Uhl Werner, Vinogradov Andrej, Grimme Stefan
Institut für Anorganische und Analytische Chemie der Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany.
J Am Chem Soc. 2007 Sep 12;129(36):11259-64. doi: 10.1021/ja073657u. Epub 2007 Aug 18.
On treating di(tert-butyl)butadiyne with dimethylaluminum hydride under different reaction conditions two unprecedented organoelement compounds, containing cationic carbon atoms stable in solution at room temperature, were obtained. A vinyl cation (2) in which the cationic carbon atom is part of a C=C double bond was produced from 3 equiv of the hydride, whereas a large excess of the hydride yielded an aliphatic carbocation (3) by complete hydroalumination of all C-C multiple bonds. Each compound is zwitterionic with the hydride counterion effectively coordinated in a chelating manner by two strongly Lewis acidic aluminum atoms. In agreement with quantum-chemical calculations the C-H bond activation and the stabilization of the cationic species are further supported by a strong hyperconjugation with Al-C single bonds. This considerably diminishes the effective positive charge at the respective cationic carbon atoms.
