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Summary: Tris(trimethylsilyl)cyclopropenylium Cation: The First X-ray
Structure Analysis of an r-Silyl-Substituted Carbocation
Armin de Meijere,* Dietmar Faber, and Mathias Noltemeyer
Institut fu¨r Organische Chemie, and Institut fu¨r Anorganische Chemie, Georg-August-Universita¨t
Go¨ttingen, Tammannstrasse 2-4, D-37077 Go¨ttingen, Germany
Roland Boese* and Thomas Haumann
Institut fu¨r Anorganische Chemie, Universita¨t-GH Essen, Universita¨tsstrasse 5-7,
D-45117 Essen, Germany
Thomas Mu¨ller,§ Michael Bendikov, Eynatte Matzner, and Yitzhak Apeloig*
Department of Chemistry, Technion - Israel Institute of Technology, Technion City, 32000 Haifa, Israel,
and Institut fu¨r Anorganische Chemie der Humboldt Universita¨t Berlin, Hessische Strasse 1-2,
D-10115 Berlin, Germany
Received March 11, 1996 (Revised Manuscript Received September 5, 1996X)
The X-ray crystal structure analysis of tris(trimethylsilyl)cyclopropenylium cation 2 is presented
and compared with the structure and bonding properties obtained by quantum mechanical ab initio
calculations. The calculated bond lengths for 2 are in good agreement with the experimentally
determined ones. The effect of tris-silyl and tris-methyl substitution on the stability of the tris-
substituted cyclopropenylium ions are calculated by using the isodesmic hydride transfer reaction
1. The pKR+ value of 2 is predicted to be 4.
The cyclopropenylium cation is the smallest aromatic
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