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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Non Linear Optical, Thermodynamic Analysis and Spectroscopic Investigation of GPA Optical Materials

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.730.106 ◽

2017 ◽

Vol 730 ◽

pp. 106-111

Author(s):

Xiao Jing Liu ◽

Xin Sun ◽

Jing Hua Guo

Keyword(s):

Optical Materials ◽

Density Functional ◽

Nonlinear Optical ◽

Energy Gap ◽

Chemical Reactivity ◽

Nbo Analysis ◽

Basis Sets ◽

Nucleophilic Attack ◽

Charge Delocalization ◽

Different Temperatures

In this work, density functional theory (DFT) calculations with B3LYP/6-311++G(d,p) basis sets was used to explore the electronic, structural, nonlinear optical and thermal properties aspects of glycine-phthalic acid (GPA) optical materials. Dipole moment, static polarizability and first hyperpolarizability analysis of the molecule have been performed. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. MEP study confirms GPA as an electron rich species and explains its electrophilic nature. MEP shows that this molecule has several possible sites for electrophilic/nucleophilic attack in which V(r) calculations provide insights into the order of preference. The low value of HOMO-LUMO energy gap reflects the high chemical reactivity, low chemical stability and hardness of GPA molecule. Thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp), standard entropies (S) and standard enthalpy (H) increase with rise in temperature. These results discussed in this study will upsurge the knowledge to design and synthesize new type nonlinear optical materials with exceptional chemical and physical properties.

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

10.26434/chemrxiv.14035625 ◽

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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Dioxirane oxidation of nitrosoamines. An ab initio study

Canadian Journal of Chemistry ◽

10.1139/v98-217 ◽

1999 ◽

Vol 77 (1) ◽

pp. 74-85 ◽

Cited By ~ 2

Author(s):

Gennady V Shustov ◽

Arvi Rauk

Keyword(s):

Ab Initio ◽

Density Functional ◽

Activation Barrier ◽

Theoretical Method ◽

Dielectric Medium ◽

No Oxidation ◽

Basis Sets ◽

Reaction Centre ◽

Polar Solvents ◽

Amine Nitrogen

Pathways for oxidation of the parent nitrosoamine 2, nitrosodimethylamine 3, and anti- nitrosoethylmethylamine 4 by the parent dioxirane 1 have been explored computationally using the B3LYP hybrid density functional theoretical method in conjunction with the 6-31G* and 6-311+G** basis sets. Oxygen transfer from 1 to the nitrogen of the NO group (NO oxidation), yielding nitroamines 5,7, and 10, has the lowest activation barrier (15, 12.8, and 12 kcal mol-1 for 2, 3, and anti-4, respectively). Oxidation of the amine nitrogen (N oxidation) in 2, 3 leads to nitric oxide and nitroxyl radicals 6, 8 and is characterized by the highest activation energy: 28.5 kcal mol-1 for 2, 22.3 kcal mol-1 for 3. The potential barrier to hydroxylation of the methyl groups in 3 (CH oxidation) is intermediate - ca. 19 kcal mol-1. Introduction of a methyl group to the carbon reaction centre decreases the activation barrier of the anti-CH oxidation by 2-3 kcal mol-1. In 3, a gas-phase small preference for anti-CH oxidation over syn-CH oxidation, 0.1 kcal mol-1, is predicted to increase dramatically to 4.7 kcal mol-1 when the reaction is carried out in a dielectric medium (acetone, IPCM model). In general, polar solvents (CH2Cl2, acetone) lower the activation barriers for the NO, N, and CH oxidations, more so for the species of higher polarity than those of lower polarity (reactive complexes (1+3), (1+anti-4), transition state anti,syn-TSCH(1+4)]. However, the chemoselectivity (EaNO <Eaanti-CH <Easyn-CH <EaN) in the polar solvents is predicted to be the same as in the gas phase.Key words: dioxirane, nitrosoamines, oxidation, ab initio, omputation.

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Theoretical Study on the Mechanism of Reaction of Ground-State Fe Atoms with Carbon Dioxide

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20040013 ◽

2004 ◽

Vol 69 (1) ◽

pp. 13-33 ◽

Cited By ~ 9

Author(s):

Dimitrios A. Pantazis ◽

Athanassios C. Tsipis ◽

Constantinos A. Tsipis

Keyword(s):

Ground State ◽

Density Functional ◽

Activation Barrier ◽

Spectroscopic Properties ◽

Basis Sets ◽

Stationary Points ◽

Insertion Reaction ◽

Weakly Bound ◽

Satisfactory Description ◽

Bonding Properties

Density functional calculations at the B3LYP level of theory, using the 6-31G(d) and 6-311+G(3df) basis sets, provide a satisfactory description of the geometric and energetic reaction profile of the Fe + CO2 → FeO + CO reaction. The reaction is predicted to be endothermic by 23.24 kcal/mol at the B3LYP/6-311+G(3df)//B3LYP/6-31G(d) level of theory and to proceed by formation of either a Fe(η2-OCO) or a Fe(η3-OCO) intermediate. The Fe(η2-OCO) intermediate in the 5A' ground state is weakly bound with respect to Fe(5D) and CO2 dissociation products by 0.78 (2.88) kcal/mol at the B3LYP/6-31G(d) (B3LYP/6-311+ G(3df)//B3LYP/6-31G(d)) levels of theory. In contrast, the Fe(η3-OCO) intermediate in the 5A1 ground state is unbound with respect to Fe(5D) and CO2 dissociation products by 8.27 (11.15) kcal/mol at the same levels of theory. However, both intermediates are strongly bound relative to the separated Fe+(6D) and [CO2]- anion; the computed bond dissociation energies for the Fe(η2-OCO) and Fe(η3-OCO) intermediates are 207.33 and 198.28 kcal/mol in terms of ∆E0 at the B3LYP/6-31G(d), respectively. In the Fe(η2-OCO) and Fe(η3-OCO) intermediates, an intramolecular insertion reaction of the Fe atom to O-C bond takes place yielding the isomeric OFe(η1-CO) and OFe(η1-OC) products, respectively, with a relatively low activation barrier of 25.24 (21.69) and 26.36 (23.38) kcal/mol at the B3LYP/6-31G(d) (B3LYP/6-311+G(3df)//B3LYP/6-31G(d)) levels of theory, respectively. The calculated structures, relative stability and bonding properties of all stationary points are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution and harmonic vibrational frequencies.

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

10.26434/chemrxiv.14035625.v1 ◽

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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New Insight into the Chloroacetanilide Herbicide Degradation Mechanism through a Nucleophilic Attack of Hydrogen Sulfide

International Journal of Molecular Sciences ◽

10.3390/ijms19102864 ◽

2018 ◽

Vol 19 (10) ◽

pp. 2864 ◽

Cited By ~ 5

Author(s):

José Mora ◽

Cristian Cervantes ◽

Edgar Marquez

Keyword(s):

Hydrogen Sulfide ◽

Reaction Mechanism ◽

Activation Barrier ◽

Degradation Mechanism ◽

Reaction Force ◽

Transition States ◽

Reaction Coordinate ◽

Basis Sets ◽

Nucleophilic Attack ◽

Intrinsic Reaction Coordinate

The nucleophilic attack of hydrogen sulfide (HS−) on six different chloroacetanilide herbicides was evaluated theoretically using the dispersion-corrected hybrid functional wB97XD and the 6-311++G(2d,2p) Pople basis sets. The six evaluated substrates were propachlor (A), alachlor (B), metolachlor (C), tioacetanilide (D), β-anilide (E), and methylene (F). Three possible mechanisms were considered: (a) bimolecular nucleophilic substitution (SN2) reaction mechanism, (b) oxygen assistance, and (c) nitrogen assistance. Mechanisms based on O- and N-assistance were discarded due to a very high activation barrier in comparison with the corresponding SN2 mechanism, with the exception of compound F. The N-assistance mechanism for compound F had a free activation energy of 23.52 kcal/mol, which was close to the value for the corresponding SN2 mechanism (23.94 kcal/mol), as these two mechanisms could occur in parallel reactions with almost 50% of each one. In compounds A to D, an important electron-withdrawing effect of the C=O and C=S groups was seen, and consequently, the activation free energies in these SN2 reactions were smaller, with a value of approximately 18 kcal/mol. Instead, compounds E and F, which have a CH2 group in the β-position, presented a higher activation free energy (≈22 kcal/mol). Good agreement was found between experimental and theoretical values for all cases, and a reaction force analysis was performed on the intrinsic reaction coordinate profile in order to gain more details about the reaction mechanism. Finally, from the natural bond orbital (NBO) analysis, it was possible to evaluate the electronic reorganization through the reaction pathway where all the transition states were early in nature in the reaction coordinate (δBav < 50%); the transition states corresponding to compounds A to D turned out to be more synchronous than those for compounds E and F.

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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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Experimental and Theoretical (ab initio and DFT) Analysis of UV-Vis Spectra, Thermodynamic Functions and Non-linear Optical Properties of 2-Chloro-3,4-Dimethoxybenzaldehyde

JOURNAL OF ADVANCES IN PHYSICS ◽

10.24297/jap.v8i2.1519 ◽

2015 ◽

Vol 8 (2) ◽

pp. 2122-2134

Author(s):

Sarvendra Kumar ◽

Rajesh Kumar ◽

Jayant Teotia ◽

M. K. Yadav

Keyword(s):

Thermodynamic Functions ◽

Title Compound ◽

Density Functional ◽

Structural Characteristics ◽

Basis Sets ◽

Ultraviolet Absorption Spectrum ◽

Non Linear ◽

Different Temperatures ◽

Linear Optical Properties ◽

Linear Optical

In the present work, UV- Visible spectra of 2-Chloro-3,4-Dimethoxybenzaldehyde (2,3,4-CDMB) compoundÂ have been carried out experimentally and theoretically. The ultraviolet absorption spectrum of title compound in three solvents (Acetone, Diethyl Ether, CCl4) of different polarity were examined in the range of 200â€“500 nm. The structure of the molecule was optimized and the structural characteristics were determined by HF and DFT (B3LYP) methods with 6-31+G(d,p) and 6-311++G(d,p) as basis sets. The excitation energy, wavelength corresponds to absorption maxima () and oscillator strength (f) are calculated by Time-Dependent Density Functional Theory (TD-DFT) using B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) as basis sets. The electric dipole moment (Î¼), polarizability (Î±) and the first hyperpolarizability (Î² ) have been computed to evaluate the non-linear optical (NLO) response of the investigated compound by HF and DFT (B3LYP) with already mentioned basis sets. Thermodynamic functions of the title compound at different temperatures were also calculated.

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Hydrostibination of Alkynes: A Radical Mechanism

10.26434/chemrxiv.12497834 ◽

2020 ◽

Author(s):

Josh MacMillan ◽

Katherine Marczenko ◽

Erin Johnson ◽

Saurabh Chitnis

Keyword(s):

Density Functional ◽

Activation Barrier ◽

Closed Shell ◽

Reaction Rates ◽

Radical Mechanism ◽

Neutral Radical ◽

Kinetic Isotope ◽

Rate Limiting Step ◽

Ionic Mechanisms ◽

Terminal Acetylenes

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical SbII and SbIII intermediates. Density Functional Theory (DFT) calculations are consistent this model, predicting an activation barrier that is within 1 kcal mol-1 of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring SbII and SbIII intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as E-olefins.

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