Institute of Theoretical Chemistry

Vienna, Austria

Institute of Theoretical Chemistry

Vienna, Austria
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Wang S.,Institute of Theoretical Chemistry
International Journal of Quantum Chemistry | Year: 2017

Cobalt-based catalysts can replace the homologous group-9 rhodium-based ones. Herein, we used density functional theory (DFT) calculations to predict the synthesis of 2,3-dihydropyridines using α,β-unsaturated oxime pivalates and alkenes catalysed by [Cp*CoOAc]+ instead of [Cp*RhOAc]+. The catalytic cycle involves reversible acetate-assisted metalation-deprotonation, migratory insertion of alkenes, and reductive elimination/N-O cleavage. The migratory insertion of alkenes was determined to be the rate-determining step, and the reaction is irreversible due to the strongly exergonic reductive elimination/N-O cleavage. When using the CF3-substituted Cp*Co(III) catalyst, the apparent activation energy indicates that the title reaction can proceed at higher temperatures. Electron-withdrawing substituent groups on Cp* facilitate the reaction. In contrast, substituting phenyl with the electron-deficient p-CF3-phenyl at the 2-position of α,β-unsaturated oxime pivalate hinders the reaction, and so does the use of polarized alkenes with electron-withdrawing substituent groups © 2017 Wiley Periodicals, Inc.

Mauksch M.,Institute of Theoretical Chemistry | Tsogoeva S.B.,The Interdisciplinary Center
Physical Chemistry Chemical Physics | Year: 2017

Due to the absence of open subshells (unlike transition metal compounds), stable high spin organic molecules are rare and are mostly limited to states of low multiplicity. As an alternative to high multiplicity polyradicals and polycarbenes, with their small energetic separation of different spin isomers, it is demonstrated that Baird's rule of 4n electron aromaticity in the triplet electronic state allows, in principle, the design of polycyclic high spin organics with high spin multiplicity in the electronic ground state and a large energetic separation for other spin states. Energy spacing between spin isomers is dictated here by the aromaticity or antiaromaticity of individual cycles (taking into account all p electrons), rather than by a spin Hamiltonian alone (accounting only for unpaired spin electrons). As a proof of concept, dyads of the cyclopentadienyl cation (which has been reported to possess a triplet ground state) have been computationally found to possess a quintet electronic ground state with two ferromagnetically coupled Baird aromatic rings (with SCF-GIAO NICS(0) = -4.6 and -4.4, respectively; "NICS" is "nucleus independent chemical shift") at the CASMP2(8,10)/6-311G∗//CASSCF(8,10)/6-311G∗level, which is 48.3 kcal mol-1 lower in energy than the C2 open shell singlet with two antiaromatic rings (with NICS = +17.4), and 19.7 kcal mol-1 below the triplet which has one aromatic and one antiaromatic ring, with NICS = -4.8 and +45.0, respectively. Triads of the cyclopentadienyl cation in linear and branched topologies are also proposed to be ground states of maximum spin multiplicity by computations at the DFT and CCSD(T)/6-31G//UB3LYP/6-311G∗levels. © the Owner Societies 2017.

Mauksch M.,Institute of Theoretical Chemistry | Tsogoeva S.B.,The Interdisciplinary Center
Physical Chemistry Chemical Physics | Year: 2017

Polycyclic fully conjugated hydrocarbons in which aromatics are fused to aromatics-or aromatics to antiaromatics-are important as potential organic semiconductors. Herein we explore the only remaining fusion pattern of antiaromatics to antiaromatics. It is shown computationally that the central antiaromatic unit (cyclobutadiene or pentalene) in such a three-unit polycyclic hydrocarbon, generated by fusion of three antiaromatic molecules, turns aromatic according to magnetic shielding (NICS) criteria. The resulting neutral 4N electron molecules possess a 4N π electron perimeter with pronounced CC bond length equalization (as indicated by the HOMA geometric index) and significant aromatic stabilization energies (computed using the isomerization-stabilization method) and could be promising synthetic targets with small HOMO-LUMO gaps. © the Owner Societies 2017.

Shi R.,Institute of Theoretical Chemistry | Qian H.-J.,Institute of Theoretical Chemistry | Lu Z.-Y.,Institute of Theoretical Chemistry
Physical Chemistry Chemical Physics | Year: 2017

The controllable distribution of nanoparticles (NPs) in polymer nanocomposites (PNCs) is a challenge in materials science. An important method is grafting chains that are chemically identical to the polymer matrix on NPs. By performing comprehensive molecular dynamics simulations, the self-assembly behavior of polymer-grafted NPs in a polymer matrix is investigated in this study. The relationship between the grafted chain length N, grafting density σ and the NPs' self-assembly morphologies is studied. Phase diagrams of the NP self-assembly structures for both unimodal and bimodal grafted NP systems are constructed on a parameter space, where P is the matrix polymer chain length. NP self-assembly structures of strings, connected/sheet and small clusters are identified in different regions. In order to quantitatively characterize the NP self-assembly morphology, we define a morphological measurement parameter which characterizes the distribution of the Voronoi cell volume of the NPs. Using this parameter, we discuss the influences of both long and short grafted chains on the dispersion of bimodal polymer-grafted NPs in a polymer melt. We find that the short grafted chains can not only shield the NP surface from the polymer matrix but also elongate the long grafted chains into the polymer matrix, therefore favoring a better dispersion of NPs. Our results also indicate that the bimodal grafted NPs will not be fully dispersed until the short grafted chains are dense enough to elongate the long grafted chains, hence forming a wetting NP/matrix interface. © the Owner Societies 2017.

Zhang J.-P.,Jilin Institute of Chemical Technology | Jin L.,Jilin Institute of Chemical Technology | Zhang H.-X.,Institute of Theoretical Chemistry
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica | Year: 2011

The geometries of ground and excited states of a series of ruthenium complexes [Ru(iph)(L)2]2+ (L=cpy (1), mpy (2), npy (3); iph=2,9-di(1-methyl-2-imidazole)-1,10-phenanthroline, cpy=4-cyano pyridine, mpy=4-methyl pyridine, npy=4-N-methyl pyridine) were optimized by the Becke's three-parameter functional and the Lee-Yang-Parr (B3LYP) functional and unrestricted B3LYP methods, respectively. Timedependent density functional theory (TD-DFT) method at the B3LYP level together with the polarized continuum model (PCM) were used to obtain their absorption and phosphorescent emission spectra in acetone media based on their optimized ground and excited-state geometries. The results revealed that the optimized structural parameters agreed well with the corresponding experimental results. The highest occupied molecular orbitals were localized mainly on the d orbital of the metal and the π orbital of the iph ligand for 1 and 2, and the npy ligand for 3, while the lowest unoccupied molecular orbitals were mainly composed of π* orbital of the iph ligand. Therefore, the lowest-lying absorptions and emissions were assigned to the metal to ligand charge transfer (MLCT)/intra-ligand charge transfer (ILCT) transition for 1 and 2, and the ligand to ligand charge transfer (LLCT) transition for 3. The lowest-lying absorptions are at 509 nm (1), 527 nm (2), and 563 nm (3) and the phosphorescence emissions at 683 nm (1), 852 nm (2), and 757 nm (3). The calculation results show that the absorption and emission transition characteristics and the phosphorescence color can be changed by altering the π electron-donating ability of the L ligand. © Editorial office of Acta Physico-Chimica Sinica.

Richter M.,Institute of Theoretical Chemistry | Mai S.,Institute of Theoretical Chemistry | Marquetand P.,Institute of Theoretical Chemistry | Gonzalez L.,Institute of Theoretical Chemistry
Physical Chemistry Chemical Physics | Year: 2014

Ab initio molecular dynamics simulations have been performed in order to investigate the relaxation dynamics of uracil after UV excitation in gas phase. Intersystem crossing (ISC) has been included for the first time into time-dependent simulations of uracil, allowing the system to relax in the singlet as well as in the triplet states. The results show a qualitatively different picture than similar simulations that include singlet states only. The inclusion of ISC effectively quenches the relaxation to the singlet ground state and instead privileges transitions from the low-lying nπ∗ state (S1) to a ππ∗ triplet state (T2) followed by rapid internal conversion to the lowest triplet state. © 2014 the Partner Organisations.

Cao H.,CAS Beijing National Laboratory for Molecular | Huang Y.,Institute of Theoretical Chemistry | Liu Z.,CAS Beijing National Laboratory for Molecular
Proteins: Structure, Function and Bioinformatics | Year: 2016

To clarify the interplay between the binding affinity and kinetics of protein-protein interactions, and the possible role of intrinsically disordered proteins in such interactions, molecular simulations were carried out on 20 protein complexes. With bias potential and reweighting techniques, the free energy profiles were obtained under physiological affinities, which showed that the bound-state valley is deep with a barrier height of 12-33 RT. From the dependence of the affinity on interface interactions, the entropic contribution to the binding affinity is approximated to be proportional to the interface area. The extracted dissociation rates based on the Arrhenius law correlate reasonably well with the experimental values (Pearson correlation coefficient R=0.79). For each protein complex, a linear free energy relationship between binding affinity and the dissociation rate was confirmed, but the distribution of the slopes for intrinsically disordered proteins showed no essential difference with that observed for ordered proteins. A comparison with protein folding was also performed. © 2016 Wiley Periodicals, Inc.

Potzel O.,Institute of Theoretical Chemistry | Taubmann G.,Institute of Theoretical Chemistry
Journal of Solid State Chemistry | Year: 2011

In this work, we considered the pressure induced B1B2 phase transition of AB compounds. The DFT calculations were carried out for 11 alkaline halides, 11 alkaline earth chalcogenides and the lanthanide pnictide CeP. For both the B1 and the B2 structures of each compound, the energy was calculated as a function of the cell volume. The transition pressure, the bulk moduli and their pressure derivatives were obtained from the corresponding equations of state. The transition path of the Buerger mechanism was described using roots of the transition matrix. We correlated the computed enthalpies of activation to some structure defining properties of the compounds. A fair correlation to Pearsons hardness of the ions was observed. © 2011 Elsevier Inc. All rights reserved.

Zheng Y.,Northeast Normal University | Xiong T.,Northeast Normal University | Lv Y.,Northeast Normal University | Zhang J.,Northeast Normal University | And 2 more authors.
Organic and Biomolecular Chemistry | Year: 2013

A combination of computational and experimental methods was carried out to elucidate the mechanism of palladium-catalyzed water-assisted benzylic C-H amination with N-fluorobenzenesulfonimide (NFSI), which involved the oxidative addition of PdII to PdIV-species as a rate-limiting step, followed by water-assisted concerted metalation-deprotonation (CMD) of the PdIV complex and water-assisted reductive elimination (RE) processes, and then a nucleophilic addition process to generate the final product and complete the catalytic cycle. The stability of the PdIV complex could be ascribed to the suitable ligands with strong σ-donors and resistance to decomposition, as well as being sufficiently bulky because the water-clusters assembled the ligands through hydrogen bonds to act as one multidentate ligand. Calculation results suggested that water also plays a crucial role as a proton transferring bridge in water-assisted CMD and RE processes. The corresponding experimental findings substantiate the expectation. Additionally, NFSI was found to act as both the oxidant and the nitrogen source to facilitate the reaction, while the steric effect of the bulky -N(SO2Ph)2 group contributed to circumventing the o-C-H amination. In this reaction, we investigated a novel spiro-cyclopalladation intermediate, formed by the reaction of the PdIV centre with pristine-carbon instead of ortho-carbon, which might be valuable for our understanding and further development of transition metal catalyzed C-H functionalization. © 2013 The Royal Society of Chemistry.

Liu P.,Institute of Theoretical Chemistry | Song K.,Institute of Theoretical Chemistry | Zhang D.,Institute of Theoretical Chemistry | Liu C.,Institute of Theoretical Chemistry
Journal of Molecular Modeling | Year: 2012

The detailed mechanisms of catalytic CO oxidation over Au 2 - and AuAg - dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au 2 - and AuAgdimers catalyze the reaction according to the similar monocenter Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg -, the Au site is more active than the Ag site, and the calculated energy barrier values for the ratedetermining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au 2 - catalytic reaction. The better catalytic activity of bimetallic AuAg - dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for lowtemperature CO oxidation than either pure metallic catalyst. © Springer-Verlag 2011.

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