Amphoteric Lewis Acid/base Activity Enables an Unprecedented Pathway for Low-Energy C-O Cleavage in the Electrocatalytic Reduction of Carbon Dioxide

Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, the cleavage of C-O bond in the intermediate largely contributing to this phenomenon. Additional Lewis acids have been shown to aid in weakening the C-O bond. We herein present computational and experimental evidence, with ruthenium polypyridyl based CO2 reduction electrocatalysts, for a mechanistic route that involves one metal center acting as both Lewis base and Lewis acid at different stages of the catalytic cycle. The Lewis basic character of Ru is seen in the initial nucleophilic attack at CO2 to form [Ru-CO2]0, while its Lewis acid character allows the formation of a 5-membered metallacyclic intermediate, [Ru-CO2CO2]0,c, by intramolecular cyclization of a linear [Ru-CO2CO2]0 species that is formed from [Ru-CO2]0 and a second equivalent of CO2. [Ru-CO2CO2]0,c is crucial for energy-conserving turnover, as it allows for a third reduction at a more positive potential than that of the starting complex Ru2+. The calculated activation barrier for C-O bond cleavage in [Ru-CO2CO2]-1,c is dramatically decreased to 10.5 kcal mol-1 from 60 kcal mol-1, the latter required for C-O bond cleavage in the linear intermediate [Ru-CO2CO2]0. The intermediates are characterized experimentally by FT-IR and 13C NMR spectroscopy during electrocatalytic turnover and are corroborated by density functional theory (DFT).

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Alternating substrate/ligand-metal coordination enables a low-energy pathway for C-O bond cleavage in the electrocatalytic reduction of carbon dioxide

10.26434/chemrxiv.14035625.v2 ◽

2021 ◽

Author(s):

Hemlata Agarwala ◽

Xiaoyu Chen ◽

Julien R. Lyonnet ◽

Ben A Johnson ◽

Mårten Ahlquist ◽

...

Keyword(s):

Lewis Acid ◽

Lewis Acids ◽

Density Functional ◽

Activation Barrier ◽

Bond Cleavage ◽

Lewis Base ◽

Nucleophilic Attack ◽

Co Conversion ◽

Energy Conserving ◽

Ft Ir

Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, the cleavage of C-O bond in the intermediate largely contributing to this phenomenon. Additional Lewis acids have been shown to aid in weakening the C-O bond. We herein present computational and experimental evidence, with ruthenium polypyridyl based CO2 reduction electrocatalysts, for a mechanistic route that involves one metal center acting as both Lewis base and Lewis acid at different stages of the catalytic cycle. The Lewis basic character of Ru is seen in the initial nucleophilic attack at CO2 to form [Ru-CO2]0, while its Lewis acid character allows the formation of a 5-membered metallacyclic intermediate, [Ru-CO2CO2]0,c, by intramolecular cyclization of a linear [Ru-CO2CO2]0 species that is formed from [Ru-CO2]0 and a second equivalent of CO2. [Ru-CO2CO2]0,c is crucial for energy-conserving turnover, as it allows for a third reduction at a more positive potential than that of the starting complex Ru2+. The calculated activation barrier for C-O bond cleavage in [Ru-CO2CO2]-1,c is dramatically decreased to 10.5 kcal mol-1 from 60 kcal mol-1, the latter required for C-O bond cleavage in the linear intermediate [Ru-CO2CO2]0. The intermediates are characterized experimentally by FT-IR and 13C NMR spectroscopy during electrocatalytic turnover and are corroborated by density functional theory (DFT).

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The structure and activity of potassium supported on SBA-15 molecular sieve: Density functional theory study

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633613500764 ◽

2014 ◽

Vol 13 (01) ◽

pp. 1350076 ◽

Cited By ~ 2

Author(s):

Bing Liu ◽

Daxi Wang ◽

Zhongxue Wang ◽

Zhen Zhao ◽

Yu Chen ◽

...

Keyword(s):

Density Functional Theory ◽

Lewis Acid ◽

Molecular Sieve ◽

Active Sites ◽

Density Functional ◽

Structural Model ◽

Vibrational Frequencies ◽

Oxygen Molecule ◽

Lewis Base ◽

Functional Theory

The geometries, vibrational frequencies, electronic properties and reactivity of potassium supported on SBA-15 have been theoretically investigated by the density functional theory (DFT) method. The structural model of the potassium supported on SBA-15 was constructed based on our previous work [Wang ZX, Wang DX, Zhao Z, Chen Y, Lan J, A DFT study of the structural units in SBA-15 mesoporous molecular sieve, Comput. Theor. Chem.963, 403, 2011]. This paper is the extension of our previous work. The most favored location of potassium atom was obtained by the calculation of substitution energy. The calculated vibrational frequencies of K /SBA-15 are in good agreement with the experimental results. By analyzing the properties of electronic structure, we found that the O atom of Si - O (2)- K group acts as the Lewis base center and the K atom acts as the Lewis acid center. The reactivity of K /SBA-15 was investigated by calculating the activation of oxygen molecule. The oxygen molecule can be activated by K /SBA-15 with an energy barrier of 103.2 kJ/mol. In the final state, the activated oxygen atoms become new Lewis acid centers, which are predicted to act as the active sites in the catalytic reactions. This study provides a deep insight into the properties of supported potassium catalysts and offers fundamental information for further research.

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Fluorinated 9-borafluorenes vs. conventional perfluoroaryl boranes Comparative Lewis acidity

Canadian Journal of Chemistry ◽

10.1139/v05-240 ◽

2005 ◽

Vol 83 (12) ◽

pp. 2098-2105 ◽

Cited By ~ 32

Author(s):

Preston A Chase ◽

Patricio E Romero ◽

Warren E Piers ◽

Masood Parvez ◽

Brian O Patrick

Keyword(s):

Key Words ◽

Lewis Acid ◽

Lewis Acids ◽

Acid Strength ◽

Lewis Base ◽

Lewis Acidity ◽

Electrochemical Studies ◽

Steric Factors

Perfluorinated 9-phenyl-9-borafluorene, 1, is an antiaromatic analog of the well-known tris(pentafluorophenyl)borane. Spectroscopic, structural, and electrochemical studies have been performed on 1 and its Lewis base adducts with MeCN, THF, and PMe3 with a view to assessing its comparative Lewis acid strength relative to B(C6F5)3. For the sterically undemanding Lewis base MeCN, 1 and B(C6F5)3 have comparable LA strengths, while for more sterically prominent THF, 1 is clearly the stronger Lewis acid (LA) based on competition experiments. We conclude that steric factors, rather than antiaromaticity, are the most important determinants in the LA strength differences between 1 and B(C6F5)3.Key words: boranes, Lewis acids, fluorinated compounds, heterocycles.

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Homogeneous Gold Catalysis: Mechanistic Investigation of Hydroalkoxylation of Various Alkynes

10.26686/wgtn.17009375.v1 ◽

2021 ◽

Author(s):

◽

Zhi Xiang Wong

Keyword(s):

Density Functional ◽

Activation Barrier ◽

Gold Atom ◽

Gold Catalysis ◽

Basis Sets ◽

Nucleophilic Attack ◽

Enol Ether ◽

Hydrogen Migration ◽

Mechanistic Investigation ◽

Internal Alkyne

The reaction mechanism of the gold(III)-catalysed hydroalkoxylation of alkynes is studied to provide a deeper understanding of homogeneous gold catalysis. The study is conducted computationally using Density Functional Theory (DFT), with the PBE0 and BP86 functionals and basis sets of triple-ζ quality (aug-cc-pVTZ and aug-cc-pVTZ-PP for the gold atom). It emphasises the mechanisms undergone by various alkynes when they are activated by gold(III) catalysts towards nucleophilic attack to first form an enol ether and followed by a second nucleophilic attack to form a ketal as the final product. Hydrogen bonding networks formed by the solvent methanols are found to play a crucial role in the mechanism especially in the hydrogen migration steps that follow after the nucleophilic attacks. The first nucleophilic attacks are predicted to have rather low activation energies and hence they are expected to proceed fast while the second additions vary in activation barriers, depending on the steric effects in the substrates. The activation barrier for the last hydrogen migration is highest for all of the three reactions investigated and is expected to be the rate determining step. Investigations of internal alkyne reactions reveal that each elementary step requires a higher activation energy compared to terminal alkynes, which explains the low experimental rate of such reactions. Due to the regioselectivity problem in internal alkyne reactions, this results in a mixture of products which is difficult to isolate due to the similarities in their reaction energies. The study also highlights the calculated thermodynamics and kinetics of the reactions, which can be useful in predicting experimental outcomes. Arrhenius plots of concentration of each intermediate species against time were produced to further help the understanding of these mechanisms, whether or not the reactions go to full completion or stop at the formation of enol ether.

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Asymmetric synthesis based on chiral (arene)tricarbonylchromium acetal complexes. Addition reactions to the ortho-formyl complex

Canadian Journal of Chemistry ◽

10.1139/v00-150 ◽

2000 ◽

Vol 78 (12) ◽

pp. 1629-1636 ◽

Cited By ~ 5

Author(s):

M Kevin McKay ◽

James R Green

Keyword(s):

Asymmetric Synthesis ◽

Lewis Acid ◽

Lewis Acids ◽

Nucleophilic Attack ◽

Addition Reactions ◽

Trans Conformation ◽

Enantiomerically Pure ◽

The Face ◽

Monodentate Coordination ◽

Tricarbonylchromium Complexes

The addition reactions of organolithium and Grignard reagents to chiral, enantiomerically pure ortho-formyl (arene)tricarbonylchromium acetal complex (2) have been studied. The diastereoselectivity of the addition process is fair in the absence of an additional Lewis acid, and good in the presence of Ti(OiPr)4. The nature of the newly formed chiral centre, and studies on the possible nature of the nucleophilic species suggest that the Lewis acid acts through monodentate coordination to the aldehyde carbonyl, and thereby alters the carbonyl rotamer population more heavily in favour of the s-trans conformation. Nucleophilic attack then occurs on the face anti- to that bearing the Cr(CO)3 unit.Key words: (arene)tricarbonylchromium complexes, asymmetric synthesis, carbonyl additions, Lewis acids.

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Lowering the C-H Bond Activation Barrier of Methane Using SAC@Cu(111): A Periodic DFT Investigations

10.33774/chemrxiv-2021-zfrcn ◽

2021 ◽

Author(s):

Meema Bhati ◽

Jignesh Dhumal ◽

Kavita Joshi

Keyword(s):

Density Functional ◽

Bond Activation ◽

Activation Barrier ◽

Bond Cleavage ◽

Minimum Energy ◽

Value Added ◽

Methane Activation ◽

Single Atom ◽

Activation Barriers ◽

Metal Doped

Methane has long captured the world's spotlight for being the simplest and yet one of the most notorious hydrocarbon. Exploring its potential to be converted into value added products has raised a compelling interest. In the present work, we have studied the efficiency of Single-Atom Catalysts (SACs) for methane activation employing Density Functional Theory (DFT). The Climbing Image-Nudged Elastic Bond (CI-NEB) method is used in tandem with the Improved Dimer (ID) method to determine the minimum energy pathway for the first C-H bond dissociation of methane. Our study reported that the transition-metal doped Cu(111) surfaces enhance adsorption, activate C-H bond, and reduce activation barrier for first C-H bond cleavage of methane. The results suggest Ru/Co/Rh doped Cu(111) as promising candidates for methane activation with minimal activation barrier and less endothermic reaction. For these SACs, the calculated activation barriers for first C-H bond cleavage are 0.17 eV, 0.24 eV, and 0.26 eV respectively, which is substantially lower than 1.13 eV, the activation barrier for Cu(111).

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3,3′-Bithiophene-Based Chiral Bisphosphine Oxides as Organocatalysts in Silicon-Derived Lewis Acid Mediated Reactions

Synlett ◽

10.1055/s-0039-1690777 ◽

2020 ◽

Vol 31 (06) ◽

pp. 535-546

Author(s):

Sergio Rossi ◽

Tiziana Benincori ◽

Laura Maria Raimondi ◽

Maurizio Benaglia

Keyword(s):

Lewis Acid ◽

Lewis Acids ◽

Silicon Tetrachloride ◽

Lewis Base ◽

Organic Reactions ◽

Phosphine Oxides ◽

Type Reaction

This account summarizes the development of new biheteroaromatic chiral bisphosphine oxides. 3,3′-Bithiophene-based phosphine oxides (BITIOPOs) have been successfully used as organocatalysts to promote Lewis base catalyzed, Lewis acid mediated stereoselective transformations. These highly electron-rich compounds, in combination with trichorosilyl derivatives (allyltrichlorosilane and silicon tetrachloride), generate hypervalent silicon species that act as chiral Lewis acids in highly diastereo- and enantioselective organic reactions. Several relevant examples related to these applications are discussed in detail.1 Introduction2 The BITIOPO Family3 Enantioselective Opening of Epoxides4 Enantioselective Allylation of Aldehydes5 Stereoselective Direct (Double) Aldol-Type Reaction with Ketones6 Stereoselective Direct Aldol-Type Reaction with Ester Derivatives7 Conclusions

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Recent Advances in Water-Tolerance in Frustrated Lewis Pair Chemistry

Synthesis ◽

10.1055/s-0037-1609843 ◽

2018 ◽

Vol 50 (09) ◽

pp. 1783-1795 ◽

Cited By ~ 17

Author(s):

Michael Ingleson ◽

Valerio Fasano

Keyword(s):

Small Molecules ◽

Lewis Acid ◽

Lewis Acids ◽

Short Review ◽

Lewis Base ◽

Small Molecule Activation ◽

Significant Progress ◽

Water Tolerance ◽

Frustrated Lewis Pair ◽

Main Challenge

A water-tolerant frustrated Lewis pair (FLP) combines a sterically encumbered Lewis acid and Lewis base that in synergy are able to activate small molecules even in the presence of water. The main challenge introduced by water comes from its reversible coordination to the Lewis acid which causes a marked increase in the Brønsted acidity of water. Indeed, the oxophilic Lewis acids typically used in FLP chemistry form water adducts whose acidity can be comparable to that of strong Brønsted acids such as HCl, thus they can protonate the Lewis base component of the FLP. Irreversible proton transfer quenches the reactivity of both the Lewis acid and the Lewis base, precluding small molecule activation. This short review discusses the efforts to overcome water-intolerance in FLP systems, a topic that in less than five years has seen significant progress.1 Introduction2 Water-Tolerance (or Alcohol-Tolerance) in Carbonyl Reductions3 Water-Tolerance with Stronger Bases4 Water-Tolerant Non-Boron-Based Lewis Acids in FLP Chemistry5 Conclusions

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Homogeneous Gold Catalysis: Mechanistic Investigation of Hydroalkoxylation of Various Alkynes

10.26686/wgtn.17009375 ◽

2021 ◽

Author(s):

◽

Zhi Xiang Wong

Keyword(s):

Density Functional ◽

Activation Barrier ◽

Gold Atom ◽

Gold Catalysis ◽

Basis Sets ◽

Nucleophilic Attack ◽

Enol Ether ◽

Hydrogen Migration ◽

Mechanistic Investigation ◽

Internal Alkyne

The reaction mechanism of the gold(III)-catalysed hydroalkoxylation of alkynes is studied to provide a deeper understanding of homogeneous gold catalysis. The study is conducted computationally using Density Functional Theory (DFT), with the PBE0 and BP86 functionals and basis sets of triple-ζ quality (aug-cc-pVTZ and aug-cc-pVTZ-PP for the gold atom). It emphasises the mechanisms undergone by various alkynes when they are activated by gold(III) catalysts towards nucleophilic attack to first form an enol ether and followed by a second nucleophilic attack to form a ketal as the final product. Hydrogen bonding networks formed by the solvent methanols are found to play a crucial role in the mechanism especially in the hydrogen migration steps that follow after the nucleophilic attacks. The first nucleophilic attacks are predicted to have rather low activation energies and hence they are expected to proceed fast while the second additions vary in activation barriers, depending on the steric effects in the substrates. The activation barrier for the last hydrogen migration is highest for all of the three reactions investigated and is expected to be the rate determining step. Investigations of internal alkyne reactions reveal that each elementary step requires a higher activation energy compared to terminal alkynes, which explains the low experimental rate of such reactions. Due to the regioselectivity problem in internal alkyne reactions, this results in a mixture of products which is difficult to isolate due to the similarities in their reaction energies. The study also highlights the calculated thermodynamics and kinetics of the reactions, which can be useful in predicting experimental outcomes. Arrhenius plots of concentration of each intermediate species against time were produced to further help the understanding of these mechanisms, whether or not the reactions go to full completion or stop at the formation of enol ether.

Download Full-text

Amphoteric Lewis Acid/base Activity Enables an Unprecedented Pathway for Low-Energy C-O Cleavage in the Electrocatalytic Reduction of Carbon Dioxide