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Flisak Z.,University of Opole | Shiga A.,LUMMOX Research Laboratory
Journal of Organometallic Chemistry | Year: 2012

Ion pair separation is a process that may influence the activity of homogeneous catalysts of olefin polymerization. We have studied the energy of separation for selected titanium and zirconium metallocene and post-metallocene catalytic ion pairs by means of DFT, dispersion-corrected DFT and Paired Interacting Orbitals method (PIO). Unusually weak cation-anion interactions in the bis(phenoxyimine) systems were attributed to strong electron-donating properties of the phenoxyimine ligands. Energy decomposition analysis (EDA) revealed that almost 70% of the counter ion binding energy results from electrostatic interactions. The PIO method made it possible to analyze the nature of the cation-anion binding and associate its strength with the total overlap population of PIOs. © 2012 Elsevier B.V. All rights reserved.

Sato F.,Chiba University | Sato F.,Ehime University | Sato S.,Chiba University | Yamada Y.,Chiba University | And 2 more authors.
Catalysis Today | Year: 2014

Catalytic activity of rare earth oxides (REOs) in the vapor-phase dehydration of 1,4-butanediol to produce 3-buten-1-ol varies with lattice parameters of REOs. In order to clarify the adsorption structure and the reaction mechanism, adsorption energy of 1,4-butanediol on bixbyite REO, such as Sc2O3, Y2O3, Dy2O 3, Ho2O3, and Er2O3, {2 2 2} surface was calculated with density functional theory (DFT), and paired interacting orbitals (PIO) calculation of the adsorption state between 1,4-butanediol and Er2O3 was executed. The DFT study elucidates that the catalytic activity is correlated with adsorption energy. The PIO study clarifies the interactions between the reactive atoms of 1,4-butanediol and Er2O3 surface: tridentate interactions between a position-2 hydrogen atom of diol and an oxygen anion on Er 2O3 and between each OH group of diol and erbium cations on Er2O3, and an intramolecular repulsive interaction between the position-1 carbon atom and the oxygen atom of OH group are observed. These results suggest that the position-2 hydrogen atom is firstly abstracted by a basic oxygen anion and that the position-1 hydroxyl group is subsequently abstracted by an acidic erbium cation. Another OH group on position 4 plays an important role of anchoring the diol to the Er2O3 surface. Therefore, it is proved that the dehydration of 1,4-butanediol over REOs proceeds via acid-base concerted mechanism. © 2013 Elsevier B.V. All rights reserved.

Handzlik J.,Cracow University of Technology | Czernecki M.,Cracow University of Technology | Shiga A.,LUMMOX Research Laboratory | Sliwa P.,Cracow University of Technology
Computational and Theoretical Chemistry | Year: 2012

Mo/SiO 2 and Mo/HZSM-5 olefin metathesis catalysts are theoretically studied using cluster models and the paired interacting orbitals (PIO) method based on the extended Hückel theory. The first step of the catalytic cycle of ethene metathesis, i.e., ethene cycloaddition to the surface Mo methylidene species leading to the molybdacyclobutane formation is analysed. The electronic structure of the Mo ethene-methylidene complexes and the transition states is discussed for different models of the catalysts. It is shown that new MoC and CC bonds are formed in an asynchronous manner. The results support the proposal that the total overlap population between the orbitals of the Mo methylidene and C 2H 4 fragments of the surface ethene complexes can be an approximate reactivity index for supported Mo catalysts of olefin metathesis. © 2012 Elsevier B.V.

Two types of industrial heterogeneous Ziegler-Natta propylene polymerization catalysts, TiCl3 type and MgCl2 supported TiCl4 type, were examined by paired interacting orbitals (PIO) analysis proposed by Fujimoto et al.. The ligand located trans to propylene was found to obstruct the insertion but was essential for the stereospecific insertion of propylene. The ligand located trans to the alkyl group of the active site was found to be necessary for activating the alkyl-Ti bond. The regioselectivity and stereoselectivity of the iso-specific polymerization site on the heterogeneous Ziegler-Natta catalyst system were confirmed. The polymerization activity of MgCl2 supported TiCl4 catalyst was larger than that of the TiCl3 catalyst. [Figure not available: see fulltext.] © 2010 The Polymer Society of Korea and Springer Netherlands.

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