Mechanistic Insights from Density Functional Theory into Rh/Acid-Catalyzed Synthesis of 1,2-Dihydroquinolines via Skeleton-Reorganizing Coupling of Cycloheptatriene and Amines.

Density functional theory calculations were conducted to refine our understanding at the molecular level of the synthesis of fused 1,2-dihydroquinolines through Rh- and acid-catalyzed skeleton-reorganizing coupling reactions of cycloheptatriene with amines. The results reveal that the reaction progresses via cascade catalysis, consisting of consecutive steps of Rh-catalyzed intermolecular coupling involving two Rh-Rh-Rh transformations with a maximum energy barrier of 27.1 kcal/mol, followed by acid-catalyzed intramolecular skeleton reorganization with a peak energy barrier of 23.

DFT Calculations Rationalize Unconventional Regioselectivity in Pd-Catalyzed Defluorinative Alkylation of -Difluorocyclopropanes with Hydrazones.

Density functional theory (DFT) calculations have been conducted to gain insight into the unique formation of the branched alkylation product in the Pd-catalyzed defluorinative alkylation of -difluorocyclopropanes with hydrazones. The reaction is established to occur in sequence through oxidative addition, β-F elimination, η-η isomerization, transmetalation, η-η isomerization, 3,3'-reductive elimination, deprotonation/N extrusion, and proton abstraction. The rate-determining step of the reaction is identified as the β-F elimination, featuring an energy barrier of 28.

Theoretical Insight into the Palladium-Catalyzed Prenylation and Geranylation of Oxindoles with Isoprene.

This work presents a comprehensive mechanistic study of the ligand-controlled palladium-catalyzed prenylation (with C added) and geranylation (with C added) reactions of oxindole with isoprene. The calculated results indicate that the prenylation with the bis-phosphine ligand and geranylation with the monophosphine ligand fundamentally share a common mechanism. This mechanism involves the formation of two crucial species: a η-allyl-Pd(II) cation and an oxindole carbon anion.

Density Functional Theory Study of Gold-Catalyzed 1,2-Diarylation of Alkenes: π-Activation Migratory Insertion Mechanisms.

Density functional theory calculations are carried out to better understand the first gold-catalyzed 1,2-diarylation reactions of alkenes reported in the recent literature. The calculations on two representative reactions, aryl alkene/aryl iodide coupling pair (the aryl-I bond is located outside the aryl alkene) versus iodoaryl alkene/indole coupling pair (the aryl-I bond is located in the aryl alkene), confirm that the reaction involves a π-activation mechanism rather than the general migratory insertion mechanism in previously known metal catalysis by Pd, Ni, and Cu complexes. Theoretical results rationalize the regioselectivity of the reactions controlled by the aryl-I bond position (intermolecular or intramolecular) and also the ligand and substituent effects on the reactivity.

DFT Mechanistic Study of Ir/Ni-Metallaphotoredox-Catalyzed Difluoromethylation of Aryl Bromides.

The work by MacMillan et al. ( 2018, 57, 12543-12548) developed an Ir/Ni-metallaphotoredox-catalyzed difluoromethylation strategy of aryl bromides using CHFBr as the CHF reagent in the presence of tris(trimethylsilyl)silane. Here, we present a density functional theory (DFT)-based computational study to understand special dual catalysis promoting the C(sp)-C(sp) coupling.

Mechanistic Insight into Palladium-Catalyzed γ-C(sp)-H Arylation of Alkylamines with 2-Iodobenzoic Acid: Role of the -Carboxylate Group.

Density functional theory calculations were performed to understand the distinctly different reactivities of carboxylate-substituted aryl halides and pristine aryl halides toward the Pd-catalyzed γ-C(sp)-H arylation of secondary alkylamines. It is found that, when 2-iodobenzoic acid (a representative of -carboxylate-substituted aryl halides) is used as an aryl transfer agent, the arylation reaction is energetically favorable, while when the pristine aryl halide iodobenzene is used as the aryl transfer reagent, the reaction is kinetically difficult. Our calculations showed an operative Pd/Pd/Pd redox cycle, which differs in the mechanistic details from the cycle proposed by the experimental authors.

DFT Study on Photosensitizer-Free Visible-Light-Mediated Au-Catalyzed -Difunctionalization of Alkynes: Mechanism and Selectivities as Compared to Rh Catalysis.

Density functional theory (DFT) calculations were performed to investigate the photosensitizer-free visible-light-mediated gold-catalyzed -difunctionalization of alkynes with aryl diazonium salts. The detailed reaction mechanism is established, and the observed regio- and chemoselectivities are rationalized. The results are compared to those of the rhodium-catalyzed -difunctionalization of alkynes.

Mechanistic Study on the Decarboxylative C-N Cross-Coupling between Alkyl Carboxylic Acids and Nitrogen Nucleophiles via Dual Copper and Photoredox Catalysis.

This work presents a density functional theory (DFT)-based theoretical study on the cross-coupling reaction of alkyl carboxylic acids and nitrogen nucleophiles via dual copper and photoredox catalysis developed by MacMillan et al. [, , 559, 83-87]. The calculations showed the mechanistic details of three subprocesses proposed in the experimental study, including production of alkyl radicals, iridium(III) photoredox cycle, and copper(I) thermalredox cycle.

Theoretical Insight into the Mechanism and Origin of Divergent Reactivity in the Synthesis of Benzo-Heterocycles from -Alkynylbenzamides Catalyzed by Gold and Platinum Complexes.

This work presents a DFT study on the mechanism and origin of catalyst-controlled divergent reactivity in the synthesis of benzo-heterocycles from -alkynylbenzamides by Au(I)/Pt(IV) catalysis. The results indicate that the transformations proceed via a nucleophilic cyclization process. In the Au(I) catalysis, the preferred -attack mode mainly originates from the symmetry match in the dominant bond-forming interaction between the lone-pair orbital of carbonyl-O and the in-plane alkyne π* orbital, and the electronic property of the ligand controls the -5--/-6-- selectivity.

Theoretical Insight into the Au(I)-Catalyzed Intermolecular Condensation of Homopropargyl Alcohols with Terminal Alkynes: Reactant Stoichiometric Ratio-Controlled Chemodivergence.

The mechanisms and chemoselectivities on the Au(I)-catalyzed intermolecular condensation between homopropargyl alcohols and terminal alkynes were investigated by performing DFT calculations. The reaction was indicated to involve three stages: transformation of the homopropargyl alcohol (R) via intramolecular cyclization to the cyclic vinyl ether (R'), formation of the C-2-arylalkynyl cyclic ether (P) via hydroalkynylation of R' with phenylacetylene (R), and conversion from P to 2,3-dihydro-oxepine (P). The results revealed the origin of the reaction divergence and rationalized the experimental observations that a 1:3 reactant stoichiometric ratio affords P as the major product, whereas the 1:1.

Cleavage of the β-O-4 bond in a lignin model compound using the acidic ionic liquid 1-H-3-methylimidazolium chloride as catalyst: a DFT mechanistic study.

Understanding the mechanism for the catalyzed cleavage of the β-O-4 ether linkage in lignin is crucial to developing efficient strategies for depolymerizing lignin. In this work, veratrylglycerol-β-guaiacyl ether (VG) was used as a lignin model compound in a theoretical investigation of the mechanism for the cleavage of the β-O-4 bond as catalyzed by the acidic ionic liquid (IL) 1-H-3-methylimidazolium chloride ([HMIM]Cl). The reaction was found to involve two processes-dehydration and hydrolysis-in which the cation functions as a Brønsted acid (donating a proton) and the anion acts as a nucleophile (promoting dehydration) or interacts with the substrate through hydrogen bonding, stabilizing the intermediate.

Where do photogenerated holes at the g-CN/water interface go for water splitting: HO or OH?

Graphitic carbon nitride (g-C3N4), a metal-free two-dimensional photocatalyst, has drawn increasing attention due to its application in photocatalytic water splitting. However, its quantum efficiency is limited by the poor performance of the oxygen evolution reaction (OER). Therefore, it is important to clarify the behavior of photogenerated holes in the OER.

The Dual Role of Gold(I) Complexes in Photosensitizer-Free Visible-Light-Mediated Gold-Catalyzed 1,2-Difunctionalization of Alkynes: A DFT Study.

Recently, a photosensitizer-free visible-light-mediated gold-catalyzed 1,2-difunctionalization of alkynes has been developed. However, mechanistic aspects of this unconventional photocatalytic reaction remain largely obscure. With the aid of density functional theory (DFT) and time-dependent (TD)DFT calculations, we mimicked the photosensitizer-free visible-light-mediated gold-catalyzed 1,2-difunctionalization of 1-phenyl-1-hexyne and focused on two fundamental questions: how does photoredox catalysis occur without assistance of an exogenous photosensitizer under visible light irradiation, and what is the detailed mechanism of the gold-catalyzed 1,2-difunctionalization of alkynes? The results reveal the dual role of the gold(I) complex in light-harvesting and catalysis, where a charge-transfer (CT) complex formed by the association of gold(I) catalyst with PhN BF acts as a photosensitizer, which can undergo an electronic transition between the gold(I) moiety and PhN BF of the CT complex into an excited electronic state and afford a charge-transfer exciplex.

Theoretical insight into the mechanism, regioselectivity, and substituent group effect of Rh-catalyzed synthesis of 1,2-benzothiazines from NH-sulfoximines and diazo compounds.

This work presents a computational study of RhIII-catalyzed synthesis of 1,2-benzothiazines from NH-sulfoximines and diazo compounds reported by Bolm et al. (Angew. Chem.

Theoretical Insight into the Mechansim and Origin of Ligand-Controlled Regioselectivity in Homogenous Gold-Catalyzed Intramolecular Hydroarylation of Alkynes.

This work aims at understanding the mechanism and regioselectivity in ligand-controlled gold-catalyzed divergent intramolecular hydroarylation of alkynes reported by Jiang et al. ( J. Am.

Bidirectional Electron-Transfer in Polypeptides with Various Secondary Structures.

The protein-mediated bidirectional electron transfer (ET) is the foundation of protein molecular wire, and plays an important role in the rapid detection of oxo-guanine-adenine DNA mismatches by MutY glycosylase. However, the influences of structural transitions on bidirectional ET are still not clear. In this work, the modified through-bond coupling (MTBC) model was further refined to correlate the structural transition and ET rate more quantitatively.

Theoretical Elucidation of the Mechanism and Kinetic Experimental Phenomena on the Esterification of α-Tocopherol with Succinic Anhydride: Catalysis of a Histidine Derivative vs an Imidazolium-Based Ionic Liquid.

DFT calculations have been conducted to gain insight into the mechanism and kinetics of the esterification of α-tocopherol with succinic anhydride catalyzed by a histidine derivative or an imidazolium-based ionic liquid (IL). The two catalytic reactions involve an intrinsically consistent molecular mechanism: a rate-determining, concerted nucleophilic substitution followed by a facile proton-transfer process. The histidine derivative or the IL anion is shown to play a decisive role, acting as a Brönsted base by abstracting the hydroxyl proton of α-tocopherol to favor the nucleophilic substitution of the hydroxyl oxygen of α-tocopherol on succinic anhydride.

DFT Study on the Formation Mechanism of Normal and Abnormal N-Heterocyclic Carbene-Carbon Dioxide Adducts from the Reaction of an Imidazolium-Based Ionic Liquid with CO.

To illustrate the formation mechanism of normal and abnormal N-heterocyclic carbene-carbon dioxide adducts (NHC-CO and aNHC-CO), we implement density functional theory calculations on the reactions of two imidazolium-based ionic liquids ([CCIm][OAc] and [CCIm][CHSO]) with CO. The reaction of [CCIm][OAc] with CO is mimicked using the gas phase model, implicit solvent model, and combined explicit-implicit solvent model. In the gas phase, the calculated barriers at 125 °C and 10 MPa are 12.

The mechanism for the formation of OH radicals in condensed-phase water under ultraviolet irradiation.

Irradiation on liquid water and ice by ultraviolet light in the range of 150-200 nm can create volatile OH radicals which react with other organic and inorganic molecules actively. However, the mechanism for OH radical formation in the condensed-phase water in this energy range is still unclear. To uncover this mechanism we studied the excited-state behaviors of ice using first-principles calculations based on many-body Green's function theory.

Modeling interactions between a β-O-4 type lignin model compound and 1-allyl-3-methylimidazolium chloride ionic liquid.

Aiming at understanding the molecular mechanism of the lignin dissolution in imidazolium-based ionic liquids (ILs), this work presents a combined quantum chemistry (QC) calculation and molecular dynamics (MD) simulation study on the interaction of the lignin model compound, veratrylglycerol-β-guaiacyl ether (VG) with 1-allyl-3-methylimidazolium chloride ([Amim]Cl). The monomer of VG is shown to feature a strong intramolecular hydrogen bond, and its dimer is indicated to present important π-π stacking and intermolecular hydrogen bonding interactions. The interactions of both the cation and anion of [Amim]Cl with VG are shown to be stronger than that between the two monomers, indicating that [Amim]Cl is capable of dissolving lignin.

Theoretical Insight into the Conversion Mechanism of Glucose to Fructose Catalyzed by CrCl in Imidazolium Chlorine Ionic Liquids.

To better understand the efficient transformation of glucose to fructose catalyzed by chromium chlorides in imidazolium-based ionic liquids (ILs), density functional theory calculations have been carried out on a model system which describes the catalytic reaction by CrCl in 1,3-dimethylimidazolium chlorine (MMImCl) ionic liquid (IL). The reaction is shown to involve three fundamental processes: ring opening, 1,2-H migration, and ring closure. The reaction is calculated to exergonic by 3.

New Insight into the Formation Mechanism of Imidazolium-Based Ionic Liquids from N-Alkyl Imidazoles and Halogenated Hydrocarbons: A Polar Microenvironment Induced and Autopromoted Process.

To illustrate the formation mechanism of imidazolium-based ionic liquids (ILs) from N-alkyl imidazoles and halogenated hydrocarbons, density functional theory calculations have been carried out on a representative system, the reaction of N-methyl imidazole with chloroethane to form 1-ethyl-3-methyl imidazolium chloride ([Emim]Cl) IL. The reaction is shown to proceed via an S2 transition state with a free energy barrier of 34.4 kcal/mol in the gas phase and 27.

Optical properties of acene molecules and pentacene crystal from the many-body Green's function method.

Acene is a type of important organic semiconductor which has promising applications in various optoelectronic devices. The fission of a singlet to triplet in it has been expected to elevate the quantum efficiency of organic solar cells. However, the quantum efficiency is still very low and the fission process is still under debate.

Spin-state energies of heme-related models from spin-flip TDDFT calculations.

Spin-state energies of heme-related models are of vital importance in biochemistry. To compute the energies of different spin states, the traditional ΔSCF method based on the density functional theory (DFT) is usually employed. In this work, the spin-flip TDDFT (SF-TDDFT) approach is investigated to compute the spin-state energies, with six different exchange-correlation (XC) functionals.

DFT study of the adsorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin on pristine and Ni-doped boron nitride nanotubes.

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic to humans and the environment. Developing efficient methods to detect or remove these pollutants is particularly important and urgent. Boron nitride nanotubes (BNNTs) with low dimension and high surface-to-volume ratio might be one of promising materials for the adsorption of PCDD/Fs.