Density Functional Theory Results Research Articles

Experimental and DFT study on titanium-based half-sandwich metallocene catalysts and their application for production of 1-hexene from ethylene

• The Ti metallocene catalysis guides selectively the trimerization from ethylene to 1-hexene. • Synthesis of [Ind-C(R)-Phenyl]TiCl 3 catalysts based on indenyl with various types of bridges (R) bearing an indenyl ring. • Selective catalysts for ethylene trimerization to 1-hexene using mild conditions. • Reaction mechanism and selectivity described by DFT calculations. • The highest catalytic activity with the catalyst with a cyclohexane middle bridge. Different types of [Ind-C(R)-Phenyl]TiCl 3 catalysts based on pendant arene containing indenyl (Ind) ligand bearing various types of bridges (R= cyclo ‐C 5 H 10 (C1), (CH 3 ) 2 (C2), 4- t Bu- cyclo ‐C 5 H 9 (C3), and cyclo ‐C 6 H 12 (C4)) have been synthesized, and used in the ethylene trimerization to 1-hexene in the presence of methyl aluminoxane (MAO) as co-catalyst. The reaction conditions were first optimized in C2 catalyst case, where the highest 1-hexene product was achieved at the catalyst concentration, temperature and ethylene pressure of 1.5 × 10 −3 M, 40 °C, and 8 bar, respectively. During this optimization and under specific reaction conditions, a switching behavior from ethylene trimerization to polymerization was also detected, as an undesired reaction. At the optimized conditions, synthesized catalysts showed the following trend toward both 1-hexene yield and selectivity: C1>C2>C3>C4. Then, to shed light on the possible reaction mechanisms and to confirm the activity trend obtained in experimental section, density functional theory (DFT) calculations were employed. In this line, obtained results for activity trend in the simulation studies fit well with the experiments. According to both experimental and DFT results, the highest catalytic activity was observed in the presence of the catalyst with a cyclohexane middle bridge (C1).

Surfactant inhibition mechanisms of carbonate mineral dissolution in shale

Surfactants are common additives to hydraulic fracturing and enhanced oil recovery (EOR) fluids, and are under consideration for amendment to supercritical carbon dioxide for geological carbon sequestration (GCS). The effect of a common anionic surfactant, internal olefin sulfonate (IOS), on mineral dissolution from shale into brine was evaluated. When added to brine at concentrations exceeding the critical micelle concentration (94 mg/L), IOS inhibited carbonate mineral dissolution in an Eagle Ford shale, as well as dissolution of optical quality calcite (the dominant carbonate in the shale). Laser profilometry images provide spatial resolution across > 3 orders of magnitude, and indicate that IOS addition to brine both enhances the formation of new etch pits in calcite, and impedes their further growth. Time-of-flight secondary ion mass spectrometry surface profiles show for the first time that IOS preferentially adsorbs at calcite pit edges versus flat calcite surfaces (i.e., terraces). Surface pressure calculations, sulfur K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy results, and density functional theory (DFT) calculations support this observation; the DFT results indicate that the sulfonate head group of the IOS molecule binds strongly to the calcite step site as compared to the terrace site. The S K-edge NEXAFS results indicate that IOS adsorbed more to etched calcite surfaces compared to smooth calcite surfaces. Overall, the results indicate that weak adsorption on flat calcite surfaces (i.e., terraces) disrupts water structure and enhances mass transfer of dissolution, while strong adsorption on calcite pit edges displaces adsorbed water and inhibits further etch pit growth. This work provides the first direct evidence of preferential adsorption of IOS to etched calcite surfaces and links it to macroscopic dissolution kinetics. This work has implications for surfactant-containing fluids used in hydraulic fracturing, EOR and potentially GCS for subsurface injection into carbonate rich reservoirs.

Illustration of potential energy surface from DFT calculation along with fuzzy logic modelling for optimization of N-acetylglycine

In this communication, Fuzzy logic scheme is applied to optimize the energy of the N-acetylglycine molecule along with the support of density functional theoretical results.The structure is optimized with DFT/B3LYP-6-31G(d,p) basis set using Gaussian 09 program. Inorder to identify the functional groups present in the studied molecule, the vibrational frequencies have been computed with the help of Density Functional Theory (DFT) computations. The best two torsional angles D1(H2O1C4O3) and D2(H9N8C10O11) of N-acetylglycine molecule that gives the global minimum is chosen for the fuzzy logic input and the results are compared with DFT results. Finally we believe that the fuzzy logic scheme gives reliable facts about the optimization of the structure of N-acetylglycine molecule with minimum energy in the light of density functional theory.

Multiphase tin equation of state using density functional theory

We perform density functional theory (DFT) calculations of five solid phases and the liquid phase of tin. The calculations include cold curves of the five solid phases, phonon calculations in the quasiharmonic approximation over a range of volumes for each solid phase, and DFT-based molecular dynamics (DFT-MD) simulations of the liquid phase, including those of the melt curve using the $Z$ method. Using the DFT results, we construct a tabular multiphase sesame equation of state for tin, referred to as sesame 2162. Comparisons to experimental data are made and show a high level of agreement in isobaric data, isothermal data, shock data, and phase boundary measurements, including measurements of the melt curve. The 2162 EOS will be useful for hydrodynamics simulations and has been designed with an eye toward hydrodynamics simulations that incorporate materials strength models and allow for modeling of the kinetics of phase transitions.

Electrochemically Modeling a Nonelectrochemical System: Hydrogen Peroxide Direct Synthesis on Palladium Catalysts.

Nonelectrochemical hydrogen peroxide direct synthesis (HPDS) under ambient conditions is an environmentally benign and energy-efficient process that produces a green oxidizer, yet the reaction mechanism of HPDS is still controversial. Inspired by the recently suggested heterolytic mechanism that involves electron and proton transfer at Pd catalysts, we propose a new electrochemical density functional theory (DFT) model that combines the Butler-Volmer equation and constant-potential DFT with hybrid explicit-implicit solvent treatment. Application of this model to Pd surfaces showed that the heterolytic mechanism has a lower barrier for the protonation steps for H2O2 production than for the nonelectrochemical hydrogenation steps, leading to advantageous kinetics for H2O2 production over H2O production, while the conventionally accepted Langmuir-Hinshelwood mechanism fails to explain the experimental kinetics. This work resolves the unanswered discrepancies between previous experimental and DFT results, and we expect that these results will readily help the systematic development of improved catalysts for HPDS.

Development of ReaxFFSFOH Force Field for SF6‐H2O/O2 Hybrid System Based on Synergetic Optimization by CMA‐ES and MC Methodology

AbstractThe reactive force field (ReaxFF) based molecular dynamic (MD) simulation provides a new perspective for studying the microscopic decomposition mechanism of sulfur hexafluoride (SF6) under fault conditions. Since none of the published ReaxFF force fields contains proper interaction relationship between S, F, O and H elements, the development of ReaxFF parameters for SF6‐H2O/O2 hybrid system is urgently needed. In this work, a universal and efficient covariance matrix adaptation evolutionary strategy (CMA‐ES) and Monte‐Carlo FF (MCFF) synergetic (CMS) optimization strategy for ReaxFF parameter is proposed. The optimization results for two representative force fields (disulfide and silica) from literature show that under the same number of evaluations, the CMS optimization strategy significantly reduces the optimization error by 22.08 % (disulfide) and 10.3 % (silica) respectively. By applying CMS strategy, the ReaxFFSFOH force field for SF6‐H2O/O2 hybrid system is efficiently obtained. Through multi‐dimensional force field performance verification, we find that the bond length calculation error between ReaxFF and density functional theory (DFT) calculation results is mainly concentrated within ±0.05 Å, and the bond angle error is mostly within ±5°. In addition, the trends of relative energy changes during chemical reaction processes calculated by ReaxFF are basically consistent with the DFT results. This work lays a solid foundation for the in‐depth study of the microscopic influence mechanism of trace H2O and trace O2 in the decomposition process of SF6.

Uncertainty of exchange-correlation functionals in density functional theory calculations for lithium-based solid electrolytes on the case study of lithium phosphorus oxynitride.

Amorphous lithium phosphorus oxynitride (LIPON) has emerged as a promising solid electrolyte for all-solid-state thin-film lithium batteries. In this context, the use of theoretical modeling to characterize, understand, or screen material properties is becoming increasingly important to complement experimental analysis or elucidate features at atomistic level that are difficult to obtain through experimental studies. Density functional theory (DFT) is the method of choice for quantum mechanical material modeling at the atomistic scale. The current state of the art represents DFT values, such as the formation or migration energies relevant for bulk phase of materials, as absolute numbers. Estimating the accuracy or fluctuation range of the different density functionals is challenging. In order to investigate the thermodynamic and kinetic properties of LIPON by DFT, an approach to describe the fluctuation range caused by the choice of the exchange-correlation (XC) functional is developed. Three different model systems were chosen to characterize various structural features of amorphous LIPON, which are distinguished by the cross-linking of the POu N4-u -structural units. The uncertainty Ũ is introduced as a parameter describing the fluctuation range of energy values. The uncertainty approach does not determine the accuracy of DFT results, but rather a fluctuation range in the DFT results without the need for a reference value from a higher level of theory or experiment. The uncertainty was determined for both the thermodynamic Li-vacancy formation energies and the kinetic Li-vacancy migration energies in LIPON. We assume that the uncertainty approach can be applied to different material systems with different density functionals.

Investigation of Rosemary Active Ingredients as COVID-19 Inhibitors: Molecular Docking and DFT

Rosemary is an important type of the natural Lamiaceae plant family with several medicinal properties, rendering it as a prospective inhibitor for the new SARS-CoV-2 virus. Its SARS-CoV-2 inhibition properties has not yet been reported. In this study the inhibition efficacy of rosemary against SARS-CoV-2 has been demonstrated using molecular docking along with systematic density-functional-theory (DFT) calculations. The estimated DFT data have shown that the dipole moment of rosemary active ingredient was in the range of 4.29-1.68 with the highest value attained by the carnosic acid. The high dipole moment for the carnosic acid may indicate its appropriate binding affinity pose within a specific virus target receptor. Moreover, the structural complexity for the carnosic acid gave rise to its highest calculated polarizability of 225.5 Bohr3 compared to the rest of the rosemary ingredients. Remarkably, the carnosic acid active ingredient has the least energy gap between the frontier orbitals (highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)) of ~ 5.43 eV, with several hydrophilic sites for interactions, further enabling its binding with the virus receptors. Interestingly, and as anticipated from DFT results, molecular docking calculations showed that carnosic acid had the least binding energy (−6.9 kcal/mol) and, hence, can be regarded as a prospective inhibitor to SARS-CoV-2 main protease (Mpro). It binds to both Mpro catalytic dyads (Cys-145 and His-41) with hydrogen bond and π-interaction. This carnosic acid ligand binding quality was comparable to renowned SARS-CoV-2 drugs, hydroxychloroquine and favipiravir, having binding affinities of −6.1 and −5.1 kcal/mol, respectively.

Density functional theory study of the mechanical behavior of silicene and development of a Tersoff interatomic potential model tailored for elastic behavior

Silicene, a graphene-like 2D material made from Si atoms, has been fabricated and studied for its promising applications in micro/nanoelectronics. For the reliable function of silicene devices, it is important to investigate silicene’s mechanical properties. In this study, the authors conducted density functional theory (DFT) simulations of mechanical tests of silicene and investigated the elastic modulus and mechanical response such as structural transformation. In addition, the authors optimized the Tersoff potential parameters using a gradient-based minimization with a grid search method in hyperdimensional parameter space, to match the DFT calculation results in the elastic regime. With the new parameter set, the elastic moduli of silicene in the zigzag (ZZ) and armchair (AC) directions were computed with molecular statics (MS) simulations and compared with those of other Si interatomic potential models and DFT results. In addition, uniaxial tensile tests along the ZZ and AC directions were performed to examine how far the Tersoff model is transferable with our new parameter set to describe the nonlinear mechanical behavior of silicene. The results of uniaxial tensile tests suggest that the angle penalty function in the Tersoff model needs to be modified and that the stress–strain curve predicted with this modification shows improvement compared to the original function.

Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes.

The correlation consistent Composite Approach for transition metals (ccCA-TM) and density functional theory (DFT) computations have been applied to investigate the fluxional mechanisms of cyclooctatetraene tricarbonyl chromium ((COT)Cr(CO)3) and 1,3,5,7-tetramethylcyclooctatetraene tricarbonyl chromium, molybdenum, and tungsten ((TMCOT)M(CO)3 (M = Cr, Mo, and W)) complexes. The geometries of (COT)Cr(CO)3 were fully characterized with the PBEPBE, PBE0, B3LYP, and B97-1 functionals with various basis set/ECP combinations, while all investigated (TMCOT)M(CO)3 complexes were fully characterized with the PBEPBE, PBE0, and B3LYP methods. The energetics of the fluxional dynamics of (COT)Cr(CO)3 were examined using the correlation consistent Composite Approach for transition metals (ccCA-TM) to provide reliable energy benchmarks for corresponding DFT results. The PBE0/BS1 results are in semiquantitative agreement with the ccCA-TM results. Various transition states were identified for the fluxional processes of (COT)Cr(CO)3. The PBEPBE/BS1 energetics indicate that the 1,2-shift is the lowest energy fluxional process, while the B3LYP/BS1 energetics (where BS1 = H, C, O: 6-31G(d′); M: mod-LANL2DZ(f)-ECP) indicate the 1,3-shift having a lower electronic energy of activation than the 1,2-shift by 2.9 kcal mol−1. Notably, PBE0/BS1 describes the (CO)3 rotation to be the lowest energy process, followed by the 1,3-shift. Six transition states have been identified in the fluxional processes of each of the (TMCOT)M(CO)3 complexes (except for (TMCOT)W(CO)3), two of which are 1,2-shift transition states. The lowest-energy fluxional process of each (TMCOT)M(CO)3 complex (computed with the PBE0 functional) has a ΔG‡ of 12.6, 12.8, and 13.2 kcal mol−1 for Cr, Mo, and W complexes, respectively. Good agreement was observed between the experimental and computed 1H-NMR and 13C-NMR chemical shifts for (TMCOT)Cr(CO)3 and (TMCOT)Mo(CO)3 at three different temperature regimes, with coalescence of chemically equivalent groups at higher temperatures.

Nanotechnology-based approaches for targeting and delivery of drugs via Hexakis (m-PE) macrocycles

Hexakis (m-phenylene ethynylene) (m-PE) macrocycles, with aromatic backbones and multiple hydrogen-bonding side chains, had a very high propensity to self-assemble via H-bond and π–π stacking interactions to form nanotubular structures with defined inner pores. Such stacking of rigid macrocycles is leading to novel applications that enable the researchers to explored mass transport in the sub-nanometer scale. Herein, we performed density functional theory (DFT) calculations to examine the drug delivery performance of the hexakis dimer as a novel carrier for doxorubicin (DOX) agent in the chloroform and water solvents. Based on the DFT results, it is found that the adsorption of DOX on the carrier surface is typically physisorption with the adsorption strength values of − 115.14 and − 83.37 kJ/mol in outside and inside complexes, respectively, and so that the essence of the drug remains intact. The negative values of the binding energies for all complexes indicate the stability of the drug molecule inside and outside the carrier's cavities. The energy decomposition analysis (EDA) has also been performed and shown that the dispersion interaction has an essential role in stabilizing the drug-hexakis dimer complexes. To further explore the electronic properties of dox, the partial density of states (PDOS and TDOS) are calculated. The atom in molecules (AIM) and Becke surface (BS) methods are also analyzed to provide an inside view of the nature and strength of the H-bonding interactions in complexes. The obtained results indicate that in all studied complexes, H-bond formation is the driving force in the stabilization of these structures, and also chloroform solvent is more favorable than the water solution. Overall, our findings offer insightful information on the efficient utilization of hexakis dimer as drug delivery systems to deliver anti-cancer drugs.

In data science we trust: Machine learning for stable halide perovskites

The exploration of the compositional space of halide perovskites is prohibitively costly using traditional experimental research strategies. Sun and colleagues demonstrated a physics-informed, machine-learning-guided, experimental approach that overturns this limitation enabling a rapid and efficient maximization of stability in mixed-cation perovskites.

Examinations directed to characterization within the framework of spectroscopic and DFT approach on the structural isomer of the pyridine substituted thiazole

In the present paper, we reported the synthesis of two structural isomers of pyridine-substituted thiazole having heterocyclic moieties, characterized by XRD, FT-IR, NMR, UV-Vis and fluorescence techniques. Their molecular geometries and presence of hydrogen bond interactions were determined with single-crystal X-ray diffraction (XRD) analysis. The process steps of analyses performed with the theoretical approach were carried out with density functional theory (DFT), B3LYP functional and 6-311G(d,p) basis set. The parameters of molecular geometry, spectral vibrational modes base on potential energy distribution (PED) and 1H and 13C-NMR chemical shifts for the structures were evaluated comparatively with DFT results. To determine photophysical properties, absorption bands with the time-dependent DFT (TD-DFT) approach and spectral emission bands were examined. Frontier molecular orbitals (FMOs), global and local reactivity descriptors, atomic charge distributions based on Mulliken and Natural Population analysis (MPA and NPA) were utilized to specify the reactivity properties of the structures. Further, nonlinear optical (NLO) properties and some thermodynamic parameters were investigated at the same theoretical level. The results of these analyses show that most of the spectral parameters examined are sensitive to the position of the substituent and the pyridine substitution 4-position to thiazole structure exhibit chemically more reactive a profile than at 2-position.

Molecular structure aspects and molecular reactivity of some triazole derivatives for corrosion inhibition of aluminum in 1 M HCl solution

The corrosion inhibition of three triazole derivatives; p-tolyl-1H-1,2,3-triazol-5-ol (Z1), 4-Chlorophenyl-1H-1, 2, 3-triazol-5-ol (Z2) and Methyl-4-(5‑hydroxy-1H-1, 2, 3-triazol-1-yl) benzoate (Z3) towards aluminum metal in 1.0 M HCl have been investigated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), B3LYP Density Functional Theory (DFT) and adsorption annealing simulations. The electrochemical findings exhibit an inhibition efficiency increase in the order: Z3 > Z2 > Z1 with a maximum inhibition efficiency (74.7%) obtained at 500 ppm from Z3. Both anodic (βa) and cathodic (βc) Tafel constants was significantly affected by adding inhibitors to the corrosion medium proposing a mixed type nature. The adsorption of the inhibitors on the metal surface was found to be a spontaneous process and obeyed Langmuir isotherm. The conformational scan along with annealing adsorption simulations showed a dihedral angle between the triazole ring and the phenyl ring of only 30° which promotes optimal surface coverage. Global reactivity descriptors, Fukui indices, atomic charges and NBO analysis showed that the priority of charge reallocation form inhibitor MOs to the metal surface is easier in the order: Z3 > Z2 >Z1 which reveal good agreement to the electrochemical measurements. Based on DFT results, an inhibition mechanism was proposed.

Phosphonate Chelators for Medicinal Metal Ions.

A family of phosphonate-bearing chelators was synthesized to study their potential in metal-based (radio)pharmaceuticals. Three ligands (H6phospa, H6dipedpa, H6eppy; structures illustrated in manuscript) were fully characterized, including X-ray crystallographic structures of H6phospa and H6dipedpa. NMR spectroscopy techniques were used to confirm the complexation of each ligand with selected trivalent metal ions. These methods were particularly useful in discerning structural information for Sc3+ and La3+ complexes. Solution studies were conducted to evaluate the complex stability of 15 metal complexes. As a general trend, H6phospa was noted to form the most stable complexes, and H6eppy associated with the least stable complexes. Moreover, In3+ complexes were determined to be the most stable, and complexes with La3+ were the least stable, across all metals. Density functional theory (DFT) was employed to calculate structures of H6phospa and H6dipedpa complexes with La3+ and Sc3+. A comparison of experimental 1H NMR spectra with calculated 1H NMR spectra using DFT-optimized structures was used as a method of structure validation. It was noted that theoretical NMR spectra were very sensitive to a number of variables, such as ligand configuration, protonation state, and the number/orientation of explicit water molecules. In general, the inclusion of an explicit second shell of water molecules qualitatively improved the agreement between theoretical and experimental NMR spectra versus a polarizable continuum solvent model alone. Formation constants were also calculated from DFT results using potential-energy optimized structures. Strong dependence of molecular free energies on explicit water molecule number, water molecule configuration, and protonation state was observed, highlighting the need for dynamic data in accurate first-principles calculations of metal-ligand stability constants.

Selectivity and competition between N–H and C–H bond activation using an organoplatinum (II) complex

2‐(2′‐Pyridyl)benzimidazole (Hpbz), containing both C–H and N–H bonds available for activation, has been investigated to elucidate which bond is activated upon coordination to the Pt(II) precursor complex (PtMe2(DMSO)2), 1. On the basis of density functional theory (DFT), Hpbz is predicted to react with 1 through N–H bond activation of the benzimidazole ring in preference to C–H bond activation of the pyridine ring. The reasons for this difference in selectivity are discussed based on the energy barrier needed for N–H versus C–H bond activation. The DFT results are in agreement with experimental findings in which reaction of Hpbz with 1 at room temperature leads to N–H bond activation to give (PtMe(pbz‐κ2‐N,N)(DMSO)), 2. The kinetic and mechanistic study of the reaction between Hpbz and 1 shows that the reaction occurs through substitution of one DMSO by the nitrogen atom of pyridine ring of Hpbz to give (PtMe2(Hpbz‐κ1N)(DMSO)), followed by N–H activation and release of methane to form 2.

Enhanced thermoelectric performance of Bi0.5Sb1.5Te3 via Ni-doping: A Shift of peak ZT at elevated temperature via suppressing intrinsic excitation

Bi2Te3-based thermoelectric (TE) materials have been demonstrated to be a potential candidate for mainly thermoelectric cooling/refrigeration applications. However, minority charge carriers excitation at high temperature reduces thermopower which restricts these materials for the use in power generation. In present work, substitution of Ni on Sb site in Bi0.5Sb1.5-xNixTe3 (x = 0, 0.01, 0.04 and 0.08) actuates the system to supress the intrinsic excitation leading to shift in highest ZT to higher temperature regime. The Density functional theory (DFT) calculations and experimental results reveal that Ni in Bi0.5Sb1.5Te3 provides the extra holes and slightly reduces the band gap Eg which enhances the σ of Ni-doped Bi0.5Sb1.5-xNixTe3 samples and α at elevated temperature. Moreover, Ni-doping in Bi0.5Sb1.5Te3 also reduces κL which is attributed to the phonon scattering due to mass fluctuations and microstructural features such as grain boundary and strain field domain observed from HRTEM investigation. These favourable condition leads to maximum ZT∼1.38 at 433K for Bi0.5Sb1.46Ni0.04Te3 and ZTavg ∼1.1 between 300K and 503K. Interestingly the calculated theoretical TE conversion device efficiency η of Bi0.5Sb1.46Ni0.04Te3 (η∼5.5%) was achieved to be nearly twice than the efficiency of matrix Bi0.5Sb1.5Te3 (η∼3%). Experimental electronic transport is well corroborated with theoretically estimated DFT results.

Applicability of DFT functionals for evaluating the first hyperpolarizability of phenol blue in solution.

The first electronic hyperpolarizability (β) of phenol blue (PB) in several solvents in a wide range of dielectric constants is investigated using the density functional theory (DFT). The reliability of various exchange-correlation functionals is assessed by a comparison to reference Møller-Plesset second-order perturbation theory (MP2) calculations. The equilibrium geometry of PB in each solvent is obtained by using the average solvent electrostatic configuration/free energy gradient method, which performs optimizations on the free energy hyper-surface by employing iteratively the sequential quantum mechanics/molecular mechanics methodology. The dependence of β on the bond length alternation (BLA) coordinate is rationalized by means of the two-level model. Within the employed exchange-correlation functionals, the LC-BLYP functional shows the best performance for describing the static and dynamic MP2 results of β, which increases as the BLA diminishes, reaching a maximum in an intermediate value of BLA. The results also illustrate the role played by the difference between the ground- and excited-state dipole moments (Δμ) in determining the hyperpolarizability behavior in solution. Particularly, in the aqueous solution case, Δμ goes to around zero when BLA is near zero, leading to an abrupt decline in the β value. The DFT results of this study, therefore, indicate a clear relationship between the first hyperpolarizability and the BLA coordinate for the PB in solution, in agreement with experiment.

Переходный металл и неметаллический со-легирующий графен для электрокатализа реакции восстановления кислорода: исследование функциональной теории плотности

Proton exchange membrane fuel cells (PEMFCs) are vital energy-conversion devices in a hydrogen-fueled economic. In this study, we performed density functional theory (DFT) calculations to study 4e− oxygen reduction reaction process on transition metal embedded in single and double vacancies (SV and DV) in a graphene. We calculated bonding energy and adsorption energy on CoX3 (X = B, C, N, Si, P and S) and CoX4 (X = B, C, N, Si, P and S) embedded in graphene. Our DFT results indicate that formation of CoX3 is unfeasible and the formation of CoX4 is feasible. In addition, the crucial role of ligand atoms near embedded metal atoms is revealed via the molecular orbital theory. Then the Gibbs free energy of CoX4 are calculated and the CoN4, CoS4, and CoP4 are predicted to be active for catalyzing ORR, and these also show ligand atoms’ coordination effect for catalytic activity of central metal. Furthermore, we observed that they have identical rate-determining step (RDS). This work can provide some references for transition atoms catalytic doped in carbon materials.

Pd‐Catalyzed Regio‐ and Stereoselective sp3 C−H Arylation of Primary Aliphatic Amines: Mechanistic Studies and Synthetic Applications

AbstractThe Pd‐catalyzed γ‐position sp3−C−H arylation of primary amines bearing an aliphatic chain or cycloalkyl substituent and related mechanistic studies are disclosed. 3‐Bromo‐2‐hydroxybenzaldehyde plays a key role in γ‐position sp3−C−H arylation as a transient directing group (TDG) to assist the regio‐ and stereoselective C−H activation of a Pd catalyst, and the development of a tandem reaction to transform 1°‐amines into γ‐aryl‐substituted ketones demonstrates synthetic utility. Density functional theory (DFT)‐based calculations revealed the detailed reaction mechanism and the origins of the high selectivity (γ‐position and cis‐only). The X‐ray crystal structure of the isolated endo‐palladacycle intermediate supported the DFT results, and a kinetic isotope experiment confirmed the results of DFT calculations indicating that the C−H activation step via simultaneous palladation and deprotonation is rate‐determining.