Kinetic acidity of supramolecular imidazolium salts-effects of substituent, preorientation, and counterions on H/D exchange rates.
The deprotonation of imidazolium salts to N-heterocyclic carbenes is often a decisive step in modern catalytic reactions. Therefore, we studied the H/D exchange of the C2 H of 15 imidazolium-substituted calix[4]arenes and 11 nonmacrocyclic model compounds in methanol/water (97:3). The influence of the counterion, substitution directly on the imidazolium unit or on the preorientating calixarene backbone could be studied. The observed exchange rates might give a rational for the suitability of the imidazolium salts as precursors in the Suzuki coupling.
Division of Organic Chemistry I, University of Ulm, Albert-Einstein-Allee 11, D-89069 Ulm, Germany.
Tilmann
T
Fahlbusch
Markus
M
Frank
Jürgen
J
Schatz
Daniel T
DT
Schühle