Density Functional Theory Study on the Mechanism of Nickel-Catalyzed 3,3-Dialkynylation of 2-Aryl Acrylamides Via Double Vinylic C-H Bond Activation.

The mechanisms of Ni-catalyzed 3,3-dialkynylation of 2-aryl acrylamide have been investigated by using density functional theory calculations. The result shows that this reaction includes double alkynylation, which involves sequential key steps of vinylic C-H bond activation, successive oxidative addition, and reductive elimination, with the second C-H bond activation being the rate-determining step. C-H and N-H bond activation occurs via the concerted metalation-deprotonation mechanism. The calculations show that no transition state exists in the first reductive elimination process, and a negative free energy barrier in the second reductive elimination process though a transition state is identified, indicating that the nickel-catalyzed vinylic C(sp2)-C(sp) bond formation does not require activation energy. Z-E isomerization is the prerequisite for the second alkynylation. In addition, our spin-flip TDDFT (SF-TDDFT) computational result discloses that the actual process of Z-E isomerization occurs on the potential energy surface of the first excited singlet state S1.

Density Functional Theory Study of the Mechanism of Ni-Catalyzed Carboxylation of Aryl C(sp2)-S Bonds with CO2: Computational Evidence for the Multifaceted Role of Additive Zn.

The mechanism of Ni-catalyzed carboxylation of aryl C(sp2)-S bonds with CO2 was studied for the first time by density functional theory calculations. We first proposed another possible reaction pathway in which CO2 insertion occurs prior to reduction. Then, we performed calculations on all proposed reaction pathways, and our calculation results show that the pathway in which reduction occurs prior to CO2 insertion is the favored pathway for this reaction. Additionally, our calculations disclose that additive Zn0 acts in multifaceted roles. (1) Zn0 acts as a reductant to reduce the NiI and NiII intermediates. (2) The simultaneously formed ZnIIBr2 can undergo transmetalation with NiI or NiII intermediates to produce an aryl reservoir by forming arylzinc species. (3) ZnIIBr2 can also coordinate to the CO2 to lower the energy barrier of the CO2 insertion step. Moreover, the calculation results suggest that CO2 insertion is the rate-determining step of the reaction, and CO2 is easier to insert into the NiI-Ph bond rather than into the NiII-Ph bond. These calculation results can improve our understanding of the mechanism of the carboxylation process and the multifaceted roles of metal additive Zn0 and provide theoretical guidance for improving the carboxylation reaction.

DFT Study on Mechanism of Ni-Al Bimetallic-Catalyzed C-H Cyclization to Construct Tricyclic Imidazoles: Roles of NHC Ligand and AlMe3.

The mechanism of the Ni-Al bimetallic-catalyzed C-H cyclization to construct tricyclic imidazoles is investigated using density functional theory calculations. The calculation result shows that the reaction mechanism involves sequential steps of substrate coordination, ligand-to-ligand hydrogen transfer (LLHT), and C-C reductive elimination to produce the final product tricyclic imidazole. The LLHT step is calculated to be the rate-determining step. The oxidative addition of the benzimidazole C-H bond to the Ni center and the insertion of the alkene into the Ni-H bond occur concertedly in the LLHT step. The effects of N-heterocyclic carbene (NHC) ligands and AlMe3 on the reactivity and regioselectivity were also analyzed. These calculation results shed light on some ambiguous suggestions from experiments.

DFT Study on the Mechanism of the Palladium-Catalyzed [3 + 2] Annulation of Aromatic Amides with Maleimides via Benzylic and meta-C-H Bond Activation: Role of the External Ligand Ac-Gly-OH.

The mechanism of the Ac-Gly-OH-assisted palladium-catalyzed [3 + 2] annulation of aromatic amides with maleimides is investigated using density functional theory calculations. The results show that the reaction undergoes the sequential steps of N-H bond deprotonation, first benzylic C-H bond activation, maleimide insertion, second meta-C-H bond activation, reductive elimination, and oxidation. The external ligand Ac-Gly-OH acts as the internal base for hydrogen abstraction in the first benzylic C-H bond activation. The maleimide insertion step is found to be the rate-determining step. Based on the nearly same energetic span of the two pathways to generate the enantio products, the computational results are consistent with the experimental observation that the terminal [3 + 2] annulation products are racemic when using an achiral ligand. These calculation results disclose the detailed reaction mechanism and shed light on some experimental ambiguities.

Computational Study of Iron-Catalyzed Intramolecular [2 + 2] Cycloaddition and Cycloisomerization of Enyne Acetates: Mechanism and Selectivity.

The mechanism of iron-catalyzed intramolecular [2 + 2] cycloaddition and cycloisomerization of enyne acetates has been investigated with DFT computations. Both mechanisms start the catalytic cycle from the stepwise 1,2-acyloxy migration to afford the iron carbene. The [2 + 2] cycloaddition mechanism involves subsequent key steps of [2 + 2] cycloaddition, 1,2-acyloxy migration, and reductive elimination to generate the azabicyclo [3.2.0] heptane product, with the reductive elimination being the rate-determining step. The cycloisomerization mechanism involves subsequent key steps of [2 + 2] cycloaddition, stepwise 1,4-acyloxy migration to produce the allenylpyrrolidine product, with the 1,4-acyloxy migration being the rate-determining step. Reaction potential energy surfaces for two model substrates that have or do not have alkene-terminal substituents have been investigated and the origins of the selectivities have been disclosed. Moreover, energy profiles with three possible spin states (SFe = 0, 1, 2) have been considered. The reaction is suggested to occur mainly on the singlet potential energy surface with a few spin crossovers between singlet and triplet states involved, which indicates that this reaction should have two-state reactivity (TSR).

Molecular Electrostatic Potential: A New Tool to Predict the Lithiation Process of Organic Battery Materials.

This work is pioneering to introduce molecular electrostatic potential (MESP) to investigate the interaction between lithium ions and organic electrode molecules. The electrostatic potential on the van der Waals surface of the electrode molecule is calculated, and then the coordinates and relative values of the local minima of MESP can be correlated to the Li binding sites and sequence on an organic small molecule, respectively. This suggests a gradual lithiation process. Similar calculations are extended to polymers and even organic crystals. The operation process of MESP for these systems is explained in detail. Through providing accurate and visualizable lithium binding sites, MESP can give precise prediction of the lithiated structures and reaction mechanism of organic electrode materials. It will become a new theoretical tool for determining the feasibility of organic electrode materials for alkali metal ion batteries.

The structure-electrochemical property relationship of quinone electrodes for lithium-ion batteries.

Quinones are promising electrode materials for lithium-ion batteries (LIBs), but their structure-electrochemical property relationship remains unclear. The aim of this study is to unravel the structural influence on the electrochemical properties of different quinones in LIBs. Through density functional theory calculations, redox potentials of 20 parent quinone isomers were examined, which revealed an increasing order of redox potentials as para-quinones < discrete-quinones < ortho-quinones. Two new methods were introduced to calculate and design organic electrode materials rationally. One is the vertical electron affinity in consideration of solvation effect, which was used to estimate the number of electron accommodation for quinones during lithiation. The other is a new index denoted as ΔA2Li used in para- and ortho-quinones, which was introduced to reveal the relationship between aromaticity and redox potential, establishing the theoretical basis for the design of analogous high-voltage organic electrode materials of LIBs.

Porphyrin-Based Symmetric Redox-Flow Batteries towards Cold-Climate Energy Storage.

Electrochemical energy storage with redox-flow batteries (RFBs) under subzero temperature is of great significance for the use of renewable energy in cold regions. However, RFBs are generally used above 10 °C. Herein we present non-aqueous organic RFBs based on 5,10,15,20-tetraphenylporphyrin (H2 TPP) as a bipolar redox-active material (anode: [H2 TPP]2- /H2 TPP, cathode: H2 TPP/[H2 TPP]2+ ) and a Y-zeolite-poly(vinylidene fluoride) (Y-PVDF) ion-selective membrane with high ionic conductivity as a separator. The constructed RFBs exhibit a high volumetric capacity of 8.72 Ah L-1 with a high voltage of 2.83 V and excellent cycling stability (capacity retention exceeding 99.98 % per cycle) in the temperature range between 20 and -40 °C. Our study highlights principles for the design of RFBs that operate at low temperatures, thus offering a promising approach to electrochemical energy storage under cold-climate conditions.

Rh(III)-Catalyzed Cascade Oxidative Annulation of Benzoylacetonitrile with Alkynes: Computational Study of Mechanism, Reactivity, and Regioselectivity.

The mechanism of the rhodium-catalyzed cascade oxidative annulation of benzoylacetonitrile with alkynes is investigated using density functional theory calculations. The result shows that the reaction undergoes a stepwise annulation process, wherein the 1-naphthol acts as an intermediate. The first-step annulation involves the sp(3) C-H bond cleavage, sp(2) C-H bond cleavage, alkyne insertion into the Rh-C(sp(2)) bond, ketone enolization, and reductive elimination to produce the 1-naphthol intermediate. The second-step annulation involves the O-H cleavage, sp(2) C-H bond cleavage, alkyne insertion into the Rh-C(sp(2)) bond, and C-O reductive elimination to generate the final product naphtho[1,8-bc]-pyran. The sp(3) C-H bond cleavage rather than the sp(2) C-H bond cleavage is found to be the rate-determining step of the catalytic cycle. The ketone enolization should occur before the reductive elimination. The substituent effects on the reactivities and regioselectivities of reactions are also analyzed. These calculation results shed light on some ambiguous suggestions from experiments.

From the molecular behaviors of fullerene derivatives C50X2 (X = H, F, Cl, Br, OH) to the general parallels among isostructural derivatives of fullerenes and carbon nanotubes.

A systematic investigation of all possible isomers of fullerene derivatives C50X2 (X = H, F, Cl, Br, OH) has been performed using the semiempirical AM1 method. The equilibrium geometrical structures, heats of formation, HOMO-LUMO energy gaps, ionization potentials, electronic affinities, strain and aromaticity have been studied. The results indicate that the selection rule for two groups adding to fullerene C50 is independent of the type of functional group. The isomer-78, which corresponds to a 1,4-addition at the six-membered ring located on the equator, is the most stable isomer for C50X2 (X = H, F, Cl, Br, OH). The driving force governing the stabilities of the presently studied C50X2 isomers is the strain inherent in the C50 cage. The contribution of the conjugation effect to the stabilization is not able to compete with that of the strain. The more stable C50X2 isomers have larger ionization potentials and smaller electronic affinities compared with C50, which suggests that it is more difficult to oxidize and reduce C50X2 than to oxidize and reduce C50. Energies as well as HOMO-LUMO gaps of isostructural C50X2 (X = H, F, Cl, Br, OH) isomers are almost parallel, i.e., energy differences between isostructural isomers of any two kinds of C50X2 derivatives are constant. This phenomenon can be called H/F/Cl/Br/OH parallels, which may result from the same degree of perturbation for addition of different functional groups to the structure of the parent carbon cage. H/F parallels are generalized characteristics among not only isostructural isomers of fullerenes but also isostructural isomers of carbon nanotubes. Furthermore, it is predictable that general H/F/Cl/Br/OH... parallels may exist among various derivatives of other fullerenes and carbon nanotubes.

Theoretical studies of the substitution patterns of boron-nitrogen (BN) fullerenes: from C50 up to C20B15N15 CBN ball.

Study on the patterns of successive BN pair substitution in C50 fullerene and the chemical and electronic properties of these substitutionally doped heterofullerenes has been carried out with semiempirical (AM1 and MNDO) and density functional (B3LYP/3-21G) theories. The BN units prefer to stay together following "single bond", "hexagon filling", and "continuity and equatorial belt" rules. The driving force governing the stabilities of these BN-doped fullerenes is the strain of the cage. Compared with C50, the redox activity of C50-2x(BN)x (x = 1-15) isomers decreases and becomes weaker by increasing the number of BN units, while the aromaticity of the C50-2x(BN)x derivatives decreases and is independent of the number of BN units but related to the substitution positions. The main infrared absorptions are similar for all the C50-2x(BN)x isomers and the infrared spectrum becomes simpler and stronger with increasing the number of BN groups.