1
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Zou M, Kuruppu S, Emge TJ, Waldie KM. Metal- versus ligand-centered reactivity of a cobalt-phenylenediamide complex with electrophiles. Dalton Trans 2024. [PMID: 39045716 DOI: 10.1039/d4dt01655f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2024]
Abstract
A new series of [CoIII-CF3]n+ complexes supported by a bidentate redox-active ligand is presented. The cationic [Co-CF3]+ complex was first obtained by reacting [CpCo(tBuUreaopda)] (Cp = cyclopentadienyl, opda = o-phenylenediamide) with an electrophilic trifluoromethyl source, for which the redox-active phenylenediamide ligand serves as a 2e- reservoir to generate [CpCp(tBuUreabqdi)(CF3)]+ (bqdi = benzoquinonediimine). Electrochemical studies of [Co-CF3]+ revealed two reversible 1e- reductions. Chemical reduction with 1 or 2 equiv. reducing agent enabled isolation of the neutral and anionic complexes, respectively, where the [CoIII-CF3] bond remains intact in all three oxidation states (n = +1, 0, -1). Structural analysis shows systematic changes to the redox-active ligand backbone upon reduction, consistent with sequential ligand-centered electron transfer in the series [bqdi]0 to [s-bqdi]˙- to [opda]2-. In contrast, the reaction of [CpCo(tBuUreaopda)] with alkyl triflates resulted in ligand-centered alkylation at the ureayl groups instead of the targeted Co-alkyl bond formation, suggesting less favorable bond formation at cobalt and greater nucleophilic accessibility of the ligand compared to the metal center.
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Affiliation(s)
- Minzhu Zou
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
| | - Sewwandi Kuruppu
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
| | - Thomas J Emge
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
| | - Kate M Waldie
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
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2
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Luhach S, Lalancette RA, Prokopchuk DE. "Catch and release" of the Cp N3 ligand using cobalt: dissociation, protonation, and C-H bond thermochemistry. Dalton Trans 2024. [PMID: 38916110 DOI: 10.1039/d4dt01560f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/26/2024]
Abstract
The coordination chemistry of an amine-rich CpN3 ligand has been explored with cobalt. We demonstrate that in the presence of NaCo(CO)4, the cationic precursor [CpN3]+ yields the complex CpN3CoI(CO)2. While 2e- oxidation generates new CoIII complexes such as [CpN3Co(NCMe)3]2+ and CpN3CoI2(CO), subsequent ligand loss is facile, generating free [CpN3]+ or the protonated dication [CpN3H]2+. We have structurally characterized both these ligand release products via single crystal X-ray diffraction and obtained thermochemical C-H bond strengths via experiment and density functional theory (DFT). Upon reversible 1e- reduction, the radical cation [CpN3H]˙+ has a weak C-H BDFE of 52 kcal mol-1 in acetonitrile. Mechanistic analysis shows that [CpN3H]˙+ undergoes radical-radical disproportionation in the absence of exogenous H-atom acceptors, which is supported by deuterium isotope labelling experiments. Structural comparison of these organic molecules shows a high degree of iminium-like electron delocalization over the C-N bonds connected to the central five-membered ring.
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Affiliation(s)
- Sanju Luhach
- Department of Chemistry, Rutgers University-Newark, 73 Warren Street, Newark, NJ 07102, USA.
| | - Roger A Lalancette
- Department of Chemistry, Rutgers University-Newark, 73 Warren Street, Newark, NJ 07102, USA.
| | - Demyan E Prokopchuk
- Department of Chemistry, Rutgers University-Newark, 73 Warren Street, Newark, NJ 07102, USA.
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3
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Sporzyński A, Adamczyk-Woźniak A, Zarzeczańska D, Gozdalik JT, Ramotowska P, Abramczyk W. Acidity Constants of Boronic Acids as Simply as Possible: Experimental, Correlations, and Prediction. Molecules 2024; 29:2713. [PMID: 38893585 PMCID: PMC11173951 DOI: 10.3390/molecules29112713] [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: 05/10/2024] [Revised: 05/23/2024] [Accepted: 05/30/2024] [Indexed: 06/21/2024] Open
Abstract
The wide use of boronic compounds, especially boronic acids and benzoxaboroles, in virtually all fields of chemistry is related to their specific properties. The most important of them are the ability to form cyclic esters with diols and the complexation of anions. In both cases, the equilibrium of the reaction depends mainly on the acidity of the compounds, although other factors must also be taken into account. Quantification of the acidity (pKa value) is a fundamental factor considered when designing new compounds of practical importance. The aim of the current work was to collect available values of the acidity constants of monosubstituted phenylboronic acids, critically evaluate these data, and supplement the database with data for missing compounds. Measurements were made using various methods, as a result of which a fast and reliable method for determining the pKa of boronic compounds was selected. For an extensive database of monosubstituted phenylboronic acids, their correlation with their Brønsted analogues-namely carboxylic acids-was examined. Compounds with ortho substituents do not show any correlation, which is due to the different natures of both types of acids. Nonetheless, both meta- and para-substituted compounds show excellent correlation. From a practical point of view, acidity constants are best determined from the Hammett equation. Computational approaches for determining acidity constants were also analyzed. In general, the reported calculated values are not compatible with experimental ones, providing comparable results only for selected groups of compounds.
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Affiliation(s)
- Andrzej Sporzyński
- Faculty of Agriculture and Forestry, University of Warmia and Mazury, Oczapowskiego 2, 10-719 Olsztyn, Poland;
| | - Agnieszka Adamczyk-Woźniak
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland; (A.A.-W.); (J.T.G.)
| | - Dorota Zarzeczańska
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland; (D.Z.); (P.R.)
| | - Jan T. Gozdalik
- Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland; (A.A.-W.); (J.T.G.)
| | - Paulina Ramotowska
- Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland; (D.Z.); (P.R.)
| | - Wiktoria Abramczyk
- Faculty of Agriculture and Forestry, University of Warmia and Mazury, Oczapowskiego 2, 10-719 Olsztyn, Poland;
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4
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Amtawong J, Montgomery CL, Bein GP, Raithel AL, Hamann TW, Chen CH, Dempsey JL. Mechanism-Guided Kinetic Analysis of Electrocatalytic Proton Reduction Mediated by a Cobalt Catalyst Bearing a Pendant Basic Site. J Am Chem Soc 2024; 146:3742-3754. [PMID: 38316637 DOI: 10.1021/jacs.3c10408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
Cobalt polypyridyl complexes stand out as efficient catalysts for electrochemical proton reduction, but investigations into their operating mechanisms, with broad-reaching implications in catalyst design, have been limited. Herein, we investigate the catalytic activity of a cobalt(II) polypyridyl complex bearing a pendant pyridyl base with a series of organic acids spanning 20 pKa units in acetonitrile. Structural analysis, as well as electrochemical studies, reveals that the Co(III) hydride intermediate is formed through reduction of the Co(II) catalyst followed by direct metal protonation in the initial EC step despite the presence of the pendant base, which is commonly thought of as a more kinetically accessible protonation site. Protonation of the pendant base occurs after the Co(III) hydride intermediate is further reduced in the overall ECEC pathway. Additionally, when the acid used is sufficiently strong, the Co(II) catalyst can be protonated, and the Co(III) hydride can react directly with acid to release H2. With thorough mechanistic understanding, the appropriate electroanalytical methods were identified to extract rate constants for the elementary steps over a range of conditions. Thermodynamic square schemes relating catalytic intermediates proposed in the three electrocatalytic HER mechanisms were constructed. These findings reveal a full description of the HER electrocatalysis mediated by this molecular system and provide insights into strategies to improve synthetic fuel-forming catalysts operative through metal hydride intermediates.
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Affiliation(s)
- Jaruwan Amtawong
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Charlotte L Montgomery
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Gabriella P Bein
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Austin L Raithel
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Thomas W Hamann
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States
| | - Chun-Hsing Chen
- 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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5
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Wang T, He F, Jiang W, Liu J. Electrohydrogenation of Nitriles with Amines by Cobalt Catalysis. Angew Chem Int Ed Engl 2024; 63:e202316140. [PMID: 38124405 DOI: 10.1002/anie.202316140] [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: 10/24/2023] [Revised: 12/19/2023] [Accepted: 12/20/2023] [Indexed: 12/23/2023]
Abstract
Catalytic hydrogenation of nitriles represents an efficient and sustainable one-step synthesis of valuable bulk and fine chemicals. We report herein a molecular cobalt electrocatalyst for selective hydrogenative coupling of nitriles with amines using protons as the hydrogen source. The key to success for this reductive reaction is the use of an electrocatalytic approach for efficient cobalt-hydride generation through a sequence of cathodic reduction and protonation. As only electrons (e- ) and protons (H+ ) as the redox equivalent and hydrogen source, this general electrohydrogenation protocol is showcased by highly selective and straightforward synthesis of various functionalized and structurally diverse amines, as well as deuterium isotope labeling applications. Mechanistic studies reveal that the electrogenerated cobalt-hydride transfer to nitrile process is the rate-determining step.
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Affiliation(s)
- Tiantian Wang
- College of Chemistry and Chemical Engineering, State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, 410082, Changsha, China
| | - Fangfang He
- College of Chemistry and Chemical Engineering, State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, 410082, Changsha, China
| | - Wei Jiang
- College of Chemistry and Chemical Engineering, State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, 410082, Changsha, China
| | - Jie Liu
- College of Chemistry and Chemical Engineering, State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, 410082, Changsha, China
- Greater Bay Area Institute for Innovation, Hunan University, 511300, Guangzhou, Guangdong Province, China
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6
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Kumar P, Tyagi VP, Ghosh M. Exploring the Multifarious Role of the Ligand in Electrocatalytic Hydrogen Evolution Reaction Pathways. Chemistry 2023; 29:e202302195. [PMID: 37728113 DOI: 10.1002/chem.202302195] [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: 07/10/2023] [Revised: 09/18/2023] [Accepted: 09/18/2023] [Indexed: 09/21/2023]
Abstract
In recent years, researchers have shifted their focus towards investigating the redox properties of ancillary ligand backbones for small-molecule activation. Several metal complexes have been reported for the electrocatalytic H2 evolution reaction (HER), providing valuable mechanistic insights. This process involves efficient coupling of electrons and protons. Redox-active ligands stipulate internal electron transfer and promote effective orbital overlap between metal and ligand, thereby, enabling efficient proton-coupled electron transfer reactions. Understanding such catalytic mechanisms requires thorough spectroscopic and computational analyses. Herein, we summarize recent examples of molecular electrocatalysts based on 3d transition metals that have significantly influenced mechanistic pathways, thus, emphasizing the multifaceted role of metal-ligand cooperativity.
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Affiliation(s)
- Pankaj Kumar
- Department of Chemistry, Ashoka University, Plot #2, Rajiv Gandhi Education City, National Capital Region, 131029, Sonipat, Haryana, India
| | - Vyom Prakash Tyagi
- Department of Chemistry, Ashoka University, Plot #2, Rajiv Gandhi Education City, National Capital Region, 131029, Sonipat, Haryana, India
| | - Munmun Ghosh
- Department of Chemistry, Ashoka University, Plot #2, Rajiv Gandhi Education City, National Capital Region, 131029, Sonipat, Haryana, India
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7
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Montgomery CL, Amtawong J, Jordan AM, Kurtz DA, Dempsey JL. Proton transfer kinetics of transition metal hydride complexes and implications for fuel-forming reactions. Chem Soc Rev 2023; 52:7137-7169. [PMID: 37750006 DOI: 10.1039/d3cs00355h] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/27/2023]
Abstract
Proton transfer reactions involving transition metal hydride complexes are prevalent in a number of catalytic fuel-forming reactions, where the proton transfer kinetics to or from the metal center can have significant impacts on the efficiency, selectivity, and stability associated with the catalytic cycle. This review correlates the often slow proton transfer rate constants of transition metal hydride complexes to their electronic and structural descriptors and provides perspective on how to exploit these parameters to control proton transfer kinetics to and from the metal center. A toolbox of techniques for experimental determination of proton transfer rate constants is discussed, and case studies where proton transfer rate constant determination informs fuel-forming reactions are highlighted. Opportunities for extending proton transfer kinetic measurements to additional systems are presented, and the importance of synergizing the thermodynamics and kinetics of proton transfer involving transition metal hydride complexes is emphasized.
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Affiliation(s)
- Charlotte L Montgomery
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Jaruwan Amtawong
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Aldo M Jordan
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Daniel A Kurtz
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
| | - Jillian L Dempsey
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
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8
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Boucher DG, Pendergast AD, Wu X, Nguyen ZA, Jadhav RG, Lin S, White HS, Minteer SD. Unraveling Hydrogen Atom Transfer Mechanisms with Voltammetry: Oxidative Formation and Reactivity of Cobalt Hydride. J Am Chem Soc 2023; 145:17665-17677. [PMID: 37530748 DOI: 10.1021/jacs.3c03815] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/03/2023]
Abstract
The utility of transition metal hydride catalyzed hydrogen atom transfer (MHAT) has been widely demonstrated in organic transformations such as alkene isomerization and hydrofunctionalization reactions. However, the highly reactive nature of the hydride and radical intermediates has hindered mechanistic insight into this pivotal reaction. Recent advances in electrochemical MHAT have opened up the possibility for new analytical approaches for mechanistic diagnosis. Here, we report a voltammetric interrogation of Co-based MHAT reactivity, describing in detail the oxidative formation and reactivity of the key Co-H intermediate and its reaction with aryl alkenes. Insights from cyclic voltammetry and finite element simulations help elucidate the rate-limiting step as metal hydride formation, which we show to be widely tunable based on ligand design. Voltammetry is also suggestive of the formation of Co-alkyl intermediates and a dynamic equilibrium with the reactive neutral radical. These mechanistic studies provide information for the design of future hydrofunctionalization reactions, such as catalyst and silane choice, the relative stability of metal-alkyl species, and how hydrofunctionalization reactions utilize Co-alkyl intermediates. In summary, these studies establish an important template for studying MHAT reactions from the perspective of electrochemical kinetic frameworks.
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Affiliation(s)
- Dylan G Boucher
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Andrew D Pendergast
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Xiangyu Wu
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Zachary A Nguyen
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Rohit G Jadhav
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Song Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Henry S White
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Shelley D Minteer
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
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9
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VanderWeide A, Prokopchuk DE. Cyclopentadienyl ring activation in organometallic chemistry and catalysis. Nat Rev Chem 2023:10.1038/s41570-023-00501-1. [PMID: 37258685 DOI: 10.1038/s41570-023-00501-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/25/2023] [Indexed: 06/02/2023]
Abstract
The cyclopentadienyl (Cp) ligand is a cornerstone of modern organometallic chemistry. Since the discovery of ferrocene, the Cp ligand and its various derivatives have become foundational motifs in catalysis, medicine and materials science. Although largely considered an ancillary ligand for altering the stereoelectronic properties of transition metal centres, there is mounting evidence that the core Cp ring structure also serves as a reservoir for reactive protons (H+), hydrides (H-) or radical hydrogen (H•) atoms. This Review chronicles the field of Cp ring activation, highlighting the pivotal role that Cp ligands can have in electrocatalytic H2 production, N2 reduction, hydride transfer reactions and proton-coupled electron transfer.
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10
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Bohn A, Moreno JJ, Thuéry P, Robert M, Rivada-Wheelaghan O. Electrocatalytic CO 2 Reduction with a Binuclear Bis-Terpyridine Pyrazole-Bridged Cobalt Complex. Chemistry 2023; 29:e202202361. [PMID: 36330884 PMCID: PMC10107111 DOI: 10.1002/chem.202202361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 10/30/2022] [Accepted: 11/04/2022] [Indexed: 11/06/2022]
Abstract
A pyrazole-based ligand substituted with terpyridine groups at the 3 and 5 positions has been synthesized to form the dinuclear cobalt complex 1, that electrocatalytically reduces carbon dioxide (CO2 ) to carbon monoxide (CO) in the presence of Brønsted acids in DMF. Chemical, electrochemical and UV-vis spectro-electrochemical studies under inert atmosphere indicate pairwise reduction processes of complex 1. Infrared spectro-electrochemical studies under CO2 and CO atmosphere are consistent with a reduced CO-containing dicobalt complex which results from the electroreduction of CO2 . In the presence of trifluoroethanol (TFE), electrocatalytic studies revealed single-site mechanism with up to 94 % selectivity towards CO formation when 1.47 M TFE were present, at -1.35 V vs. Saturated Calomel Electrode in DMF (0.39 V overpotential). The low faradaic efficiencies obtained (<50 %) are attributed to the generation of CO-containing species formed during the electrocatalytic process, which inhibit the reduction of CO2 .
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Affiliation(s)
- Antoine Bohn
- Laboratoire d'Electrochimie Moléculaire, Université Paris Cité, CNRS, 75006, Paris, France
| | - Juan José Moreno
- Instituto de Investigaciones Químicas (IIQ), Departamento de Química Inorgánica, Consejo Superior de Investigaciones Científicas (CSIC) and Universidad de Sevilla, Avenida Américo Vespucio 49, 41092, Sevilla, Spain
| | - Pierre Thuéry
- NIMBE, Université Paris-Saclay, CEA, CNRS, 91191, Gif-sur-Yvette, France
| | - Marc Robert
- Laboratoire d'Electrochimie Moléculaire, Université Paris Cité, CNRS, 75006, Paris, France.,Institut Universitaire de France (IUF), 75005, Paris, France
| | - Orestes Rivada-Wheelaghan
- Laboratoire d'Electrochimie Moléculaire, Université Paris Cité, CNRS, 75006, Paris, France.,Instituto de Investigaciones Químicas (IIQ), Departamento de Química Inorgánica, Consejo Superior de Investigaciones Científicas (CSIC) and Universidad de Sevilla, Avenida Américo Vespucio 49, 41092, Sevilla, Spain
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11
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Pattanayak S, Berben LA. Pre-Equilibrium Reaction Mechanism as a Strategy to Enhance Rate and Lower Overpotential in Electrocatalysis. J Am Chem Soc 2023; 145:3419-3426. [PMID: 36734988 PMCID: PMC9936576 DOI: 10.1021/jacs.2c10942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Pre-equilibrium reaction kinetics enable the overall rate of a catalytic reaction to be orders of magnitude faster than the rate-determining step. Herein, we demonstrate how pre-equilibrium kinetics can be applied to breaking the linear free-energy relationship (LFER) for electrocatalysis, leading to rate enhancement 5 orders of magnitude and lowering of overpotential to approximately thermoneutral. This approach is applied to pre-equilibrium formation of a metal-hydride intermediate to achieve fast formate formation rates from CO2 reduction without loss of selectivity (i.e., H2 evolution). Fast pre-equilibrium metal-hydride formation, at 108 M-1 s-1, boosts the CO2 electroreduction to formate rate up to 296 s-1. Compared with molecular catalysts that have similar overpotential, this rate is enhanced by 5 orders of magnitude. As an alternative comparison, overpotential is lowered by ∼50 mV compared to catalysts with a similar rate. The principles elucidated here to obtain pre-equilibrium reaction kinetics via catalyst design are general. Design and development that builds on these principles should be possible in both molecular homogeneous and heterogeneous electrocatalysis.
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12
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Thomas-Colwell J, Sookezian A, Kurtz DA, Kallick J, Henling LM, Stich TA, Hill MG, Hunter BM. Tuning Cobalt(II) Phosphine Complexes to be Axially Ambivalent. Inorg Chem 2022; 61:12625-12634. [PMID: 35920800 PMCID: PMC9387527 DOI: 10.1021/acs.inorgchem.2c01562] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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We report the isolation and characterization of a series
of three
cobalt(II) bis(phosphine) complexes with varying numbers of coordinated
solvent ligands in the axial position. X-ray quality crystals of [Co(dppv)2][BF4]2(1), [Co(dppv)2(NCCH3)][BPh4]2(2), and [Co(dppv)2(NCCH3)2][BF4]2(3) (dppv = cis-1,2-bis(diphenylphosphino)ethylene) were grown under slightly different
conditions, and their structures were compared. This analysis revealed
multiple crystallization motifs for divalent cobalt(II) complexes
with the same set of phosphine ligands. Notably, the 4-coordinate
complex 1 is a rare example of a square-planar cobalt(II)
complex, the first crystallographically characterized square-planar
Co(II) complex containing only neutral, bidentate ligands. Characterization
of the different axial geometries via EPR and UV–visible spectroscopies
showed that there is a very shallow energy landscape for axial ligation.
Ligand field angular overlap model calculations support this conclusion,
and we provide a strategy for tuning other ligands to be axially labile
on a phosphine scaffold. This methodology is proposed to be used for
designing cobalt phosphine catalysts for a variety of oxidation and
reduction reactions. A
square-planar cobalt(II) complex featuring two chelating
diphosphine ligands was isolated with 0, 1, and 2 axial acetonitrile
ligands. AOM calculations, validated by EPR, suggest this “axial
ambivalence” results from the near degeneracy of the dx2 − y2/dz2 orbital energies, with a change in the parentage
of the SOMO upon axial ligation. The calculations additionally provide
a simple method of predicting square-planar ligand sets/geometries
tuned to bind axial substrates with varying s-donor strengths.
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Affiliation(s)
- Jack Thomas-Colwell
- Department of Chemistry, Occidental College, Los Angeles, California 90041, United States
| | - Arvin Sookezian
- Department of Chemistry, Occidental College, Los Angeles, California 90041, United States
| | - Daniel A Kurtz
- Rowland Institute at Harvard University, Cambridge, Massachusetts 02142, United States
| | - Jeremy Kallick
- Department of Chemistry, Occidental College, Los Angeles, California 90041, United States
| | - Lawrence M Henling
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Troy A Stich
- Department of Chemistry, Wake Forest University, Winston-Salem, North Carolina 27109, United States
| | - Michael G Hill
- Department of Chemistry, Occidental College, Los Angeles, California 90041, United States
| | - Bryan M Hunter
- Rowland Institute at Harvard University, Cambridge, Massachusetts 02142, United States
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13
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Dey S, Masero F, Brack E, Fontecave M, Mougel V. Electrocatalytic metal hydride generation using CPET mediators. Nature 2022; 607:499-506. [PMID: 35859199 DOI: 10.1038/s41586-022-04874-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 05/16/2022] [Indexed: 11/09/2022]
Abstract
Transition metal hydrides (M-H) are ubiquitous intermediates in a wide range of enzymatic processes and catalytic reactions, playing a central role in H+/H2 interconversion1, the reduction of CO2 to formic acid (HCOOH)2 and in hydrogenation reactions. The facile formation of M-H is a critical challenge to address to further improve the energy efficiency of these reactions. Specifically, the easy electrochemical generation of M-H using mild proton sources is key to enable high selectivity versus competitive CO and H2 formation in the CO2 electroreduction to HCOOH, the highest value-added CO2 reduction product3. Here we introduce a strategy for electrocatalytic M-H generation using concerted proton-electron transfer (CPET) mediators. As a proof of principle, the combination of a series of CPET mediators with the CO2 electroreduction catalyst [MnI(bpy)(CO)3Br] (bpy = 2,2'-bipyridine) was investigated, probing the reversal of the product selectivity from CO to HCOOH to evaluate the efficiency of the manganese hydride (Mn-H) generation step. We demonstrate the formation of the Mn-H species by in situ spectroscopic techniques and determine the thermodynamic boundary conditions for this mechanism to occur. A synthetic iron-sulfur cluster is identified as the best CPET mediator for the system, enabling the preparation of a benchmark catalytic system for HCOOH generation.
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Affiliation(s)
- Subal Dey
- Department of Chemistry and Applied Biosciences, ETH Zürich, Zurich, Switzerland
- Laboratoire de Chimie des Processus Biologiques, UMR 8229 CNRS, Collège de France, Sorbonne Université, Paris, France
| | - Fabio Masero
- Department of Chemistry and Applied Biosciences, ETH Zürich, Zurich, Switzerland
| | - Enzo Brack
- Department of Chemistry and Applied Biosciences, ETH Zürich, Zurich, Switzerland
| | - Marc Fontecave
- Laboratoire de Chimie des Processus Biologiques, UMR 8229 CNRS, Collège de France, Sorbonne Université, Paris, France
| | - Victor Mougel
- Department of Chemistry and Applied Biosciences, ETH Zürich, Zurich, Switzerland.
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14
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Stern CM, Meche DD, Elgrishi N. Impact of the choice of buffer on the electrochemical reduction of Cr( vi) in water on carbon electrodes. RSC Adv 2022; 12:32592-32599. [DOI: 10.1039/d2ra05943f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 11/08/2022] [Indexed: 11/16/2022] Open
Abstract
The nature of the buffer influences the PCET step gating Cr(vi) reduction in water at pH 4.75, as well as the extent of deposition on carbon electrodes. Electrode activity is recovered without polishing, through a simple acid wash step.
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Affiliation(s)
- Callie M. Stern
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA, 70803, USA
| | - Devin D. Meche
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA, 70803, USA
| | - Noémie Elgrishi
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA, 70803, USA
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15
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Sánchez P, Goel B, Neugebauer H, Lalancette RA, Grimme S, Hansen A, Prokopchuk DE. Ligand Protonation at Carbon, not Nitrogen, during H 2 Production with Amine-Rich Iron Electrocatalysts. Inorg Chem 2021; 60:17407-17413. [PMID: 34735115 DOI: 10.1021/acs.inorgchem.1c03142] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
We present monometallic H2 production electrocatalysts containing electron-rich triamine-cyclopentadienyl (Cp) ligands coordinated to iron. After selective CO extrusion from the iron tricarbonyl precursors, electrocatalysis is observed via cyclic voltammetry in the presence of an exogenous acid. Contrary to the fact that amines in the secondary coordination sphere are often protonated during electrocatalysis, comprehensive quantum-chemical calculations indicate that the amines likely do not function as proton relays; instead, endo-Cp ring protonation is most favorable after 1e- reduction. This unusual mechanistic pathway emphasizes the need to consider a broad domain of H+/e- addition products by synergistically combining experimental and theoretical resources.
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Affiliation(s)
- Práxedes Sánchez
- Department of Chemistry, Rutgers University─Newark, 73 Warren Street, Newark, New Jersey 07102, United States
| | - Bhumika Goel
- Department of Chemistry, Rutgers University─Newark, 73 Warren Street, Newark, New Jersey 07102, United States
| | - Hagen Neugebauer
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraße 4, Bonn 53115, Germany
| | - Roger A Lalancette
- Department of Chemistry, Rutgers University─Newark, 73 Warren Street, Newark, New Jersey 07102, United States
| | - Stefan Grimme
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraße 4, Bonn 53115, Germany
| | - Andreas Hansen
- Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms Universität Bonn, Beringstraße 4, Bonn 53115, Germany
| | - Demyan E Prokopchuk
- Department of Chemistry, Rutgers University─Newark, 73 Warren Street, Newark, New Jersey 07102, United States
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16
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Du J, Yang H, Wang CL, Zhan SZ. Synthesis, structure, characterization, EPR investigation and catalytic behavior for hydrogen evolution of a bis(thiosemicarbazonato)-palladium complex. Polyhedron 2021. [DOI: 10.1016/j.poly.2021.115426] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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17
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Zurakowski JA, Austen BJH, Dufour MC, Bhattacharyya M, Spasyuk DM, Drover MW. Preparation of a borane-appended Co(III) hydride: evidence for metal-ligand cooperativity in O-H bond activation. Dalton Trans 2021; 50:12440-12447. [PMID: 34397061 DOI: 10.1039/d1dt02331d] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cobalt hydrides are known to mediate a number of important chemical transformations including proton (H+), hydride (H-), and hydrogen-atom (H˙) transfer. Central to the tunability of such frameworks is judicious ligand design, which offers the flexibility to alter fundamental properties relevant to reactivity. Herein, we report the preparation of one such cobalt(iii) hydride: [Cp*CoIII(P2BCy4)(H)]BPh4 (Cp* = C5Me5-, P2BCy4 = 1,2-bis(di(3-dicyclohexylborane)propylphosphino)ethane) that is encircled by a boron-based Lewis-acidic secondary coordination sphere. The structure of this species is supported by synchrotron-radiation crystallography, evidencing a terminal Co(iii) hydride with four sp2-hybridized boranes that invite Lewis base coordination. To this end, electrochemical reactivity studies performed using [Cp*CoIII(P2BCy4)Cl]+ or an "all-akyl" model, [Cp*CoIII(dnppe)Cl]+ (dnppe = 1,2-bis(di-n-propylphosphino)ethane) with benzoic or 4-pyridylbenzoic acid show divergent responses for protonation of electrochemically-generated Co(i) to give a Co(iii) hydride. For [Cp*CoIII(P2BCy4)Cl]+, this process is complex, not only involving protonation, but also engagement of the pendant borane moieties in Lewis acid/base interactions. For protonation by benzoic acid, for example, borane-benzoate contacts are substantiated by variable temperature NMR spectroscopic measurements and theoretical calculations, pointing to a cooperative Co-H/B-O bond forming process. These data are discussed in the context of designing new molecular catalysts for ligand-assisted hydrogen evolution reactivity.
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Affiliation(s)
- Joseph A Zurakowski
- Department of Chemistry and Biochemistry, The University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
| | - Brady J H Austen
- Department of Chemistry and Biochemistry, The University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
| | - Maeve C Dufour
- Department of Chemistry and Biochemistry, The University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
| | - Moulika Bhattacharyya
- Department of Chemistry and Biochemistry, The University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
| | - Denis M Spasyuk
- Canadian Light Source Inc., 44 Innovation Blvd., Saskatoon, SK S7N 2V3, Canada
| | - Marcus W Drover
- Department of Chemistry and Biochemistry, The University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
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18
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Derosa J, Garrido-Barros P, Peters JC. Electrocatalytic Reduction of C-C π-Bonds via a Cobaltocene-Derived Concerted Proton-Electron Transfer Mediator: Fumarate Hydrogenation as a Model Study. J Am Chem Soc 2021; 143:9303-9307. [PMID: 34138550 DOI: 10.1021/jacs.1c03335] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Reductive concerted proton-electron transfer (CPET) is poorly developed for the reduction of C-C π-bonds, including for activated alkenes that can succumb to deleterious pathways (e.g., a competing hydrogen evolution reaction or oligomerization) in a standard electrochemical reduction. We demonstrate herein that selective hydrogenation of the C-C π-bond of fumarate esters can be achieved via electrocatalytic CPET (eCPET) using a CPET mediator comprising cobaltocene with a tethered Brønsted base. High selectivity for electrocatalytic hydrogenation is observed only when the mediator is present. Mechanistic analysis sheds light on two distinct kinetic regimes based on the substrate concentration: low fumarate concentrations operate via rate-limiting CPET followed by an electron-transfer/proton-transfer (ET/PT) step, whereas high concentrations operate via CPET followed by a rate-limiting ET/PT step.
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Affiliation(s)
- Joseph Derosa
- Division of Chemistry and Chemical Engineering, California Institute of Technology (Caltech), Pasadena, California 91125, United States
| | - Pablo Garrido-Barros
- Division of Chemistry and Chemical Engineering, California Institute of Technology (Caltech), Pasadena, California 91125, United States
| | - Jonas C Peters
- Division of Chemistry and Chemical Engineering, California Institute of Technology (Caltech), Pasadena, California 91125, United States
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19
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Yang X, Zhuang Y, Zhu J, Le J, Cheng J. Recent progress on multiscale modeling of electrochemistry. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2021. [DOI: 10.1002/wcms.1559] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Xiao‐Hui Yang
- State Key Laboratory of Physical Chemistry of Solid Surfaces iChEM, College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Yong‐Bin Zhuang
- State Key Laboratory of Physical Chemistry of Solid Surfaces iChEM, College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Jia‐Xin Zhu
- State Key Laboratory of Physical Chemistry of Solid Surfaces iChEM, College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
| | - Jia‐Bo Le
- Ningbo Institute of Materials Technology and Engineering Chinese Academy of Sciences Ningbo China
| | - Jun Cheng
- State Key Laboratory of Physical Chemistry of Solid Surfaces iChEM, College of Chemistry and Chemical Engineering, Xiamen University Xiamen China
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20
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Cook AW, Emge TJ, Waldie KM. Insights into Formate Oxidation by a Series of Cobalt Piano-Stool Complexes Supported by Bis(phosphino)amine Ligands. Inorg Chem 2021; 60:7372-7380. [PMID: 33904730 DOI: 10.1021/acs.inorgchem.1c00563] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A series of (cyclopentadienyl)cobalt(III) half-sandwich complexes (1-4) supported by bidentate bis(phosphino)amine ligands was synthesized and characterized by NMR spectroscopy, X-ray crystallography, and cyclic voltammetry. The CoIII-hydride complex 4-H bearing the bis(cyclohexylphosphine) ligand derivative was successfully isolated via protonation of the neutral reduced CoI complex 5 with a weak acid. Experimental and computational methods were used to determine the thermodynamic hydride accepting ability of these CoIII centers and to evaluate their reactivity toward the oxidation of formate. We find that the hydride accepting ability of 1-4 ranges from 71 to 74 kcal/mol in acetonitrile, which should favor a highly exergonic reaction with formate through direct hydride transfer. Formate oxidation was demonstrated at elevated temperatures in the presence of stoichiometric quantities of 4, generating carbon dioxide and the CoIII-hydride complex 4-H in 72% yield.
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Affiliation(s)
- Andrew W Cook
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
| | - Thomas J Emge
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
| | - Kate M Waldie
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903, United States
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