title: Anion-binding catalysis by electron-deficient pyridinium cations.
abstract: A new activation principle in organocatalysis is presented: halide binding through Coulombic interactions. This mode of catalysis was realized by using 3,5-di(carbomethoxy)pyridinium ions that carry an additional electron-withdrawing substituent on the nitrogen atom, for example, pentafluorobenzyl or cyanomethyl. For the N-pentafluorobenzyl derivative, Coulombic interaction with the pyridinium moiety is complemented in the solid state by anion-π interactions with the perfluorophenyl ring. Bromide and chloride are bound by these cations in a 1:1 stoichiometry. Catalysis of the C-C coupling between 1-chloroisochroman (and related electrophiles) with silyl ketene acetals occurs at -78 °C and at low catalyst loading (2 mol%).
authors.affiliation: Cologne University, Department of Chemistry, Greinstrasse 4, 50939 Cologne (Germany) http://www.berkessel.de. berkessel@uni-koeln.de.
authors.forename: Albrecht
authors.initials: A
authors.lastname: Berkessel
authors.forename: Somnath
authors.initials: S
authors.lastname: Das
authors.forename: Daniel
authors.initials: D
authors.lastname: Pekel
authors.forename: Jörg-M
authors.initials: JM
authors.lastname: Neudörfl
keywords: anion-binding catalysis; anion-π interactions; organocatalysis; organofluorine compounds; pyridinium cations