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Dhital R.N.,Osaka University | Ehara M.,Research Center for Computational Science | Sakurai H.,Osaka University
Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry

The Palladium nanoclusters (NCs)- catalyzed carbon- carbon bond- forming reaction has emerged as a powerful tool in organic synthesis and has been intensively studied over the past few decades. Recently, a series of gold NC- catalyzed carbon- carbon bond formation has also been introduced even though contamination by PPB levels of palladium impurities has caused debate. Besides the development of gold and palladium NCs, new strategies for the design of gold- based bimetallic catalysts have subsequently been introduced. These burgeoning strategies are remarkable for achieving reaction under ambient conditions, with unique selectivity, and high activity. Among the various bimetallic NCs, Au/Pd has attracted a great deal of attention because of its superior catalytic activities in various types of reaction. In attempts to rationalize the synergistic effects observed with these catalysts, two major factors have been suggested, the ensemble effect and the ligand effect and these effects have been well documented in recently published reviews. This account provides an overview of recent developments in the use of gold- palladium bimetallic NCs for C- X bond activation. A specific objective is to demonstrate the effect of inclusion of Au as nearest heteroatom in the Au/Pd alloy in C- X bond activation from the viewpoint of both experimental observations and quantum chemical calculations. Source

Dhital R.N.,Graduate University for Advanced Studies | Kamonsatikul C.,Mahidol University | Somsook E.,Mahidol University | Bobuatong K.,Research Center for Computational Science | And 4 more authors.
Journal of the American Chemical Society

This paper describes the unique catalytic activity of bimetallic Au/Pd alloy nanoclusters (NCs) for Ullmann coupling of chloroarenes in aqueous media at low temperature. The corresponding reaction cannot be achieved by monometallic Au and Pd NCs as well as their physical mixtures. On the basis of quantum chemical calculation, it was found that the crucial step to govern the unusual catalytic activity of Au/Pd is the dissociative chemisorption of ArCl, which is unlikely in the monometallic Au and Pd NCs. © 2012 American Chemical Society. Source

Takahashi O.,Hiroshima University | Tashiro M.,Japan Institute for Molecular Science | Tashiro M.,Research Center for Computational Science | Ehara M.,Japan Institute for Molecular Science | And 4 more authors.
Chemical Physics

We have investigated the K-2, K-1L-1, and L-2 double core hole (DCH) states of the SiX4 (X = H, F, Cl, and CH3) molecules using the CASSCF and DFT methods aiming at the DCH electron spectroscopy. The Si 1s IPs and DIPs of the present molecules and the generalized relaxation energies are compared and analyzed. The values extracted from the excess relaxation energy agree well with the generalized relaxation energy. The effect of the substituents (H, F, Cl, and CH3) surrounding the central Si atom is examined. The present results illustrate that the DCH electron spectroscopy for K-2, K-1L -1, and L-2 DCH states is useful for the chemical analysis. © 2011 Elsevier B.V. All rights reserved. Source

Takahashi O.,Hiroshima University | Tashiro M.,Japan Institute for Molecular Science | Tashiro M.,Research Center for Computational Science | Ehara M.,Japan Institute for Molecular Science | And 4 more authors.
Journal of Physical Chemistry A

Double-core-hole (DCH) spectra have been investigated for pyrimidine, purine, the RNA/DNA nucleobases, and formamide, using the density functional theory (DFT) method. DCH spectra of formamide were also examined by the complete-active-space self-consistent-field (CASSCF) method. All possible single- and two-site DCH (ssDCH and tsDCH) states of the nucleobases were calculated. The generalized relaxation energy and interatomic generalized relaxation energy were evaluated from the energy differences between ssDCH and single-core-hole (SCH) states and between tsDCH and SCH states, respectively. The generalized relaxation energy is correlated to natural bond orbital charge, whereas the interatomic generalized relaxation energy is correlated to the interatomic distance between the core holes at two sites. The present analysis using DCH spectroscopy demonstrates that the method is useful for the chemical analysis of large molecular systems. © 2011 American Chemical Society. Source

Higashibayashi S.,Graduate University for Advanced Studies | Higashibayashi S.,Japan Institute for Molecular Science | Shrestha B.B.,Graduate University for Advanced Studies | Morita Y.,Japan Institute for Molecular Science | And 9 more authors.
Chemistry Letters

The electrochemical reduction of sumanenetrione by cyclic voltammetry showed stepwise multielectron reduction. Cyclic voltammograms of the stepwise first and second one-electron reduction exhibited reversible waves with associated reduction potentials that were almost equivalent to those of C60. EPR studies of the chemically generated monoanion and dianion of sumanenetrione, in conjunction with theoretical calculations, revealed their structures. The radical anion exhibited C3v symmetric spin delocalization over the entire bowl structure. The radical anion exhibited several absorption bands covering the whole visible to near-IR region. The nature of excitations was assigned by SAC/SAC-CI SD-R calculations. The dianion has a singlet ground state with a large energy gap between the singlet and triplet states. The dianion, too, has C3v symmetry with delocalization over the bowl structure. The major contributing structure of the dianion is the closed-shell configuration rather than the open-shell biradical configuration. © 2014 The Chemical Society of Japan. Source

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