Buttressing effects on haloarene deprotonation: a merely kinetic or also thermodynamic phenomenon?
(2,6-Dichlorophenyl)- and (2,6-dibromophenyl)trialkylsilanes undergo hydrogen/metal interconversion preferentially at the 4- rather than 3-position. However, the organometallic species generated by such a "meta metalation" are thermodynamically less stable (i.e., more basic) than those that would result from an ordinary "ortho metalation". This was demonstrated by equilibration experiments based on permutational halogen/metal interconversion. A new buttressing effect can explain the unprecedented regioselectivity. It is supported by X-ray structures that reveal marked deformations of the benzene ring in halophenylsilanes. [structure: see text]
Gorecka
Joanna
J
Institute of Chemical Sciences and Engineering (ISIC), Ecole Polytechnique Fédérale, (BCh), CH-1015 Lausanne, Switzerland.
Heiss
Christophe
C
Scopelliti
Rosario
R
Schlosser
Manfred
M