title: Electrochemical Oxidation of [1-X-12-I-CB11Me10-] Anions: Formation of Borenium Ylides [12-Dehydro-1-X-CB11Me10] and Iodonium Ylide Anions [{12-(1-X-CB11Me10-)}2I+].
abstract: Cyclic voltammograms of 12-iodinated icosahedral carborane anions [1-X-12-I-CB11Me10-] (X = H, CH3, C2H5, C3H7, C4H9, C6H13, and COOCH3) show two one-electron anodic oxidation peaks at the Pt electrode in liquid SO2. Oddly, the first is irreversible and the second partially reversible. Mass spectrometry of the principal anionic product of preparative anodic oxidation of [1-H-12-I-CB11Me11-], identical with the anionic product of its reaction with [Et3Si-H-SiEt3]+and/or Et3Si+, allows it to be identified as the iodonium ylide anion [{12-(1-H-CB11Me10-)}2I+]. Its reversible oxidation to a neutral ylide radical [{12-(1-H-CB11Me10•)}{12-(1-H-CB11Me10-)}I+] is responsible for the second peak. A DFT geometry optimization suggests that both the ylide anion and the ylide radical are very crowded and have an unusually large C-I-C valence angle of ∼132°; they are the first compounds with two bulky highly methylated CB11cages attached to the same atom. Molecular iodine is another product of the electrolysis. We propose an electrode mechanism in which initial one-electron oxidation of [1-X-12-I-CB11Me10-] is followed by a transfer of an iodine atom from the B-I bond to SO2to yield a weakly bound radical ISO2•which disproportionates into SO2and I2. The other product is the borenium ylide [12-dehydro-1-X-CB11Me10], which has a strongly Lewis acidic naked vertex in position 12 that rapidly adds to another [1-X-12-I-CB11Me10-] anion to form the observed stable ylide anion [{12-(1-X-CB11Me10-)}2I+]. In acetonitrile, where it presumably exists as a solvent adduct, [12-dehydro-1-X-CB11Me10] has been trapped with H2O and, to a small extent, with MeOH, but not with several other potential trapping agents.
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 3, 182 23 Prague 8, Czech Republic.|Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.
authors.forename: Abdul
authors.identifier: http://orcid.org/0000-0003-0055-7004
authors.initials: A
authors.lastname: Wahab
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Kaleta
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.|Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0215, United States.
authors.forename: Jin
authors.initials: J
authors.lastname: Wen
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Valášek
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 3, 182 23 Prague 8, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Polášek
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic , Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.|Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0215, United States.
authors.forename: Josef
authors.identifier: http://orcid.org/0000-0002-4707-8230
authors.initials: J
authors.lastname: Michl
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 3, 182 23 Prague 8, Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Ludvík