March 12 2013

Publications

Complete publications list

 

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Kaleta, J.; Akdag, A.; Crespo, R.; Piqueras, M.-C.; Michl, J. “Evidence for an Intermediate in the Methylation of CB11H12- with MeOTf. Comparison of Electrophilic Substitution in Cage Boranes and in Arenes”, ChemPlusChem 2013, 78, 1174.

ABSTRACT: The trideuteriomethylation of BH vertices in CB11H12-and its derivatives with CD3OTf yields a mixture of B-CD3 and B-CHD2 substitution products, 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 when CD3OTf is used to methylate toluene. According to density functional theory calculations, the intermediate in BH vertex methylation is a three-center bonded σ 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.


MacLeod, M. K.; Michl, J. “Five Stereoactive Orbitals on Silicon: Charge and Spin Localization in the n-Si4Me10∙ Radical Anion by Trigonal Bipyramidalization”, J. Phys. Chem. Lett. 2013, 4, 1649.

ABSTRACT: RIUMP2/def2-TZVPPD calculations show that in addition to its usual conformation with charge and spin delocalized over the Si backbone, the isolated Si4Me10∙ radical anion also has isomeric conformations with localized charge and spin. A structure with localization on a terminal Si atom has been examined in detail. In vacuum, it is calculated to lie 11.5 kcal/mol higher in energy than the charge-and-spin-delocalized conformation, and in water the difference is as little as 1.6 kcal/mol. According to natural orbital and localized orbital analyses, the charge-and-spin-carrying terminal Si atom uses five stereoactive hybrid orbitals in a trigonal bipyramidal geometry. Four are built mostly from 3s and 3p AOs and are used to attach a Si3(CH3)7 and three CH3 groups, whereas the larger equatorial fifth orbital is constructed from 4s and 4p AOs and acts as a non-bonding (radical) hybrid orbital with an occupancy of about 0.65 e.


Douvris, C.; Michl, J. “Update 1 of: Chemistry of the Carba-closo-Dodecaborate(-) Anion, CB11H12”, Chem. Rev. 2013, 113, PR179.


Scholz, F.; Kaletová, E.; Kohutová, A.; Stensrud, E. S.; Ford, W. E.; Mucha, M.; Stibor, I.; Michl, J.; von Wrochem, F. “Formation of n-Alkyl Monolayers by Organomercury Deposition on Gold”, J. Phys. Chem. Lett. 2013, 4, 2624.

ABSTRACT: n-alkyl self-assembled monolayers can be directly attached to gold through C-Au bonds by the deposition of organomercury salts on gold substrates, as shown here using n-butylmercury and n-octadecylmercury tosylate derivatives. The Hg atoms, which are codeposited during this process, are removed by thermal annealing at 95°C, resulting in alkyl monolayers having a significantly enhanced thermal stability compared to alkanethiol monolayers, however a lower degree of conformational order. The monolayer properties are elucidated by X-ray photoemission and IR spectroscopy, STM, ellipsometry and contact angle goniometry.