title: Intramolecular halogen stabilization of silylium ions directs gearing dynamics.
abstract: 2,6-Bis(2,6-difluorophenyl)phenyldimethylsilanium ion (1a) adopts a ground-state C(2) trigonal-bipyramidal geometry in which fluorines from opposing 2,6-difluorophenyl groups coordinate to the apical positions of the pentavalent silyl cation. Exchange of fluorine at silicon occurs by a disrotatory gearing mechanism wherein one fluorine remains coordinated to silicon throughout the circuit. The "cogwheel" transition state is C(s)-symmetric, with one ring having a dihedral angle of 0 degrees and the other a dihedral angle of 90 degrees. This correlated dynamic process is a function of the coordinating halogen. The chloro derivative (1b) adopts a similar ground-state geometry, but exchange of chlorine at silicon follows a conrotatory process.
authors.affiliation: Organic Chemistry Institute, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Paola
authors.initials: P
authors.lastname: Romanato
authors.forename: Simon
authors.initials: S
authors.lastname: Duttwyler
authors.forename: Anthony
authors.initials: A
authors.lastname: Linden
authors.forename: Kim K
authors.initials: KK
authors.lastname: Baldridge
authors.forename: Jay S
authors.initials: JS
authors.lastname: Siegel