title: Kinetic versus thermodynamic control during the formation of [2]rotaxanes by a dynamic template-directed clipping process.
abstract: A template-directed dynamic clipping procedure has generated a library of nine [2]rotaxanes that have been formed from three dialkylammonium salts-acting as the dumbbell-shaped components-and three dynamic, imino bond-containing, [24]crown-8-like macrocycles-acting as the ring-shaped components-which are themselves assembled from three dialdehydes and one diamine. The rates of formation of these [2]rotaxanes differ dramatically, from minutes to days depending on the choice of dialkylammonium ion and dialdehyde, as do their thermodynamic stabilities. Generally, [2]rotaxanes formed by using 2,6-diformylpyridine as the dialdehyde component, or bis(3,5-bis(trifluoromethyl)benzyl)ammonium hexafluorophosphate as the dumbbell-shaped component, assembled the most rapidly. Those rotaxanes containing this particular electron-deficient dumbbell-shaped unit, or 2,5-diformylfuran units in the macroring, were the most stable thermodynamically. The relative thermodynamic stabilities of all nine of the [2]rotaxanes were determined by competition experiments that were monitored by (1)H NMR spectroscopy.
authors.affiliation: Fraunhofer Institute for Applied Polymer Research Geiselbergstr. 69, 14476 Golm, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Horn
authors.forename: Johannes
authors.initials: J
authors.lastname: Ihringer
authors.forename: Peter T
authors.initials: PT
authors.lastname: Glink
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart