1
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Ostojić BD, Stanković B, Đorđević DS, Schwerdtfeger P. Reduction of CO 2 in the presence of light via excited-state hydride transfer reaction in a NADPH-inspired derivative. Phys Chem Chem Phys 2024; 26:17504-17520. [PMID: 38416048 DOI: 10.1039/d3cp05635j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/29/2024]
Abstract
The photo-catalytic reduction of CO2 into chemical feedstocks using solar energy has attracted vast interest in environmental science because of global warming. Based on our previous study on the CO2 complex with one of the benzimidazoline (BI) derivatives, we explore the photochemical reduction of CO2 in one of the benzimidazoline derivatives (1,3-dimethyl-5,6-diol-2,3-dihydro-1H-benzimidazole) by quantum-chemical methods. Our results reveal that carbon dioxide can be reduced to formate (HCOO-) by a hydride transfer reaction in the excited state of this complex of benzimidazoline derivative and CO2. While the ground-state hydride transfer reaction in this complex exhibits a substantial barrier, a charge-transfer can occur in the first singlet excited state of the complex in the UV-A region (326 nm), and after overcoming a moderate barrier (∼0.4 eV) the system can have access to the products. The interaction with a polar solvent decreases further the barrier such that the reaction in dimethyl sulfoxide can proceed with a negligibly small barrier (∼0.1 eV) or in a nearly barrierless manner. Our results show that this benzimidazoline derivative may act as a catalyst in the photoreduction of CO2.
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Affiliation(s)
- Bojana D Ostojić
- Center of Excellence in Environmental Chemistry and Engineering, Institute for Chemistry, Technology and Metallurgy, University of Belgrade, Njegoševa 12, Belgrade 11000, Serbia.
| | - Branislav Stanković
- Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia
| | - Dragana S Đorđević
- Center of Excellence in Environmental Chemistry and Engineering, Institute for Chemistry, Technology and Metallurgy, University of Belgrade, Njegoševa 12, Belgrade 11000, Serbia.
| | - Peter Schwerdtfeger
- Centre for Theoretical Chemistry and Physics (CTCP), The New Zealand Institute for Advanced Study (NZIAS), Massey University, Auckland Campus, Private Bag 102904, North Shore City, 0745 Auckland, New Zealand.
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2
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Chirila A, Hu Y, Linehan JC, Dixon DA, Wiedner ES. Thermodynamic and Kinetic Activity Descriptors for the Catalytic Hydrogenation of Ketones. J Am Chem Soc 2024; 146:6866-6879. [PMID: 38437011 DOI: 10.1021/jacs.3c13876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2024]
Abstract
Activity descriptors are a powerful tool for the design of catalysts that can efficiently utilize H2 with minimal energy losses. In this study, we develop the use of hydricity and H- self-exchange rates as thermodynamic and kinetic descriptors for the hydrogenation of ketones by molecular catalysts. Two complexes with known hydricity, HRh(dmpe)2 and HCo(dmpe)2, were investigated for the catalytic hydrogenation of ketones under mild conditions (1.5 atm and 25 °C). The rhodium catalyst proved to be an efficient catalyst for a wide range of ketones, whereas the cobalt catalyst could only hydrogenate electron-deficient ketones. Using a combination of experiment and electronic structure theory, thermodynamic hydricity values were established for 46 alkoxide/ketone pairs in both acetonitrile and tetrahydrofuran solvents. Through comparison of the hydricities of the catalysts and substrates, it was determined that catalysis was observed only for catalyst/ketone pairs with an exergonic H- transfer step. Mechanistic studies revealed that H- transfer was the rate-limiting step for catalysis, allowing for the experimental and computation construction of linear free-energy relationships (LFERs) for H- transfer. Further analysis revealed that the LFERs could be reproduced using Marcus theory, in which the H- self-exchange rates for the HRh/Rh+ and ketone/alkoxide pairs were used to predict the experimentally measured catalytic barriers within 2 kcal mol-1. These studies significantly expand the scope of catalytic reactions that can be analyzed with a thermodynamic hydricity descriptor and firmly establish Marcus theory as a valid approach to develop kinetic descriptors for designing catalysts for H- transfer reactions.
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Affiliation(s)
- Andrei Chirila
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Yiqin Hu
- Department of Chemistry and Biochemistry, University of Alabama, Tuscaloosa, Alabama 35487, United States
| | - John C Linehan
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - David A Dixon
- Department of Chemistry and Biochemistry, University of Alabama, Tuscaloosa, Alabama 35487, United States
| | - Eric S Wiedner
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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3
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Khezeli F, Plaisance C. Computational Design of an Electro-Organocatalyst for Conversion of CO 2 into Formaldehyde. J Phys Chem A 2024; 128:1576-1592. [PMID: 38412517 PMCID: PMC10926098 DOI: 10.1021/acs.jpca.3c07806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Revised: 02/02/2024] [Accepted: 02/05/2024] [Indexed: 02/29/2024]
Abstract
Density functional theory calculations employing a hybrid implicit/explicit solvation method were used to explore a new strategy for electrochemical conversion of CO2 using an electro-organocatalyst. A particular structural motif is identified that consists of an electron-rich vicinal enediamine (>N-C═C-N<) backbone, which is capable of activating CO2 by the formation of a C-C bond while subsequently facilitating the transfer of electrons from a chemically inert cathode to ultimately produce formaldehyde. Unlike transition metal-based electrocatalysts, the electro-organocatalyst is not constrained by scaling relations between the formation energies of activated CO2 and adsorbed CO, nor is it expected to be active for the competing hydrogen evolution reaction. The rate-limiting steps are found to occur during two proton-coupled electron transfer (PCET) sequences and are associated with the transfer of a proton from a proton transfer mediator to a carbon atom on the electro-organocatalyst. The difficulty of this step in the second PCET sequence necessitates an electrode potential of -0.85 V vs RHE to achieve the maximum turnover frequency. In addition, it is postulated that the electro-organocatalyst should also be capable of forming long-chain aldehydes by successively carrying out reductive aldol condensation to grow the alkyl chain one carbon at a time.
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Affiliation(s)
- Foroogh Khezeli
- Cain Department
of Chemical
Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Craig Plaisance
- Cain Department
of Chemical
Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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4
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Torres-Méndez C, Axelsson M, Tian H. Small Organic Molecular Electrocatalysts for Fuels Production. Angew Chem Int Ed Engl 2024; 63:e202312879. [PMID: 37905977 DOI: 10.1002/anie.202312879] [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: 09/05/2023] [Revised: 10/30/2023] [Accepted: 10/31/2023] [Indexed: 11/02/2023]
Abstract
In recent years, heterocyclic organic compounds have been explored as molecular electrocatalysts in relevant reactions for energy conversion and storage. Merging mimetics of biological systems that perform hydride transfer with rational synthetic chemical design has opened many opportunities for organic molecules to be tuned at the atomic level conferring them interesting reactivities. These molecular electrocatalysts represent an alternative to traditional metallic materials and metal complexes employed for water oxidation, hydrogen production, and carbon dioxide reduction. This minireview describes recent reports concerning design, catalytic activity and the mechanism of synthetic molecular electrocatalysts towards solar fuels production.
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Affiliation(s)
- Carlos Torres-Méndez
- Department of Chemistry-Ångström Laboratory, Uppsala University, SE-75120, Uppsala, Sweden
| | - Martin Axelsson
- Department of Chemistry-Ångström Laboratory, Uppsala University, SE-75120, Uppsala, Sweden
| | - Haining Tian
- Department of Chemistry-Ångström Laboratory, Uppsala University, SE-75120, Uppsala, Sweden
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5
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Askins EJ, Zoric MR, Li M, Amine R, Amine K, Curtiss LA, Glusac KD. Triarylmethyl cation redox mediators enhance Li-O 2 battery discharge capacities. Nat Chem 2023; 15:1247-1254. [PMID: 37414882 DOI: 10.1038/s41557-023-01268-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2022] [Accepted: 06/06/2023] [Indexed: 07/08/2023]
Abstract
A major impediment to Li-O2 battery commercialization is the low discharge capacities resulting from electronically insulating Li2O2 film growth on carbon electrodes. Redox mediation offers an effective strategy to drive oxygen chemistry into solution, avoiding surface-mediated Li2O2 film growth and extending discharge lifetimes. As such, the exploration of diverse redox mediator classes can aid the development of molecular design criteria. Here we report a class of triarylmethyl cations that are effective at enhancing discharge capacities up to 35-fold. Surprisingly, we observe that redox mediators with more positive reduction potentials lead to larger discharge capacities because of their improved ability to suppress the surface-mediated reduction pathway. This result provides important structure-property relationships for future improvements in redox-mediated O2/Li2O2 discharge capacities. Furthermore, we applied a chronopotentiometry model to investigate the zones of redox mediator standard reduction potentials and the concentrations needed to achieve efficient redox mediation at a given current density. We expect this analysis to guide future redox mediator exploration.
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Affiliation(s)
- Erik J Askins
- Department of Chemistry, University of Illinois Chicago, Chicago, IL, USA
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA
| | - Marija R Zoric
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Matthew Li
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA
| | - Rachid Amine
- Material Science Division, Argonne National Laboratory, Lemont, IL, USA
| | - Khalil Amine
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA
| | - Larry A Curtiss
- Material Science Division, Argonne National Laboratory, Lemont, IL, USA
| | - Ksenija D Glusac
- Department of Chemistry, University of Illinois Chicago, Chicago, IL, USA.
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA.
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6
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Xie W, Xu J, Md Idros U, Katsuhira J, Fuki M, Hayashi M, Yamanaka M, Kobori Y, Matsubara R. Metal-free reduction of CO 2 to formate using a photochemical organohydride-catalyst recycling strategy. Nat Chem 2023:10.1038/s41557-023-01157-6. [PMID: 36959509 DOI: 10.1038/s41557-023-01157-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Accepted: 02/09/2023] [Indexed: 03/25/2023]
Abstract
Increasing levels of CO2 in the atmosphere is a problem that must be urgently resolved if the rise in current global temperatures is to be slowed. Chemically reducing CO2 into compounds that are useful as energy sources and carbon-based materials could be helpful in this regard. However, for the CO2 reduction reaction (CO2RR) to be operational on a global scale, the catalyst system must: use only renewable energy, be built from abundantly available elements and not require high-energy reactants. Although light is an attractive renewable energy source, most existing CO2RR methods use electricity and many of the catalysts used are based on rare heavy metals. Here we present a transition-metal-free catalyst system that uses an organohydride catalyst based on benzimidazoline for the CO2RR that can be regenerated using a carbazole photosensitizer and visible light. The system is capable of producing formate with a turnover number exceeding 8,000 and generates no other reduced products (such as H2 and CO).
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Affiliation(s)
- Weibin Xie
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
| | - Jiasheng Xu
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
| | - Ubaidah Md Idros
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
| | - Jouji Katsuhira
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
| | - Masaaki Fuki
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
- Molecular Photoscience Research Center, Kobe University, Kobe, Japan
| | - Masahiko Hayashi
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
| | - Masahiro Yamanaka
- Department of Chemistry and Research Center for Smart Molecules, Rikkyo University, Tokyo, Japan.
| | - Yasuhiro Kobori
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan.
- Molecular Photoscience Research Center, Kobe University, Kobe, Japan.
| | - Ryosuke Matsubara
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan.
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7
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Karak P, Mandal SK, Choudhury J. Bis-Imidazolium-Embedded Heterohelicene: A Regenerable NADP + Cofactor Analogue for Electrocatalytic CO 2 Reduction. J Am Chem Soc 2023; 145:7230-7241. [PMID: 36944228 DOI: 10.1021/jacs.2c12883] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/23/2023]
Abstract
Biomimetic NAD(P)H-type organic hydride donors have recently been advocated as potential candidates to act as metal-free catalysts for fuel-forming reactions such as the reduction of CO2 to formic acid and methanol, similar to the natural photosynthesis process of fixing CO2 into carbohydrates. Although these artificial synthetic organic hydrides are extensively used in organic reduction chemistry in a stoichiometric manner, translating them into catalysts has been challenging due to problems associated with the regeneration of these hydride species under applied reaction conditions. A recent discovery of the possibility of their regeneration under electrochemical conditions via a proton-coupled electron-transfer pathway triggered intense research to accomplish their catalytic use in electrochemical CO2 reduction reactions (eCO2RR). However, success is yet to be realized to term them as "true" catalysts, as the typical turnover numbers (TONs) of the eCO2RR processes on inert electrodes for the production of formic acid and/or methanol reported so far are still in the order of 10-3-10-2; thus, sub-stoichiometric only! Herein, we report a novel class of structurally engineered heterohelicene-based organic hydride donor with a proof-of-principle demonstration of catalytic electrochemical CO2 reduction reaction showing a significantly improved activity with more than stoichiometric turnover featuring a 100-1000-fold enhancement of the existing TON values. Mechanistic investigations suggested the critical role of the two cationic imidazolium motifs along with the extensive π-conjugation present in the backbone of the heterohelicene molecules in accessing and stabilizing various radical species involved in the generation and transfer of hydride, via multielectron-transfer steps in the electrochemical process.
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Affiliation(s)
- Pirudhan Karak
- Organometallics & Smart Materials Laboratory, Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal 462 066, India
| | - Sanajit Kumar Mandal
- Organometallics & Smart Materials Laboratory, Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal 462 066, India
| | - Joyanta Choudhury
- Organometallics & Smart Materials Laboratory, Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal 462 066, India
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8
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Fu Y, Yang L, Zhou Z, Jia T, Shen G, Zhu X. Comparison of Thermodynamic Energies for Elementary Steps of Anionic Hydrides to Release Hydride Ions in Acetonitrile. ChemistrySelect 2022. [DOI: 10.1002/slct.202203626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Yan‐Hua Fu
- College of Chemistry and Environmental Engineering Anyang Institute of Technology Anyang Henan 455000 China
| | - Li‐Guo Yang
- College of Chemistry and Environmental Engineering Anyang Institute of Technology Anyang Henan 455000 China
| | - Zhong‐Yuan Zhou
- College of Chemistry and Environmental Engineering Anyang Institute of Technology Anyang Henan 455000 China
| | - Taixuan Jia
- College of Chemistry and Environmental Engineering Anyang Institute of Technology Anyang Henan 455000 China
| | - Guang‐Bin Shen
- School of Medical Engineering Jining Medical University Jining Shandong 272000 P. R. China
| | - Xiao‐Qing Zhu
- Department of Chemistry Nankai University Tianjin 300071 China
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9
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Zhang YQ, Wang ZH, Li M, Liao RZ. Understanding the chemoselectivity switch in CO2 reduction catalyzed by Co and Fe complexes bearing a pentadentate N5 ligand. J Catal 2022. [DOI: 10.1016/j.jcat.2022.09.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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10
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Espinosa MR, Ertem MZ, Barakat M, Bruch QJ, Deziel AP, Elsby MR, Hasanayn F, Hazari N, Miller AJM, Pecoraro MV, Smith AM, Smith NE. Correlating Thermodynamic and Kinetic Hydricities of Rhenium Hydrides. J Am Chem Soc 2022; 144:17939-17954. [PMID: 36130605 DOI: 10.1021/jacs.2c07192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The kinetics of hydride transfer from Re(Rbpy)(CO)3H (bpy = 4,4'-R-2,2'-bipyridine; R = OMe, tBu, Me, H, Br, COOMe, CF3) to CO2 and seven different cationic N-heterocycles were determined. Additionally, the thermodynamic hydricities of complexes of the type Re(Rbpy)(CO)3H were established primarily using computational methods. Linear free-energy relationships (LFERs) derived by correlating thermodynamic and kinetic hydricities indicate that, in general, the rate of hydride transfer increases as the thermodynamic driving force for the reaction increases. Kinetic isotope effects range from inverse for hydride transfer reactions with a small driving force to normal for reactions with a large driving force. Hammett analysis indicates that hydride transfer reactions with greater thermodynamic driving force are less sensitive to changes in the electronic properties of the metal hydride, presumably because there is less buildup of charge in the increasingly early transition state. Bronsted α values were obtained for a range of hydride transfer reactions and along with DFT calculations suggest the reactions are concerted, which enables the use of Marcus theory to analyze hydride transfer reactions involving transition metal hydrides. It is notable, however, that even slight perturbations in the steric properties of the Re hydride or the hydride acceptor result in large deviations in the predicted rate of hydride transfer based on thermodynamic driving forces. This indicates that thermodynamic considerations alone cannot be used to predict the rate of hydride transfer, which has implications for catalyst design.
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Affiliation(s)
- Matthew R Espinosa
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Mehmed Z Ertem
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Mariam Barakat
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Quinton J Bruch
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Anthony P Deziel
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Matthew R Elsby
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Faraj Hasanayn
- Department of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Nilay Hazari
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Alexander J M Miller
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Matthew V Pecoraro
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
| | - Allison M Smith
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Nicholas E Smith
- Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520, United States
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11
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Ostojić BD, Stanković B, Đorđević DS, Schwerdtfeger P. Light-driven reduction of CO 2: thermodynamics and kinetics of hydride transfer reactions in benzimidazoline derivatives. Phys Chem Chem Phys 2022; 24:20357-20370. [PMID: 35980288 DOI: 10.1039/d2cp02867k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
CO2 capture, conversion and storage belong to the holy grail of environmental science. We therefore explore an important photochemical hydride transfer reaction of benzimidazoline derivatives with CO2 in a polar solvent (dimethylsulfoxide) by quantum-chemical methods. While the excited electronic state undergoing hydride transfer to formate (HCOO-) shows a higher reaction path barrier compared to the ground state, a charge-transfer can occur in the near-UV region with nearly barrierless access to the products involving a conical intersection between both electronic states. Such radiationless decay through the hydride transfer reaction and formation of HCCO-via excited electronic states in suitable organic compounds opens the way for future photochemical CO2 reduction. We provide a detailed analysis for the chemical CO2 reduction to the formate anion for 15 different benzimidazoline derivatives in terms of thermodynamic hydricities (ΔGH-), activation free energies (ΔG‡HT), and reaction free energies (ΔGrxn) for the chosen solvent dimethylsulfoxide at the level of density functional theory. The calculated hydricities are in the range from 35.0 to 42.0 kcal mol-1i.e. the species possess strong hydride donor abilities required for the CO2 reduction to formate, characterized by relatively low activation free energies between 18.5 and 22.2 kcal mol-1. The regeneration of the benzimidazoline can be achieved electrochemically.
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Affiliation(s)
- Bojana D Ostojić
- Center of Excellence in Environmental Chemistry and Engineering, Institute for Chemistry, Technology and Metallurgy, University of Belgrade, Njegoševa 12, Belgrade 11000, Serbia.
| | - Branislav Stanković
- Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia
| | - Dragana S Đorđević
- Center of Excellence in Environmental Chemistry and Engineering, Institute for Chemistry, Technology and Metallurgy, University of Belgrade, Njegoševa 12, Belgrade 11000, Serbia.
| | - Peter Schwerdtfeger
- Centre for Theoretical Chemistry and Physics (CTCP), The New Zealand Institute for Advanced Study (NZIAS), Massey University, Auckland Campus, Private Bag 102904, North Shore City, 0745 Auckland, New Zealand
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12
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Ilic S, Gesiorski JL, Weerasooriya RB, Glusac KD. Biomimetic Metal-Free Hydride Donor Catalysts for CO 2 Reduction. Acc Chem Res 2022; 55:844-856. [PMID: 35201767 DOI: 10.1021/acs.accounts.1c00708] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The catalytic reduction of carbon dioxide to fuels and value-added chemicals is of significance for the development of carbon recycling technologies. One of the main challenges associated with catalytic CO2 reduction is product selectivity: the formation of carbon monoxide, molecular hydrogen, formate, methanol, and other products occurs with similar thermodynamic driving forces, making it difficult to selectively reduce CO2 to the target product. Significant scientific effort has been aimed at the development of catalysts that can suppress the undesired hydrogen evolution reaction and direct the reaction toward the selective formation of the desired products, which are easy to handle and store. Inspired by natural photosynthesis, where the CO2 reduction is achieved using NADPH cofactors in the Calvin cycle, we explore biomimetic metal-free hydride donors as catalysts for the selective reduction of CO2 to formate. Here, we outline our recent findings on the thermodynamic and kinetic parameters that control the hydride transfer from metal-free hydrides to CO2. By experimentally measuring and theoretically calculating the thermodynamic hydricities of a range of metal-free hydride donors, we derive structural and electronic factors that affect their hydride-donating abilities. Two dominant factors that contribute to the stronger hydride donors are identified to be (i) the stabilization of the positive charge formed upon HT via aromatization or by the presence of electron-donating groups and (ii) the destabilization of hydride donors through the anomeric effect or in the presence of significant structural constrains in the hydride molecule. Hydride donors with appropriate thermodynamic hydricities were reacted with CO2, and the formation of the formate ion (the first reduction step in CO2 reduction to methanol) was confirmed experimentally, providing an important proof of principle that organocatalytic CO2 reduction is feasible. The kinetics of hydride transfer to CO2 were found to be slow, and the sluggish kinetics were assigned in part to the large self-exchange reorganization energy associated with the organic hydrides in the DMSO solvent. Finally, we outline our approaches to the closure of the catalytic cycle via the electrochemical and photochemical regeneration of the hydride (R-H) from the conjugate hydride acceptors (R+). We illustrate how proton-coupled electron transfer can be efficiently utilized not only to lower the electrochemical potential at which the hydride regeneration takes place but also to suppress the unwanted dimerization that neutral radical intermediates tend to undergo. Overall, this account provides a summary of important milestones achieved in organocatalytic CO2 reduction and provides insights into the future research directions needed for the discovery of inexpensive catalysts for carbon recycling.
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Affiliation(s)
- Stefan Ilic
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, Illinois 60607, United States
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States
| | - Jonathan L. Gesiorski
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, Illinois 60607, United States
| | - Ravindra B. Weerasooriya
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, Illinois 60607, United States
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States
| | - Ksenija D. Glusac
- Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor Street, Chicago, Illinois 60607, United States
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States
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13
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Alkhater MF, Alherz AW, Musgrave CB. Diazaphospholenes as reducing agents: a thermodynamic and electrochemical DFT study. Phys Chem Chem Phys 2021; 23:17794-17802. [PMID: 34382635 DOI: 10.1039/d1cp02193a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Diazaphospholenes have emerged as a promising class of metal-free hydride donors and have been implemented as molecular catalysts in several reduction reactions. Recent studies have also verified their radical reactivity as hydrogen atom donors. Experimental quantification of the hydricities and electrochemical properties of this unique class of hydrides has been limited by their sensitivity towards oxidation in open air and moist environments. Here, we implement quantum chemical density functional theory calculations to analyze the electrochemical catalytic cycle of diazaphospholenes in acetonitrile. We report computed hydricities, reduction potentials, pKa values, and bond dissociation free energies (BDFEs) for 64 P-based hydridic catalysts generated by functionalizing 8 main structures with 8 different electron donating/withdrawing groups. Our results demonstrate that a wide range of hydricities (29-66 kcal mol-1) and BDFEs (58-81 kcal mol-1) are attainable by functionalizing diazaphospholenes. Compared to the more common carbon-based hydrides, diazaphospholenes are predicted to require less negative reduction potentials to electrochemically regenerate hydrides with an equivalent hydridic strength, indicating their higher energy efficiency in the tradeoff between thermodynamic ability and reduction potential. We show that the tradeoff between the reducing ability and the energetic cost of regeneration can be optimized by varying the BDFE and the reorganization energy associated with hydride transfer (λHT), where lower BDFE and λHT correspond to more efficient catalysts. Aromatic phosphorus hydrides with predicted BDFEs of ∼62 kcal mol-1 and λHT's of ∼20 kcal mol-1 are found to require less negative reduction potentials than dihydropyridines and benzimidazoles with predicted BDFEs of ∼68 and ∼84 kcal mol-1 and λHT's of ∼40 and ∼50 kcal mol-1, respectively.
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Affiliation(s)
- Mohammed F Alkhater
- Chemical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
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