Takudrei

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Rotaxane or pseudorotaxane? Effects of small structural variations on the deslipping kinetics of rotaxanes with stopper groups of intermediate size

A. Affeld, G. M. Hübner, C. Seel, C. A. Schalley— 2001

Three series of rotaxanes have been synthesized variously by slipping synthesis, in which axis and wheel are melted in admixture, by recognition of amide groups inside the macrocyclic wheel, or by an anionic template method, in which the stoppering phenolates are hydrogen bonded to the wheel and then joined by reaction with a semi-axle. The 3,5-di-tert-butylphenyl stopper used for most of these rotaxanes is large enough to permit their isolation, but still allows the wheel to deslip from the axle under appropriate conditions. The deslipping activation parameters for all rotaxanes are derived from H-1 NMR kinetic measurements and have been evaluated from the Arrhenius equation as well as according to Eyring theory. Small structural variations give rise to surprising effects on the activation parameters. Firstly, in some examples, the axle length affects the deslipping barrier, although the size complementarity of stopper and wheel remain unchanged. Secondly, stopper flexibility has an important influence on the deslipping rate. Thirdly, exchange of a carbonamide for a sulfonamide in the wheel significantly reduces the entropic costs of the deslipping, resulting in a pronounced deslipping rate enhancement. Fourthly, intramolecular hydrogen bonding within the wheel decelerates deslipping by a factor of more than 10(4).

Title039
Rotaxane or pseudorotaxane? Effects of small structural variations on the deslipping kinetics of rotaxanes with stopper groups of intermediate size
AuthorA. Affeld, G. M. Hübner, C. Seel, C. A. Schalley
Date20010801
IdentifierDOI 10.1002/1099-0690(200108)2001:15<2877::AID-EJOC2877>3.0.CO;2-R
Source(s)
CitationEur. J. Org. Chem. 2001, 2877-2890
TypeText