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We have investigated the metal–ligand bond energies in C2H4–Pt(PH3)2and C60–Pt(PH3)2by means ofab initiocorrelated methods (MP2, MP4(SDQ), MP4, QCISD, CCSD and CCSD(T)) in conjunction with large basis sets. For De(C2H4–Pt(PH3)2), an accurate value of 17.2 kcal/mol is established at the CCSD(T) level of theory. Due to the size of the system, the bond energy for the Buckminsterfullerene system was explored in terms of a sequence of model systems of increasing size, providing a Deestimate of 28.2 kcal/mol at the ONIOM(CCSD(T)/C14H8:MP2/C60) level of theory. The performance of a range of high-end density functionals (with and without dispersion) is evaluated for these systems by comparison to the bestab initioresults. Among these, we find density functionals BLYP and B3LYP, augmented by Grimme’s D3 dispersion correction (to give the corresponding DFT-D methods), to provide good and consistent agreement with our best estimates. Next, DFT-optimised structures for C2H4–Pt(PPh3)2and C60–Pt(PPh3)2are presented for the first time. Ligand binding energies were computed for ethylene and C60using DFT-D, thus allowing the first computational estimate of the driving force in the ligand substitution reaction (η2-C2H4)Pt(PPh3)2+C60→ (η2-C60)Pt(PPh3)2+C2H4. [ABSTRACT FROM AUTHOR]

A DFT investigation of substitutional metallofullerenes MC 59 (M=Sc—Ni) shows that they are drop‐shaped, with the deviation from spherical structure depending on the size of the metal atom. The metal atomic radius, however, seems to be unimportant for the stability of the metallofullerenes. In general, the stability increases toward the right‐hand side of the transition series, commensurate with the higher electronegativities of the late transition metals. CrC 59 is calculated to be more stable than the metallofullerenes of manganese and iron, suggesting that future observation of CrC 59 may be anticipated. [ABSTRACT FROM AUTHOR]

Models of Cr(III)–silica were used to study C&bond;H activation in ethane by oxidative addition as a possible route to catalytic dehydrogenation. This mechanism involves a formal double oxidation of chromium and a minimum energy crossing point (MECP) was located on the seam between the quartet spin potential energy surface of Cr(III) and the doublet spin potential energy surface of Cr(V). Subsequent to the change of spin state, the C&bond;H activation path passes through a transition state on the doublet potential surface, leading to the formation of an ethylhydridochromium(V) complex. This complex represents only a shallow minimum on the potential energy surface and β-hydrogen transfer to complete the catalytic cycle must therefore take place in the extension of the C&bond;H activation step. The combination of a significant activation energy and a small pre-exponential factor in the rate constant makes C&bond;H activation by oxidative addition an unlikely mechanism for dehydrogenation in this system. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The influence of core–hole delocalization for x-ray photoelectron, x-ray absorption, and x-ray emission spectrum calculations is investigated in detail using approaches including response theory, transition-potential methods, and ground state schemes. The question of a localized/delocalized vacancy is relevant for systems with symmetrically equivalent atoms, as well as near-degeneracies that can distribute the core orbitals over several atoms. We show that the issues relating to core–hole delocalization are present for calculations considering explicit core–hole states, e.g., when using a core-excited or core-ionized reference state or for fractional occupation numbers. As electron correlation eventually alleviates the issues, but even when using coupled-cluster single-double and perturbative triple, there is a notable discrepancy between core-ionization energies obtained with localized and delocalized core–holes (0.5 eV for the carbon K-edge). Within density functional theory, the discrepancy correlates with the exchange interaction involving the core orbitals of the same spin symmetry as the delocalized core–hole. The use of a localized core–hole allows for a reasonably good inclusion of relaxation at a lower level of theory, whereas the proper symmetry solution involving a delocalized core–hole requires higher levels of theory to account for the correlation effects involved in orbital relaxation. For linear response methods, we further show that if x-ray absorption spectra are modeled by considering symmetry-unique sets of atoms, care has to be taken such that there are no delocalizations of the core orbitals, which would otherwise introduce shifts in absolute energies and relative features. [ABSTRACT FROM AUTHOR]

1,2,4-Triazoline-3,5-diones (TADs) are versatile reagents and have found widespread adoption in chemical science. Despite their remarkable reactivity toward a wide array of unsaturated hydrocarbons, the chemical reaction between TADs and alkynes has remained largely unexplored. Herein, we demonstrate that 1,1,1,3,3,3-hexafluoro-2-propanol facilitates the unusual [3+2] cycloaddition between 4-phenyl-1,2,4-triazoline-3,5-dione and alkynes, resulting in the formation of unprecedented mesoionic triazolones. Moreover, the structural properties of the resulting triazolone have been investigated by employing X-ray diffraction analysis and Density Functional Theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

We present a relativistic correction scheme to improve the accuracy of 1s core-level binding energies calculated from Green's function theory in the GW approximation, which does not add computational overhead. An element-specific corrective term is derived as the difference between the 1s eigenvalues obtained from the self-consistent solutions to the non- or scalar-relativistic Kohn–Sham equations and the four-component Dirac–Kohn–Sham equations for a free neutral atom. We examine the dependence of this corrective term on the molecular environment and the amount of exact exchange in hybrid exchange–correlation functionals. This corrective term is then added as a perturbation to the quasiparticle energies from partially self-consistent and single-shot GW calculations. We show that this element-specific relativistic correction, when applied to a previously reported benchmark set of 65 core-state excitations [D. Golze et al., J. Phys. Chem. Lett. 11, 1840–1847 (2020)], reduces the mean absolute error (MAE) with respect to the experiment from 0.55 eV to 0.30 eV and eliminates the species dependence of the MAE, which otherwise increases with the atomic number. The relativistic corrections also reduce the species dependence for the optimal amount of exact exchange in the hybrid functional used as a starting point for the single-shot G0W0 calculations. Our correction scheme can be transferred to other methods, which we demonstrate for the delta self-consistent field (ΔSCF) approach based on density functional theory. [ABSTRACT FROM AUTHOR]

On purpose, selective oligomerization of ethylene to its linear trimer and tetramer such as 1-hexene and 1-octene has assumed significant commercial interest. Catalytic systems based on chromium and titanium have shown remarkable selectivity and productivity for the tri and tetramerization of ethylene to 1-hexene or 1-octene. Chromium-based catalysts are the most selective and active and show the highest structural diversity. This article discusses the most recent mechanistic approaches regarding active catalytic species that determine the selectivity to either hexene-1 or octene-1 and reaction parameters that control selectivity of byproducts. Isotopic labeling protocols, in-situ spectroscopic investigations and DFT studies on selected chromium-based catalyst systems are reviewed. [ABSTRACT FROM AUTHOR]

High resolution X-ray photoelectron spectra of a series of substituted pyridines (pyridine, 2-fluoropyridine, and 2,6-difluoropyridine) have been recorded and rationalized by means of a quantum mechanical approach based on the density functional theory including vibronic effects at the Franck-Condon level. The significant chemical shifts of the C1s binding energies induced by fluorine atoms are reproduced quantitatively by our computational model, as well as the vibrational fine structure and the band shapes. Nonsymmetric normal modes play an important role due to the core-hole localization in the presence of equivalent carbon atoms in pyridine and 2,6-difluoropyridine. [ABSTRACT FROM AUTHOR]

A frontier challenge in single‐atom (SA) catalysis is the design of fully inorganic sites capable of emulating the high reaction selectivity traditionally exclusive of organometallic counterparts in homogeneous catalysis. Modulating the direct coordination environment in SA sites, via the exploitation of the oxide support's surface chemistry, stands as a powerful albeit underexplored strategy. We report that isolated Rh atoms stabilized on oxygen‐defective SnO2 uniquely unite excellent TOF with essentially full selectivity in the gas‐phase hydroformylation of ethylene, inhibiting the thermodynamically favored olefin hydrogenation. Density Functional Theory calculations and surface characterization suggest that substantial depletion of the catalyst surface in lattice oxygen, energetically facile on SnO2, is key to unlock a high coordination pliability at the mononuclear Rh centers, leading to an exceptional performance which is on par with that of molecular catalysts in liquid media. [ABSTRACT FROM AUTHOR]

Although computational contributions to the understanding of organometallic homogeneous catalysts have become fairly routine, a step‐change in the application of computational methods would be to achieve efficient, robust, and reliable prediction of the outcome of catalytic transformations. While we concur that there have been a number of recent promising advances in the interactions between computational and experimental mechanistic studies, the mapping of reactivity space remains incomplete and large‐scale studies have to make limiting assumptions which restrict their transferability. Close synergies between characterization and analysis techniques which are integrated with computational data, along with data capture, curation, and exploitation, are vital and develop our understanding of all aspects of the catalytic pathways (including activation and deactivation) and allow the continual refinement of mechanistic understanding, challenged by testing predictions experimentally. Here we review recent examples to formulate a protocol for such interactions. This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsStructure and Mechanism > Reaction Mechanisms and CatalysisData Science > Artificial Intelligence/Machine LearningElectronic Structure Theory > Density Functional Theory [ABSTRACT FROM AUTHOR]

The electronic structure of short-chain thiophenes (thiophene, 2,2'2'-bithiophene, and 2,2':5',2"-terthiophene) in the gas phase has been investigated by combining the outcomes of Near-Edge X-ray-Absorption Fine-Structure (NEXAFS) and X-ray Photoemission Spectroscopy (XPS) at the C K-edge with those of density functional theory (DFT) calculations. The calculated NEXAFS spectra provide a comprehensive description of the main experimental features and allow their attribution. The evolution of the C1s NEXAFS spectral features is analyzed as a function of the number of thiophene rings; a tendency to stabilization for increasing chain length is found. The computation of the binding energy allows to assign the experimental XPS peaks to the different carbon sites on the basis of both the inductive effects generated by the presence of the S atom as well as of the differential aromaticity effects. [ABSTRACT FROM AUTHOR]

Density functional theory calculations are often used to interpret experimental shifts in core level binding energies. Calculations based on gradient-corrected (GC) exchange-correlation functionals are known to reproduce measured core level shifts (CLS) of isolated molecules and metal surfaces with reasonable accuracy. In the present study, we discuss a series of examples where the shifts calculated within a GC-functional significantly deviate from the experimental values, namely the CLS of C 1s in ethyl trifluoroacetate, Pd 3d in PdO and the O 1s shift for CO adsorbed on PdO(101). The deviations are traced to effects of the electronic self-interaction error with GC-functionals and substantially better agreements between calculated and measured CLS are obtained when a fraction of exact exchange is used in the exchange-correlation functional. © 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [ABSTRACT FROM AUTHOR]

Investigation of the decomposition products of SF6–CO2 gas mixture, which is a promising binary gas mixture with dilute SF6 content to be used in gas-insulated systems in power electrical systems, is very important in terms of the sustainability of operating conditions, environmental and human health. This study determines the decomposition products of the SF6–CO2 gas mixture in the presence of H2O, depending on the reaction paths by the B3LYP method at 6-311 + G(d,p) level set employing the density functional theory method. The decomposition products obtained by this method have been confirmed by the findings of experimental studies in the literature. Decomposition pathways of SF6 + CO2 mixture in the absence and presence of H2O are constructed in order to analyze relative energy changes of the decomposed by-products to select the most probable ones. [ABSTRACT FROM AUTHOR]

Recently, we reported the first VOx/SiO2 ethylene polymerization catalyst for making Cl-free UHMWPE, and found the dominant promotion effects of Al-/Ti-/Zr-modifications over this catalyst system (Macromol. Chem. Phys. 2017, 218, 1600443). In this work, density functional theory is applied to investigate the underlying mechanism of this remarkable promotion effect of Al-/Ti-/Zr-modifications on a molecular and atomic level. The cluster model with V(III) is found to be the most possible active site due to its lowest overall energy barrier for monomer insertion, though the process of C2H4 coordination and the subsequent formation of transition state are most energy favored for V(II) species. By modifying one of or both V-O-Si in the active model with V-O-M (M = Al, Ti, or Zr), the energy barrier for the binding of the upcoming C2H4 gets lower (particularly for Al- and Zr-modified catalysts), and the transition state also becomes more stable. Generally, the insertion process of C2H4 gets easier after support Al-/Ti-/Zr-modifications. This dominant promotion effect is partially ascribed to the more enriched positive charge distribution on or nearby the V center, and the narrower energy gap between the LUMO of model catalysts and the HOMO of C2H4 for these modified catalysts also contributes much. In addition, the decreased steric hindrance around the V center should be taken into account for the modified models as well. Furthermore, the Brønsted acidity of the catalysts is investigated by introducing a pendent hydroxyl group to the model catalysts, which has a close contact with the V center. Similar promotion effect of support modification by Al, Ti, and Zr could still be observed. [ABSTRACT FROM AUTHOR]

A variety of density functionals and Gaussian basis sets has been studied for performance in calculations of core-electron binding energies of the carbon, nitrogen, and oxygen nuclei in the gaseous amino acids glycine, alanine, proline, threonine, and methionine. The main goal of this study is the identification of methods that will be sufficiently accurate and efficient to be used for analysis of experimental X-ray photoelectron spectra of amino acids, large polypeptides, and DNA nucleosides in various environments. The various methods studied are evaluated based on consideration of their performance for calculation of relative conformer energies, core-electron binding energies, and chemical shifts of the binding energies, using common popular density functionals with small basis sets. [ABSTRACT FROM AUTHOR]

The coordination mode of triphenylphosphine to rhodium is considered to be important for the outcome of hydroformylation catalysis. The difference in reactivity between mono- and bis-ligated rhodium species has not been investigated systematically, mostly because it is impossible to obtain pure mono-ligated rhodium under hydroformylation conditions. Therefore, we performed detailed computational studies to get an insight into the effect of the coordination of triphenylphosphine to rhodium on hydroformylation catalysis. The DFT-calculated catalytic pathway of the monophosphine-based catalyst shows a lower free energy barrier (24.5 kcal mol−1) compared to the pathway of the bisphosphine catalyst (28.9 kcal mol−1). This confirms that monophosphine catalysts have an intrinsically higher activity than bisphosphine catalysts and indicates that the rate enhancement seen with the tetraphenylporphyrin-based catalyst reported by our group previously is at least partly due to the monocoordination enforced by this encapsulating ligand. [ABSTRACT FROM AUTHOR]

Carbon-supported MgO materials are excellent and sustainable catalysts for the synthesis of N-containing heterocyclic compounds by the Friedländer condensation under mild, solvent-free conditions. The results reported herein indicate that MgO is the most active catalytic species that accelerates the reaction compared with the catalytic behavior observed for the carbon material Norit RX3. On the basis of DFT calculations, a reaction mechanism that involves dual activation of the reacting structures by the catalyst is proposed. [ABSTRACT FROM AUTHOR]

Density functional theory, coupled-cluster theory, and transition state theory are used to build a computational model of the kinetics of phosphine-free cobalt-catalyzed hydroformylation and hydrogenation of alkenes. The model provides very good agreement with experiment, and enables the factors that determine the selectivity and rate of catalysis to be determined. The turnover rate is mainly determined by the alkene coordination step. [ABSTRACT FROM AUTHOR]

A number of density functionals are benchmarked for calculation of 1s core electron binding energies for carbon, nitrogen, and oxygen nuclei in glycine, and for comparison in the first-row hydrides methane, ammonia, and water. The goal is to establish methods having potential to aid the analysis of experimental X-ray photoelectron spectra on compounds such as amino acids, DNA nucleosides, and large polypeptides in various environments. Several promising density functionals are identified that can reproduce experimental results within 0.2 eV on average for the absolute binding energies and also for the intramolecular and intermolecular shifts in the studied molecules. [ABSTRACT FROM AUTHOR]

The performance of density functional theory in reproducing some of the main interactions occurring in MgCl2-supported Ziegler-Natta catalytic systems is assessed. Eight model systems, representatives of key interactions occurring in Ziegler-Natta catalysts, are selected. Fifteen density functionals are tested in combination with two different basis sets, namely, TZVP and cc-pVTZ. As a general result, we found that the best performances are achieved by the PBEh1PBE hybrid generalized gradient approximation (GGA) functional, but also the cheaper PBEh GGA functional gives rather good results. The failure of the popular B3LYP and BP86 functionals is noticeable. [ABSTRACT FROM AUTHOR]

The ability of the Et2Al–R co-catalyst series [with R = Et, Cl, O–Me, O-iPr, NH–Me, S–Me, and S–iPr] to alkylate titanum chloride has been evaluated at the B3LYP/6-31G* level of approximation. The impact of dimerization and complexation by Lewis bases on their alkylating strength has been tackled. It turns out that both the dimerization and the complexation reactions increase the exothermicity of the global alkylation process. Nevertheless, these reactions can also annihilate the alkylating strength of these co-catalysts due to the formation of highly stable species. In particular, we have found that (i) the alkylating strength of Et2Al–R co-catalysts with R = O–R′ and NH-R′ is weak due to the formation of very stable dimers; (ii) the alkylating strength of Et2Al–S–R′ increases upon adding Lewis bases, whereas Lewis bases make Et3Al less alkylating; and (iii) Et2Al–Cl is less affected by the presence of Lewis bases. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]

After geometry optimization, the electron spectra of indole and four azaindoles are calculated by density functional theory. Available experimental photoemission and excitation data for indole and 7-azaindole are used to compare with the theoretical values. The results for the other azaindoles are presented as predictions to help the interpretation of experimental spectra when they become available. [ABSTRACT FROM AUTHOR]

Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces remains a great challenge. Here, competing reactions of a prochiral alkyne on Ag(111): two-dimensional (2D) homochiral Glaser coupling and heterochiral cross-coupling with a Bergman cyclization step have been examined. We demonstrate control strategies in steering the reactions between the homochiral and heterochiral pathways by tuning the precursor substituents and the kinetic parameters, as confirmed by high-resolution scanning probe microscopy (SPM). Control experiments and density functional theory (DFT) calculations reveal that the template effect of organometallic chains obtained under specific kinetic conditions enhances Glaser coupling between homochiral molecules. In contrast, for the reaction of free monomers, the kinetically favorable reaction pathway is the cross-coupling between two heterochiral molecules (one of them involving cyclization). This work demonstrates the application of kinetic control to steer chiral organic coupling pathways at surfaces. Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces is intriguing but challenging. Here, the authors demonstrate strategies in steering the reactions of prochiral terminal alkynes between the homochiral and heterochiral pathways by tuning the precursor substituents and the kinetic parameters. [ABSTRACT FROM AUTHOR]