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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

SYSNO ASEP	0397510
Document Type	J - Journal Article
R&D Document Type	Journal Article
Subsidiary J	Článek ve WOS
Title	Evidence 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, ORCID} Akdag, Akin (UOCHB-X) Crespo, R. (ES) Piqueras, M. C. (ES) Michl, Josef (UOCHB-X)_{RID, ORCID}
Number of authors	5
Source Title	ChemPlusChem. - : Wiley - ISSN 2192-6506 Roč. 78, č. 9 (2013), s. 1174-1183
Number of pages	10 s.
Language	eng - English
Country	DE - Germany
Keywords	alkylation ; boranes ; carboranes ; electrophilic substitution ; hydrogen scrambling
Subject RIV	CC - Organic Chemistry
Institutional support	UOCHB-X - RVO:61388963
UT WOS	000324043400037
EID SCOPUS	84883886859
DOI	10.1002/cplu.201300219
Annotation	The 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.
Workplace	Institute of Organic Chemistry and Biochemistry
Contact	asep@uochb.cas.cz ; Kateřina Šperková, Tel.: 232 002 584 ; Viktorie Chládková, Tel.: 232 002 434
Year of Publishing	2014

Number of the records: 1