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Evidence for an Intermediate in the Methylation of CB11H12- with Methyl Triflate: Comparison of Electrophilic Substitution in Cage Boranes and in Arenes

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    SYSNO ASEP0397510
    Document TypeJ - Journal Article
    R&D Document TypeJournal Article
    Subsidiary JČlánek ve WOS
    TitleEvidence for an Intermediate in the Methylation of CB11H12- with Methyl Triflate: Comparison of Electrophilic Substitution in Cage Boranes and in Arenes
    Author(s) Kaleta, Jiří (UOCHB-X) RID
    Akdag, Akin (UOCHB-X)
    Crespo, R. (ES)
    Piqueras, M. C. (ES)
    Michl, Josef (UOCHB-X) RID
    Number of authors5
    Source TitleChemPlusChem - ISSN 2192-6506
    Roč. 78, č. 9 (2013), s. 1174-1183
    Number of pages10 s.
    Languageeng - English
    CountryDE - Germany
    Keywordsalkylation ; boranes ; carboranes ; electrophilic substitution ; hydrogen scrambling
    Subject RIVCC - Organic Chemistry
    Institutional supportUOCHB-X - RVO:61388963
    UT WOS000324043400037
    EID SCOPUS84883886859
    DOI10.1002/cplu.201300219
    AnnotationThe trideuteriomethylation of BH vertices in CB11H12- and its derivatives with CD3OTf (OTf=triflate, trifluoromethanesulfonate) yields a mixture of BCD3 and BCHD2 substitution products, thus demonstrating the intermediacy of a species with a long enough lifetime for hydrogen scrambling between the boron vertex and the methyl substituent. No such scrambling is observed if CD3OTf is used to methylate toluene. According to density functional theory calculations, the intermediate in BH vertex methylation is a three-center bonded sigma adduct of a methyl cation to the BH bond and the proton scrambling occurs via a transition structure containing a distorted square-pyramidal methane attached axially to a naked boron vertex. The subsequent proton or deuteron loss is presently not understood in detail. A general comparison of electrophilic substitution on closo-boranes and arenes is provided and similarities as well as differences are discussed. A recalculation of the optimized geometry of the CB11Me12. radical produced a second Jahn-Teller distorted minimum and resulted in a somewhat improved agreement between calculated and measured proton hyperfine coupling constants.
    WorkplaceInstitute of Organic Chemistry and Biochemistry
    ContactJana Procházková, janap@uochb.cas.cz, Tel.: 220 183 418 ; Viktorie Chládková, viktorie.chladkova@uochb.cas.cz, Tel.: 232 002 434
    Year of Publishing2014