the next decade, materials such as Hz derivatives, that exhibit inverted ΔEST character, will spawn a significant new research effort in the field of thin-film optoelectronics, where controlling recombination via triplet excitonic states can play a critical role in determining device performance.
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Affiliation(s)
- Doyk Hwang
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| | - Cody W Schlenker
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.,Molecular Engineering & Sciences Institute, University of Washington, Seattle, Washington 98195-1652, USA.,Clean Energy Institute, University of Washington, Seattle, Washington 98195-1653, USA.
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19
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Semiempirical method for examining asynchronicity in metal-oxido-mediated C-H bond activation. Proc Natl Acad Sci U S A 2021; 118:2108648118. [PMID: 34465626 DOI: 10.1073/pnas.2108648118] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The oxidation of substrates via the cleavage of thermodynamically strong C-H bonds is an essential part of mammalian metabolism. These reactions are predominantly carried out by enzymes that produce high-valent metal-oxido species, which are directly responsible for cleaving the C-H bonds. While much is known about the identity of these transient intermediates, the mechanistic factors that enable metal-oxido species to accomplish such difficult reactions are still incomplete. For synthetic metal-oxido species, C-H bond cleavage is often mechanistically described as synchronous, proton-coupled electron transfer (PCET). However, data have emerged that suggest that the basicity of the M-oxido unit is the key determinant in achieving enzymatic function, thus requiring alternative mechanisms whereby proton transfer (PT) has a more dominant role than electron transfer (ET). To bridge this knowledge gap, the reactivity of a monomeric MnIV-oxido complex with a series of external substrates was studied, resulting in a spread of over 104 in their second-order rate constants that tracked with the acidity of the C-H bonds. Mechanisms that included either synchronous PCET or rate-limiting PT, followed by ET, did not explain our results, which led to a proposed PCET mechanism with asynchronous transition states that are dominated by PT. To support this premise, we report a semiempirical free energy analysis that can predict the relative contributions of PT and ET for a given set of substrates. These findings underscore why the basicity of M-oxido units needs to be considered in C-H functionalization.
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20
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Rigodanza F, Marino N, Bonetto A, Marcomini A, Bonchio M, Natali M, Sartorel A. Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated Ru III (bpy) 33+ Oxidant. Chemphyschem 2021; 22:1208-1218. [PMID: 33851772 PMCID: PMC8251842 DOI: 10.1002/cphc.202100190] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 04/13/2021] [Indexed: 02/06/2023]
Abstract
The cobalt substituted polyoxotungstate [Co6 (H2 O)2 (α-B-PW9 O34 )2 (PW6 O26 )]17- (Co6) displays fast electron transfer (ET) kinetics to photogenerated RuIII (bpy)33+ , 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one-electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II)-OH2 and Co6(II)-OH, respectively, whose speciation in aqueous solution is associated to a pKa of 7.6), and generates a Co(III)-OH moiety (Co6(III)-OH), as proven by transient absorption spectroscopy; (ii) at pH>pKa , the Co6(II)-OH→RuIII (bpy)33+ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH
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Affiliation(s)
- Francesco Rigodanza
- Department of Chemical SciencesUniversity of Padovavia Marzolo 135131PadovaItaly
- Consiglio Nazionale delle Ricerche (C.N.R.)Institute on Membrane Technology section of Padovavia Marzolo 135131PadovaItaly
| | - Nadia Marino
- Department of Chemistry and Chemical TechnologiesUniversity of Calabria87036Arcavacata di Rende (CS)Italy
| | - Alessandro Bonetto
- Dept. Environmental Sciences, Informatics and StatisticsUniversity Ca' Foscari Venice VegaparkVia delle Industrie 21/830175Marghera, VeniceItaly
| | - Antonio Marcomini
- Dept. Environmental Sciences, Informatics and StatisticsUniversity Ca' Foscari Venice VegaparkVia delle Industrie 21/830175Marghera, VeniceItaly
| | - Marcella Bonchio
- Department of Chemical SciencesUniversity of Padovavia Marzolo 135131PadovaItaly
- Consiglio Nazionale delle Ricerche (C.N.R.)Institute on Membrane Technology section of Padovavia Marzolo 135131PadovaItaly
| | - Mirco Natali
- Department of Chemical, Pharmaceutical and Agricultural Sciences (DOCPAS)University of Ferrara, and Centro Interuniversitario per la Conversione Chimica dell'Energia Solare (SOLARCHEM) sez. di Ferraravia L. Borsari 4644121FerraraItaly
| | - Andrea Sartorel
- Department of Chemical SciencesUniversity of Padovavia Marzolo 135131PadovaItaly
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21
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Abstract
The nickel(II) complex [ON(H)O]Ni(PPh3) ([ON(H)O]2- = bis(3,5-di-tert-butyl-2-phenoxy)amine), bearing a protonated redox-active ligand, was examined for its ability to serve as a hydrogen atom (H•) and hydride (H-) donor. Deprotonation of [ON(H)O]Ni(PPh3) afforded the square-planar anion {[ONOcat]Ni(PPh3)}1-, whereas hydrogen atom transfer from [ON(H)O]Ni(PPh3) to TEMPO• in the presence of added PPh3 afforded five-coordinate [ONO]Ni(PPh3)2 that has been structurally characterized. In solution, this five-coordinate complex exists in equilibrium with four-coordinate [ONO]Ni(PPh3), and this ligand exchange equilibrium correlates with a valence tautomerization between the redox-active ligand and the nickel center. Abstraction of a hydride from [ON(H)O]Ni(PPh3) in the presence of PPh3 afforded the octahedral complex, [ONOq]Ni(OTf)(PPh3)2, which was characterized as an S = 1, nickel(II) complex. Bond dissociation free energy (BDFE) and hydricity (ΔG°H-) measurements benchmark the thermodynamic propensity of this complex to participate in ligand-centered H• and H- transfer reactions.
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Affiliation(s)
- Bronte J Charette
- Department of Chemistry, University of California, Irvine, Irvine, California 92677-2025, United States
| | - Joseph W Ziller
- Department of Chemistry, University of California, Irvine, Irvine, California 92677-2025, United States
| | - Alan F Heyduk
- Department of Chemistry, University of California, Irvine, Irvine, California 92677-2025, United States
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22
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Tyburski R, Liu T, Glover SD, Hammarström L. Proton-Coupled Electron Transfer Guidelines, Fair and Square. J Am Chem Soc 2021; 143:560-576. [PMID: 33405896 PMCID: PMC7880575 DOI: 10.1021/jacs.0c09106] [Citation(s) in RCA: 191] [Impact Index Per Article: 63.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Indexed: 12/23/2022]
Abstract
Proton-coupled electron transfer (PCET) reactions are fundamental to energy transformation reactions in natural and artificial systems and are increasingly recognized in areas such as catalysis and synthetic chemistry. The interdependence of proton and electron transfer brings a mechanistic richness of reactivity, including various sequential and concerted mechanisms. Delineating between different PCET mechanisms and understanding why a particular mechanism dominates are crucial for the design and optimization of reactions that use PCET. This Perspective provides practical guidelines for how to discern between sequential and concerted mechanisms based on interpretations of thermodynamic data with temperature-, pressure-, and isotope-dependent kinetics. We present new PCET-zone diagrams that show how a mechanism can switch or even be eliminated by varying the thermodynamic (ΔGPT° and ΔGET°) and coupling strengths for a PCET system. We discuss the appropriateness of asynchronous concerted PCET to rationalize observations in organic reactions, and the distinction between hydrogen atom transfer and other concerted PCET reactions. Contemporary issues and future prospects in PCET research are discussed.
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Affiliation(s)
- Robin Tyburski
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
| | - Tianfei Liu
- Department
of Chemistry, University of North Carolina
at Chapel Hill, Chapel
Hill, North Carolina 27599-3290, United States
| | - Starla D. Glover
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
| | - Leif Hammarström
- Ångström
Laboratory, Department of Chemistry, Uppsala
University, Box 523, SE75120 Uppsala, Sweden
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23
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Zhou Z, Kong X, Liu T. Applications of Proton-Coupled Electron Transfer in Organic Synthesis. CHINESE J ORG CHEM 2021. [DOI: 10.6023/cjoc202106001] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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24
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Walaijai K, Cavill SA, Whitwood AC, Douthwaite RE, Perutz RN. Electrocatalytic Proton Reduction by a Cobalt(III) Hydride Complex with Phosphinopyridine PN Ligands. Inorg Chem 2020; 59:18055-18067. [PMID: 33275426 DOI: 10.1021/acs.inorgchem.0c02505] [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
Cobalt complexes with 2-(diisopropylphosphinomethyl)pyridine (PN) ligands have been synthesized with the aim of demonstrating electrocatalytic proton reduction to dihydrogen with a well-defined hydride complex of an Earth-abundant metal. Reactions of simple cobalt precursors with 2-(diisopropylphosphino-methyl)pyridine (PN) yield [CoII(PN)2(MeCN)][BF4]2 1, [CoIII(PN)2(H)(MeCN)][PF6]2 2, and [CoIII(PN)2(H)(Cl)][PF6] 3. Complexes 1 and 3 have been characterized crystallographically. Unusually for a bidentate PN ligand, all three exhibit geometries with mutually trans phosphorus and nitrogen ligands. Complex 1 exhibits a distorted square-pyramidal geometry with an axial MeCN ligand in a low-spin electronic state. In complexes 2 and 3, the PN ligands lie in a plane leaving the hydride trans to MeCN or chloride, respectively. The redox behavior of the three complexes has been studied by cyclic voltammetry at variable scan rates and by spectroelectrochemistry. A catalytic wave is observed in the presence of trifluoroacetic acid (TFA) at an applied potential close to the Co(II/I) couple of 1. Bulk electrolysis of 1, 2, or 3 at a potential of ca. -1.4 V vs E(Fc+/Fc) in the presence of TFA yields H2 with Faradaic yields close to 100%. A catalytic mechanism is proposed in which the pyridine moiety of a PN ligand acts as a pendant proton donor following opening of the chelate ring. Additional mechanisms may also operate, especially in the presence of high acid concentration where speciation changes.
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Affiliation(s)
- Khanittha Walaijai
- Department of Chemistry, University of York, York YO10 5DD, United Kingdom
| | - Stuart A Cavill
- Department of Physics, University of York, York YO10 5DD, United Kingdom
| | - Adrian C Whitwood
- Department of Chemistry, University of York, York YO10 5DD, United Kingdom
| | | | - Robin N Perutz
- Department of Chemistry, University of York, York YO10 5DD, United Kingdom
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25
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Galvin CM, Waymouth RM. Electron-Rich Phenoxyl Mediators Improve Thermodynamic Performance of Electrocatalytic Alcohol Oxidation with an Iridium Pincer Complex. J Am Chem Soc 2020; 142:19368-19378. [DOI: 10.1021/jacs.0c09605] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Conor M. Galvin
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Robert M. Waymouth
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
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26
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McLoughlin EA, Armstrong KC, Waymouth RM. Electrochemically Regenerable Hydrogen Atom Acceptors: Mediators in Electrocatalytic Alcohol Oxidation Reactions. ACS Catal 2020. [DOI: 10.1021/acscatal.0c03240] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
| | - Keith C. Armstrong
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Robert M. Waymouth
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
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27
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Schreier MR, Pfund B, Guo X, Wenger OS. Photo-triggered hydrogen atom transfer from an iridium hydride complex to unactivated olefins. Chem Sci 2020; 11:8582-8594. [PMID: 34123118 PMCID: PMC8163408 DOI: 10.1039/d0sc01820a] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Accepted: 07/27/2020] [Indexed: 12/18/2022] Open
Abstract
Many photoactive metal complexes can act as electron donors or acceptors upon photoexcitation, but hydrogen atom transfer (HAT) reactivity is rare. We discovered that a typical representative of a widely used class of iridium hydride complexes acts as an H-atom donor to unactivated olefins upon irradiation at 470 nm in the presence of tertiary alkyl amines as sacrificial electron and proton sources. The catalytic hydrogenation of simple olefins served as a test ground to establish this new photo-reactivity of iridium hydrides. Substrates that are very difficult to activate by photoinduced electron transfer were readily hydrogenated, and structure-reactivity relationships established with 12 different olefins are in line with typical HAT reactivity, reflecting the relative stabilities of radical intermediates formed by HAT. Radical clock, H/D isotope labeling, and transient absorption experiments provide further mechanistic insight and corroborate the interpretation of the overall reactivity in terms of photo-triggered hydrogen atom transfer (photo-HAT). The catalytically active species is identified as an Ir(ii) hydride with an IrII-H bond dissociation free energy around 44 kcal mol-1, which is formed after reductive 3MLCT excited-state quenching of the corresponding Ir(iii) hydride, i.e. the actual HAT step occurs on the ground-state potential energy surface. The photo-HAT reactivity presented here represents a conceptually novel approach to photocatalysis with metal complexes, which is fundamentally different from the many prior studies relying on photoinduced electron transfer.
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Affiliation(s)
- Mirjam R Schreier
- Department of Chemistry, University of Basel St. Johanns-Ring 19 4056 Basel Switzerland
| | - Björn Pfund
- Department of Chemistry, University of Basel St. Johanns-Ring 19 4056 Basel Switzerland
| | - Xingwei Guo
- Department of Chemistry, University of Basel St. Johanns-Ring 19 4056 Basel Switzerland
| | - Oliver S Wenger
- Department of Chemistry, University of Basel St. Johanns-Ring 19 4056 Basel Switzerland
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28
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Fernández-Terán R, Ruf J, Hamm P. Vibrational Couplings in Hydridocarbonyl Complexes: A 2D-IR Perspective. Inorg Chem 2020; 59:7721-7726. [DOI: 10.1021/acs.inorgchem.0c00750] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ricardo Fernández-Terán
- Department of Chemistry, University of Zurich. Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Jeannette Ruf
- Department of Chemistry, University of Zurich. Winterthurerstrasse 190, Zurich 8057, Switzerland
| | - Peter Hamm
- Department of Chemistry, University of Zurich. Winterthurerstrasse 190, Zurich 8057, Switzerland
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29
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Swords WB, Meyer GJ, Hammarström L. Excited-state proton-coupled electron transfer within ion pairs. Chem Sci 2020; 11:3460-3473. [PMID: 34109019 PMCID: PMC8152629 DOI: 10.1039/c9sc04941j] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The use of light to drive proton-coupled electron transfer (PCET) reactions has received growing interest, with recent focus on the direct use of excited states in PCET reactions (ES-PCET). Electrostatic ion pairs provide a scaffold to reduce reaction orders and have facilitated many discoveries in electron-transfer chemistry. Their use, however, has not translated to PCET. Herein, we show that ion pairs, formed solely through electrostatic interactions, provide a general, facile means to study an ES-PCET mechanism. These ion pairs formed readily between salicylate anions and tetracationic ruthenium complexes in acetonitrile solution. Upon light excitation, quenching of the ruthenium excited state occurred through ES-PCET oxidation of salicylate within the ion pair. Transient absorption spectroscopy identified the reduced ruthenium complex and oxidized salicylate radical as the primary photoproducts of this reaction. The reduced reaction order due to ion pairing allowed the first-order PCET rate constants to be directly measured through nanosecond photoluminescence spectroscopy. These PCET rate constants saturated at larger driving forces consistent with approaching the Marcus barrierless region. Surprisingly, a proton-transfer tautomer of salicylate, with the proton localized on the carboxylate functional group, was present in acetonitrile. A pre-equilibrium model based on this tautomerization provided non-adiabatic electron-transfer rate constants that were well described by Marcus theory. Electrostatic ion pairs were critical to our ability to investigate this PCET mechanism without the need to covalently link the donor and acceptor or introduce specific hydrogen bonding sites that could compete in alternate PCET pathways.
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Affiliation(s)
- Wesley B Swords
- Department of Chemistry, Ångström Laboratories, Uppsala University Box 523 SE75120 Uppsala Sweden .,Department of Chemistry, University of North Carolina at Chapel Hill Chapel Hill 27599 USA
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill Chapel Hill 27599 USA
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratories, Uppsala University Box 523 SE75120 Uppsala Sweden
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30
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Loewen ND, Berben LA. Secondary Coordination Sphere Design to Modify Transport of Protons and CO2. Inorg Chem 2019; 58:16849-16857. [DOI: 10.1021/acs.inorgchem.9b03102] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Natalia D. Loewen
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Louise A. Berben
- Department of Chemistry, University of California, Davis, California 95616, United States
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31
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Fan J, Cui X, Yu S, Gu L, Zhang Q, Meng F, Peng Z, Ma L, Ma JY, Qi K, Bao Q, Zheng W. Interstitial Hydrogen Atom Modulation to Boost Hydrogen Evolution in Pd-Based Alloy Nanoparticles. ACS NANO 2019; 13:12987-12995. [PMID: 31618006 DOI: 10.1021/acsnano.9b05615] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Rational control of the components of noble metal alloys is paramount for achieving satisfactory electrocatalytic performances. Though transition metals are commonly used to modify noble metals, many potential elements remain to be explored. Here, we interstitially modulate hydrogen atoms into RhPd nanoparticles to boost the alkaline hydrogen evolution reaction (HER). The obtained stable RhPd-H nanoparticles exhibit pronounced alkaline HER activity with a small overpotential of 36.6 mV at 10 mA cm-2 and a low Tafel slope of 35.3 mV dec-1. The surface electronic state, bond distance, and coordination number of the Rh and Pd atoms are significantly influenced by the presence of interstitial hydrogen atoms. These modifications give RhPd-H nanoparticles a desirable hydrogen adsorption free energy, thus accelerating the hydrogen gas production. We further demonstrate that the interstitial hydrogen atom modulation strategy to improve the HER activity is universal for other Pd-based alloy nanostructures. This work presents a powerful strategy for designing efficient electrocatalysts for the HER and beyond.
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Affiliation(s)
- Jinchang Fan
- State Key Laboratory of Automotive Simulation and Control, Department of Materials Science, Key Laboratory of Automobile Materials of MOE , Jilin University , Changchun 130012 , China
| | - Xiaoqiang Cui
- State Key Laboratory of Automotive Simulation and Control, Department of Materials Science, Key Laboratory of Automobile Materials of MOE , Jilin University , Changchun 130012 , China
| | - Shansheng Yu
- State Key Laboratory of Automotive Simulation and Control, Department of Materials Science, Key Laboratory of Automobile Materials of MOE , Jilin University , Changchun 130012 , China
| | - Lin Gu
- Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
| | - Qinghua Zhang
- Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
| | - Fanqi Meng
- Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics , Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
| | - Zhangquan Peng
- State Key Laboratory of Electroanalytical Chemistry , Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun , Jilin 130022 , China
| | - Lipo Ma
- State Key Laboratory of Electroanalytical Chemistry , Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun , Jilin 130022 , China
| | - Jing-Yuan Ma
- Shanghai Synchrotron Radiation Facility , Shanghai Institute of Applied Physics, Chinese Academy of Sciences , Shanghai 201204 , China
| | - Kun Qi
- Department of Materials Science and Engineering and ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET) , Monash University , Clayton , Victoria 3800 , Australia
| | - Qiaoliang Bao
- Department of Materials Science and Engineering and ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET) , Monash University , Clayton , Victoria 3800 , Australia
| | - Weitao Zheng
- State Key Laboratory of Automotive Simulation and Control, Department of Materials Science, Key Laboratory of Automobile Materials of MOE , Jilin University , Changchun 130012 , China
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32
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Liu T, Tyburski R, Wang S, Fernández-Terán R, Ott S, Hammarström L. Elucidating Proton-Coupled Electron Transfer Mechanisms of Metal Hydrides with Free Energy- and Pressure-Dependent Kinetics. J Am Chem Soc 2019; 141:17245-17259. [PMID: 31587555 DOI: 10.1021/jacs.9b08189] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Proton-coupled electron transfer (PCET) was studied in a series of tungsten hydride complexes with pendant pyridyl arms ([(PyCH2Cp)WH(CO)3], PyCH2Cp = pyridylmethylcyclopentadienyl), triggered by laser flash-generated RuIII-tris-bipyridine oxidants, in acetonitrile solution. The free energy dependence of the rate constant and the kinetic isotope effects (KIEs) showed that the PCET mechanism could be switched between concerted and the two stepwise PCET mechanisms (electron-first or proton-first) in a predictable fashion. Straightforward and general guidelines for how the relative rates of the different mechanisms depend on oxidant and base are presented. The rate of the concerted reaction should depend symmetrically on changes in oxidant and base strength, that is on the overall ΔG0PCET, and we argue that an "asynchronous" behavior would not be consistent with a model where the electron and proton tunnel from a common transition state. The observed rate constants and KIEs were examined as a function of hydrostatic pressure (1-2000 bar) and were found to exhibit qualitatively different dependence on pressure for different PCET mechanisms. This is discussed in terms of different volume profiles of the PCET mechanisms as well as enhanced proton tunneling for the concerted mechanism. The results allowed for assignment of the main mechanism operating in the different cases, which is one of the critical questions in PCET research. They also show how the rate of a PCET reaction will be affected very differently by changes of oxidant and base strength, depending on which mechanism dominates. This is of fundamental interest as well as of practical importance for rational design of, for example, catalysts for fuel cells and solar fuel formation, which operate in steps of PCET reactions. The mechanistic richness shown by this system illustrates that the specific mechanism is not intrinsic to a specific synthetic catalyst or enzyme active site but depends on the reaction conditions.
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Affiliation(s)
- Tianfei Liu
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Robin Tyburski
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Shihuai Wang
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Ricardo Fernández-Terán
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Sascha Ott
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
| | - Leif Hammarström
- Department of Chemistry, Ångström Laboratory , Uppsala University , Box 532, SE-751 20 Uppsala , Sweden
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33
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Nazemi A, Cundari TR. Computational Analysis of Proton-Coupled Electron Transfer in Hydrotris(triazolyl)borate Mid–Late 3d and 4d Transition Metal Complexes. Organometallics 2019. [DOI: 10.1021/acs.organomet.9b00322] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Azadeh Nazemi
- Department of Chemistry, Center of Advanced Scientific Computing and Modeling (CASCaM), University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5017, United States
| | - Thomas R. Cundari
- Department of Chemistry, Center of Advanced Scientific Computing and Modeling (CASCaM), University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5017, United States
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34
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Sayfutyarova ER, Lam YC, Hammes-Schiffer S. Strategies for Enhancing the Rate Constant of C-H Bond Cleavage by Concerted Proton-Coupled Electron Transfer. J Am Chem Soc 2019; 141:15183-15189. [PMID: 31464122 DOI: 10.1021/jacs.9b06849] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recently selective C-H bond cleavage under mild conditions with weak oxidants was reported for fluorenyl-benzoates. This mechanism is based on multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an outer-sphere oxidant coupled to intramolecular proton transfer to a well-positioned proton acceptor. The electron transfer driving force depends predominantly on the oxidant, and the proton transfer driving force depends mainly on the basicity of the carboxylate, which is influenced by the substituent on the benzoate fragment. Experiments showed that the rate constants are much more sensitive to the carboxylate basicity than to the redox potential of the oxidant. Herein a vibronically nonadiabatic PCET theory is used to explain how changing the driving force for the electron and proton transfer components of the reaction through varying the oxidant and the substituent, respectively, impacts the PCET rate constant. In addition to increasing the driving force for proton transfer, enhancing the basicity of the carboxylate also decreases the equilibrium proton donor-acceptor distance, thereby facilitating the sampling of shorter proton donor-acceptor distances. This additional effect arising from the strong dependence of proton transfer on the proton donor-acceptor distance provides an explanation for the greater sensitivity of the rate constant to the carboxylate basicity than to the redox potential of the oxidant. These fundamental insights have broad implications for developing new strategies to activate C-H bonds, specifically by designing systems with shorter equilibrium proton donor-acceptor distances.
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Affiliation(s)
- Elvira R Sayfutyarova
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Yan-Choi Lam
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
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35
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Darcy JW, Kolmar SS, Mayer JM. Transition State Asymmetry in C-H Bond Cleavage by Proton-Coupled Electron Transfer. J Am Chem Soc 2019; 141:10777-10787. [PMID: 31199137 DOI: 10.1021/jacs.9b04303] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The selective transformation of C-H bonds is a longstanding challenge in modern chemistry. A recent report details C-H oxidation via multiple-site concerted proton-electron transfer (MS-CPET), where the proton and electron in the C-H bond are transferred to separate sites. Reactivity at a specific C-H bond was achieved by appropriate positioning of an internal benzoate base. Here, we extend that report to reactions of a series of molecules with differently substituted fluorenyl-benzoates and varying outer-sphere oxidants. These results probe the fundamental rate versus driving force relationships in this MS-CPET reaction at carbon by separately modulating the driving force for the proton and electron transfer components. The rate constants depend strongly on the pKa of the internal base, but depend much less on the nature of the outer-sphere oxidant. These observations suggest that the transition states for these reactions are imbalanced. Density functional theory (DFT) was used to generate an internal reaction coordinate, which qualitatively reproduced the experimental observation of a transition state imbalance. Thus, in this system, homolytic C-H bond cleavage involves concerted but asynchronous transfer of the H+ and e-. The nature of this transfer has implications for synthetic methodology and biological systems.
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Affiliation(s)
- Julia W Darcy
- Department of Chemistry , Yale University , New Haven , Connecticut 06520-8107 , United States
| | - Scott S Kolmar
- Department of Chemistry , Yale University , New Haven , Connecticut 06520-8107 , United States
| | - James M Mayer
- Department of Chemistry , Yale University , New Haven , Connecticut 06520-8107 , United States
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36
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Yao C, Dahmen T, Gansäuer A, Norton J. Anti-Markovnikov alcohols via epoxide hydrogenation through cooperative catalysis. Science 2019; 364:764-767. [DOI: 10.1126/science.aaw3913] [Citation(s) in RCA: 93] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Accepted: 04/18/2019] [Indexed: 12/21/2022]
Abstract
The opening of epoxides typically requires electrophilic activation, and subsequent nucleophilic (SN2) attack on the less substituted carbon leads to alcohols with Markovnikov regioselectivity. We describe a cooperative catalysis approach to anti-Markovnikov alcohols by combining titanocene-catalyzed epoxide opening with chromium-catalyzed hydrogen activation and radical reduction. The titanocene enforces the anti-Markovnikov regioselectivity by forming the more highly substituted radical. The chromium catalyst sequentially transfers a hydrogen atom, proton, and electron from molecular hydrogen, avoiding a hydride transfer to the undesired site and resulting in 100% atom economy. Each step of the interconnected catalytic cycles was confirmed separately.
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Affiliation(s)
- Chengbo Yao
- Department of Chemistry, Columbia University, 3000 Broadway, New York, NY 10027, USA
| | - Tobias Dahmen
- Dottikon Exclusive Synthesis AG, Hembrunnstrasse 17, 5605 Dottikon, Switzerland
| | - Andreas Gansäuer
- Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard Domagk Str. 1, 53121 Bonn, Germany
| | - Jack Norton
- Department of Chemistry, Columbia University, 3000 Broadway, New York, NY 10027, USA
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37
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Jackson M, Pegis ML, Surendranath Y. Graphite-Conjugated Acids Reveal a Molecular Framework for Proton-Coupled Electron Transfer at Electrode Surfaces. ACS CENTRAL SCIENCE 2019; 5:831-841. [PMID: 31139719 PMCID: PMC6535968 DOI: 10.1021/acscentsci.9b00114] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Indexed: 05/21/2023]
Abstract
Proton-coupled electron-transfer (PCET) steps play a key role in energy conversion reactions. Molecular PCET reactions are well-described by "square schemes" in which the overall thermochemistry of the reaction is broken into its constituent proton-transfer and electron-transfer components. Although this description has been essential for understanding molecular PCET, no such framework exists for PCET reactions that take place at electrode surfaces. Herein, we develop a molecular square scheme framework for interfacial PCET by investigating the electrochemistry of molecularly well-defined acid/base sites conjugated to graphitic electrodes. Using cyclic voltammetry, we first demonstrate that, irrespective of the redox properties of the corresponding molecular analogue, proton transfer to graphite-conjugated acid/base sites is coupled to electron transfer. We then show that the thermochemistry of surface PCET events can be described by the pK a of the molecular analogue and the potential of zero free charge (zero-field reduction potential) of the electrode. This work provides a general framework for analyzing and predicting the thermochemistry of interfacial PCET reactions.
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38
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Qiu G, Knowles RR. Rate-Driving Force Relationships in the Multisite Proton-Coupled Electron Transfer Activation of Ketones. J Am Chem Soc 2019; 141:2721-2730. [PMID: 30665301 DOI: 10.1021/jacs.8b13451] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Here we present a detailed kinetic study of the multisite proton-coupled electron transfer (MS-PCET) activations of aryl ketones using a variety of Brønsted acids and excited-state Ir(III)-based electron donors. A simple method is described for simultaneously extracting both the hydrogen-bonding equilibrium constants and the rate constants for the PCET event from deconvolution of the luminescence quenching data. These experiments confirm that these activations occur in a concerted fashion, wherein the proton and electron are transferred to the ketone substrate in a single elementary step. The rates constants for the PCET events were linearly correlated with their driving forces over a range of nearly 19 kcal/mol. However, the slope of the rate-driving force relationship deviated significantly from expectations based on Marcus theory. A rationalization for this observation is proposed based on the principle of non-perfect synchronization, wherein factors that serve to stabilize the product are only partially realized at the transition state. A discussion of the relevance of these findings to the applications of MS-PCET in organic synthesis is also presented.
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Affiliation(s)
- Guanqi Qiu
- Department of Chemistry , Princeton University , Princeton , New Jersey 08544 , United States
| | - Robert R Knowles
- Department of Chemistry , Princeton University , Princeton , New Jersey 08544 , United States
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39
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Chu X, Jin J, Ming B, Pang M, Yu X, Tung CH, Wang W. Bimetallic nickel-cobalt hydrides in H 2 activation and catalytic proton reduction. Chem Sci 2019; 10:761-767. [PMID: 30746109 PMCID: PMC6340403 DOI: 10.1039/c8sc04346a] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Accepted: 10/26/2018] [Indexed: 12/18/2022] Open
Abstract
The synergism of the electronic properties of nickel and cobalt enables bimetallic NiCo complexes to process H2. The nickel-cobalt hydride [(dppe)Ni(pdt)(H)CoCp*]+ ([1H]+ ) arising from protonation of the reduced state 1 was found to be an efficient electrocatalyst for H2 evolution with Cl2CHCOOH, and the oxidized [Ni(ii)Co(iii)]2+ form is capable of activating H2 to produce [1H]+ . The features of stereodynamics, acid-base properties, redox chemistry and reactivity of these bimetallic NiCo complexes in processing H2 are potentially related to the active site of [NiFe]-H2ases.
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Affiliation(s)
- Xiaoxiao Chu
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
- School of Chemistry and Materials Science , Ludong University , Yantai , 264025 , China
| | - Jihao Jin
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
| | - Bangrong Ming
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
| | - Maofu Pang
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
| | - Xin Yu
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
| | - Chen-Ho Tung
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
| | - Wenguang Wang
- Key Lab for Colloid and Interface Chemistry of Education Ministry , School of Chemistry and Chemical Engineering , Shandong University , 250100 , China .
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40
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Thammavongsy Z, Mercer IP, Yang JY. Promoting proton coupled electron transfer in redox catalysts through molecular design. Chem Commun (Camb) 2019; 55:10342-10358. [DOI: 10.1039/c9cc05139b] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mini-review on using the secondary coordination sphere to facilitate multi-electron, multi-proton catalysis.
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Affiliation(s)
| | - Ian P. Mercer
- Department of Chemistry
- University of California
- Irvine
- USA
| | - Jenny Y. Yang
- Department of Chemistry
- University of California
- Irvine
- USA
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41
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Pannwitz A, Wenger OS. Proton-coupled multi-electron transfer and its relevance for artificial photosynthesis and photoredox catalysis. Chem Commun (Camb) 2019; 55:4004-4014. [DOI: 10.1039/c9cc00821g] [Citation(s) in RCA: 65] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Photoinduced PCET meets catalysis, and the accumulation of multiple redox equivalents is of key importance.
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Affiliation(s)
- Andrea Pannwitz
- Department of Chemistry
- University of Basel
- 4056 Basel
- Switzerland
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42
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Sayfutyarova ER, Goldsmith ZK, Hammes-Schiffer S. Theoretical Study of C-H Bond Cleavage via Concerted Proton-Coupled Electron Transfer in Fluorenyl-Benzoates. J Am Chem Soc 2018; 140:15641-15645. [PMID: 30383371 DOI: 10.1021/jacs.8b10461] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Developing new strategies to activate and cleave C-H bonds is important for a broad range of applications. Recently a new approach for C-H bond activation using multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an oxidant coupled to intramolecular proton transfer was reported. For a series of oxidants reacting with 2-(9 H-fluoren-9-yl)benzoate, experimental studies revealed an atypical Brønsted α, defined as the slope of the logarithm of the PCET rate constant versus the logarithm of the equilibrium constant or the scaled driving force. Herein this reaction is modeled with a vibronically nonadiabatic PCET theory. Hydrogen tunneling, thermal sampling of the proton donor-acceptor mode, solute and solvent reorganization, and contributions from excited vibronic states are found to play important roles. The calculations qualitatively reproduce the experimental observation of a Brønsted α significantly less than 0.5 and explain this shallow slope in terms of exoergic processes between pairs of electron-proton vibronic states. These fundamental mechanistic insights may guide the design of more effective strategies for C-H bond activation and cleavage.
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Affiliation(s)
- Elvira R Sayfutyarova
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Zachary K Goldsmith
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
| | - Sharon Hammes-Schiffer
- Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States
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Huang T, Rountree ES, Traywick AP, Bayoumi M, Dempsey JL. Switching between Stepwise and Concerted Proton-Coupled Electron Transfer Pathways in Tungsten Hydride Activation. J Am Chem Soc 2018; 140:14655-14669. [PMID: 30362720 DOI: 10.1021/jacs.8b07102] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Catalytic processes to generate (or oxidize) fuels such as hydrogen are underpinned by multiple proton-coupled electron transfer (PCET) steps that are associated with the formation or activation of metal-hydride bonds. Fully understanding the detailed PCET mechanisms of metal hydride transformations holds promise for the rational design of energy-efficient catalysis. Here we investigate the detailed PCET mechanisms for the activation of the transition metal hydride complex CpW(CO)2(PMe3)H (Cp = cyclopentadienyl) using stopped-flow rapid mixing coupled with time-resolved optical spectroscopy. We reveal that all three limiting PCET pathways can be accessed by changing the free energy for elementary proton, electron, and proton-electron transfers through the choice of base and oxidant, with the concerted pathway occurring exclusively as a secondary parallel route. Through detailed kinetics analysis, we define free energy relationships for the kinetics of elementary reaction steps, which provide insight into the factors influencing reaction mechanism. Rate constants for proton transfer processes in the limiting stepwise pathways reveal a large reorganization energy associated with protonation/deprotonation of the metal center (λ = 1.59 eV) and suggest that sluggish proton transfer kinetics hinder access to a concerted route. Rate constants for concerted PCET indicate that the concerted routes are asynchronous. Additionally, through quantification of the relative contributions of parallel stepwise and concerted mechanisms toward net product formation, the influence of various reaction parameters on reactivity are identified. This work underscores the importance of understanding the PCET mechanism for controlling metal hydride reactivity, which could lead to superior catalyst design for fuel production and oxidation.
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Affiliation(s)
- Tao Huang
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Eric S Rountree
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Andrew P Traywick
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Magd Bayoumi
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
| | - Jillian L Dempsey
- Department of Chemistry , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599-3290 , United States
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Darcy JW, Koronkiewicz B, Parada GA, Mayer JM. A Continuum of Proton-Coupled Electron Transfer Reactivity. Acc Chem Res 2018; 51:2391-2399. [PMID: 30234963 DOI: 10.1021/acs.accounts.8b00319] [Citation(s) in RCA: 162] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Proton-coupled electron transfer (PCET) covers a wide range of reactions involving the transfer(s) of electrons and protons. The best-known PCET reaction, hydrogen atom transfer (HAT), has been studied in detail for more than a century. HAT is generally described as the concerted transfer of a hydrogen atom (H• ≡ H+ + e-) from one group to another, Y + H-X → Y-H + X, but a strict definition of HAT has been difficult to establish. Distinctions are more challenging when the transfer of "H•" involves e- and H+ that transfer to/from spatially distinct sites or even completely separate reagents (multiple-site concerted proton-electron transfer, MS-CPET). MS-CPET reactivity is increasingly proposed in biological and synthetic contexts, and some reactions typically described as HAT more resemble MS-CPET. Despite that HAT and MS-CPET reactions "look different," we argue here that these reactions lie on a reactivity continuum, and that they are governed by many of the same key parameters. This Account walks the reader across this PCET reactivity continuum, using a series of studies to show the strong similarities of reactions that move protons and electrons in seemingly different ways. To prepare for our stroll, we describe the thermochemical and kinetic frameworks for HAT and MS-CPET. The driving force for a solution HAT reaction is most easily discussed as the difference in the bond dissociation free energies (BDFEs) of the reactants and products. BDFEs can be analyzed as sums of electron and proton transfer steps and can therefore be obtained from p Ka and E° values. Even though MS-CPET reactions do not make and break H-X bonds in the same way as HAT, the same thermochemical description can be used with the introduction of an effective BDFE (BDFEeff). The BDFEeff of a reductant/acid pair is the free energy of that pair to form H•, which can be obtained from p Ka and E° values in an analogous fashion to a standard BDFE. When the PCET thermochemistry is known, HAT and PCET rate constants can be understood and often predicted using linear free energy relationships (the Brønsted catalysis law) and Marcus theory type approaches. After this background, we walk the reader through a continuum of PCET reactivity. Our journey begins with a study of metal-mediated HAT from hydrocarbon substrates to a metal-oxo complex and travels to the MS-CPET end of the reactivity spectrum, involving the transfer of H+ and e- from the hydroxylamine TEMPOH to two completely separate molecules. These examples, and those in between, are all analyzed within the same thermodynamic and kinetic framework. A description of the first examples of MS-CPET with C-H bonds uses the same framework and highlights the importance of hydrogen bonding and preorganization. The examples and analyses show that the reactions along the PCET continuum are more similar than they are different, and that attempts to divide these reactions into subcategories can obscure much of the essential chemistry. We hope that developing the many common features of these reactions will help experts and newcomers alike to explore exciting new territories in PCET reactivity.
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Affiliation(s)
- Julia W. Darcy
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Brian Koronkiewicz
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Giovanny A. Parada
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
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45
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Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions. Nat Chem 2018; 10:881-887. [DOI: 10.1038/s41557-018-0076-x] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 04/27/2018] [Indexed: 12/19/2022]
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46
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Meng K, Medina-Ramos J, Yibeltal-Ashenafi E, Alvarez JC. Interplay of proton and electron transfer to determine concerted behavior in the proton-coupled electron transfer of glutathione oxidation. Phys Chem Chem Phys 2018; 20:17666-17675. [PMID: 29932186 DOI: 10.1039/c8cp01415a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Glutathione (GSH), whose thiol group dictates its redox chemistry, is oxidized to the thiyl radical (GS˙), which rapidly dimerizes to GSSG. Previously, we found that the oxidation rate of GSH by IrCl62- depends on the base (B) concentration and the pKa of its conjugate acid BH+, so that collateral to a stepwise mechanism, the concerted pathway GSH + IrCl62- + B = GS˙ + IrCl63- + BH+ was proposed as the rate determining step. Herein, this investigation is extended to include oxidant-base pairs that render exothermic and endothermic conditions of ΔG°' for electron transfer (ET) and proton transfer (PT). Experiments were conducted by the reaction of GSH with an electrogenerated oxidant M+ and using digital simulations to infer the mechanism. Data analysis shows that despite parallel mechanisms, the concerted one seems to predominate for the oxidant-base pair that renders the most isoenergetic coupled state, whereby a PT with is capable of producing an ET with , as a result of the Nernstian shift of with pKa. In contrast, the stepwise PT-ET appears to dominate when GS- grows in stability as becomes more negative. Understanding the interplay between ET and PT will help in the design of catalysts for energy harvesting processes that rely on proton-coupled electron transfer.
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Affiliation(s)
- Kejie Meng
- Chemistry Department, Virginia Commonwealth University, Richmond, VA 23284, USA.
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Markle TF, Darcy JW, Mayer JM. A new strategy to efficiently cleave and form C-H bonds using proton-coupled electron transfer. SCIENCE ADVANCES 2018; 4:eaat5776. [PMID: 30027119 PMCID: PMC6044737 DOI: 10.1126/sciadv.aat5776] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 05/31/2018] [Indexed: 05/06/2023]
Abstract
Oxidative activation and reductive formation of C-H bonds are crucial in many chemical, industrial, and biological processes. Reported here is a new strategy for these transformations, using a form of proton-coupled electron transfer (PCET): intermolecular electron transfer coupled to intramolecular proton transfer with an appropriately placed cofactor. In a fluorenyl-benzoate, the positioned carboxylate facilitates rapid cleavage of a benzylic C-H bond upon reaction with even weak 1e- oxidants, for example, decamethylferrocenium. Mechanistic studies establish that the proton and electron transfer to disparate sites in a single concerted kinetic step, via multi-site concerted proton-electron transfer. This work represents a new elementary reaction step available to C-H bonds. This strategy is extended to reductive formation of C-H bonds in two systems. Molecular design considerations and possible utility in synthetic and enzymatic systems are discussed.
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Affiliation(s)
- Todd F. Markle
- Department of Chemistry, Yale University, New Haven, CT 06520–8107, USA
| | - Julia W. Darcy
- Department of Chemistry, Yale University, New Haven, CT 06520–8107, USA
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Taheri A, Carr CR, Berben LA. Electrochemical Methods for Assessing Kinetic Factors in the Reduction of CO2 to Formate: Implications for Improving Electrocatalyst Design. ACS Catal 2018. [DOI: 10.1021/acscatal.8b01799] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Atefeh Taheri
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Cody R. Carr
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Louise A. Berben
- Department of Chemistry, University of California, Davis, California 95616, United States
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Call A, Franco F, Kandoth N, Fernández S, González-Béjar M, Pérez-Prieto J, Luis JM, Lloret-Fillol J. Understanding light-driven H 2 evolution through the electronic tuning of aminopyridine cobalt complexes. Chem Sci 2017; 9:2609-2619. [PMID: 29675253 PMCID: PMC5892349 DOI: 10.1039/c7sc04328g] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Accepted: 12/18/2017] [Indexed: 11/25/2022] Open
Abstract
Electronic effects provide a general mechanistic scenario for rationalizing photocatalytic water reduction activity with aminopyridine cobalt complexes.
A new family of cobalt complexes with the general formula [CoII(OTf)2(Y,XPyMetacn)] (1R, Y,XPyMetacn = 1-[(4-X-3,5-Y-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, (X = CN (1CN), CO2Et (1CO2Et), Cl (1Cl), H (1H), NMe2 (1NMe2)) where (Y = H, and X = OMe when Y = Me (1DMM)) is reported. We found that the electronic tuning of the Y,XPyMetacn ligand not only has an impact on the electronic and structural properties of the metal center, but also allows for a systematic water-reduction-catalytic control. In particular, the increase of the electron-withdrawing character of the pyridine moiety promotes a 20-fold enhancement of the catalytic outcome. By UV-Vis spectroscopy, luminescence quenching studies and Transient Absorption Spectroscopy (TAS), we have studied the direct reaction of the photogenerated [IrIII(ppy)2(bpy˙–)] (PSIr) species to form the elusive CoI intermediates. In particular, our attention is focused on the effect of the ligand architecture in this elemental step of the catalytic mechanism. Finally, kinetic isotopic experiments together with DFT calculations provide complementary information about the rate-determining step of the catalytic cycle.
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Affiliation(s)
- Arnau Call
- Institute of Chemical Research of Catalonia (ICIQ) , The Barcelona Institute of Science and Technology , Avinguda Països Catalans 16 , 43007 Tarragona , Spain .
| | - Federico Franco
- Institute of Chemical Research of Catalonia (ICIQ) , The Barcelona Institute of Science and Technology , Avinguda Països Catalans 16 , 43007 Tarragona , Spain .
| | - Noufal Kandoth
- Institute of Chemical Research of Catalonia (ICIQ) , The Barcelona Institute of Science and Technology , Avinguda Països Catalans 16 , 43007 Tarragona , Spain .
| | - Sergio Fernández
- Institute of Chemical Research of Catalonia (ICIQ) , The Barcelona Institute of Science and Technology , Avinguda Països Catalans 16 , 43007 Tarragona , Spain .
| | - María González-Béjar
- Instituto de Ciencia Molecular (ICMol) , Universidad de Valencia , C/Catedrático José Beltrán 2, Paterna , E46980 Valencia , Spain
| | - Julia Pérez-Prieto
- Instituto de Ciencia Molecular (ICMol) , Universidad de Valencia , C/Catedrático José Beltrán 2, Paterna , E46980 Valencia , Spain
| | - Josep M Luis
- Institut de Química Computacional i Catàlisi (IQCC) , Departament de Química , Universitat de Girona , Campus Montilivi , E17071 Girona , Catalonia , Spain
| | - Julio Lloret-Fillol
- Institute of Chemical Research of Catalonia (ICIQ) , The Barcelona Institute of Science and Technology , Avinguda Països Catalans 16 , 43007 Tarragona , Spain . .,Catalan Institution for Research and Advanced Studies (ICREA) , Passeig Lluïs Companys, 23 , 08010 , Barcelona , Spain
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50
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Smith PJ, Goeltz JC. Proton-Coupled Electron Transfer and Substituent Effects in Catechol-Based Deep Eutectic Solvents: Gross and Fine Tuning of Redox Activity. J Phys Chem B 2017; 121:10974-10978. [DOI: 10.1021/acs.jpcb.7b10169] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Parker J. Smith
- School of Natural Sciences, California State University, Monterey Bay, 100 Campus Center, Seaside, California 93955, United States
| | - John C. Goeltz
- School of Natural Sciences, California State University, Monterey Bay, 100 Campus Center, Seaside, California 93955, United States
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