Ghosh, Pradyut and Federwisch, Guido and Kogej, Michael and Schalley, Christoph A. and Haase, Detlev and Saak, Wolfgang and Lützen, Arne and Gschwind, Ruth M. (2005) Controlling the rate of shuttling motions in [2]rotaxanes by electrostatic interactions: a cation as solvent-tunable brake. ORGANIC & BIOMOLECULAR CHEMISTRY, 3 (15). pp. 2691-2700. ISSN 1477-0520, 1477-0539
Full text not available from this repository. (Request a copy)Abstract
A series of rotaxanes, with phenolic axle centerpieces and tetralactam macrocycles as the wheels, has been prepared in good yields. The threaded rotaxane structure is confirmed in the gas phase by tandem mass spectrometric experiments through a detailed fragmentation pattern analysis, in solution by NMR spectroscopy, and in the solid state through X-ray crystallography. A close inspection of the H-1, H-1 NOESY and H-1, H-1 ROESY NMR data reveals the wheel to travel along the axle between two degenerate diamide "stations" close to the two stoppers. By deprotonation of a phenolic OH group in the axle centerpiece with Schwesinger's P1 base, surprisingly no additional shuttling station is generated at the axle center, although the wheel could form rather strong hydrogen bonds with the phenolate. Instead, the wheel continues to travel between the two diamide stations. Experimental data from 1H, 1H NOESY spectra, together with theoretical calculations, show that strong electrostatic interactions between the phenolate moiety and the P1 cation displace the wheel from the "phenolate station". The cation acts as a "brake" for the shuttling movement. Instead of suppressing the shuttling motion completely, as observed in other rotaxanes, our rotaxane is the first system in which electrostatic interactions modulate the speed of the mechanical motion between a fast and a slow motion state as a response to a reversible external stimulus. By tuning these electrostatic interactions through solvent effects, the rate of movement can be influenced signicantly, when for example different amounts of DMSO are added to dichloromethane. Besides the shuttling motion, circumrotation of the wheel around the axle is observed and analyzed by variable temperature NMR spectroscopy. Force field and AM1 calculations are in good agreement with the experimental findings.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | NONIONIC TEMPLATE SYNTHESIS; ROTAXANE SYNTHESIS; SUPRAMOLECULAR CHEMISTRY; MOLECULAR MACHINES; TRANSITION-METALS; AMIDE-ROTAXANES; COORDINATION SITES; ANION RECOGNITION; BENZYLIC AMIDE; CENTER PIECES; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Arbeitskreis Prof. Dr. Ruth Gschwind |
| Depositing User: | Petra Gürster |
| Date Deposited: | 02 Feb 2022 09:07 |
| Last Modified: | 02 Feb 2022 09:07 |
| URI: | https://pred.uni-regensburg.de/id/eprint/36789 |
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