Molecular meccano, 48 [(+)] - Probing co-conformational changes in chiral [2]rotaxanes by 1H-NMR spectroscopy

Peter R. Ashton, José A. Bravo, Françisco M. Raymo, J. Fraser Stoddart*, Andrew J P White, David J. Williams

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

The template-directed syntheses of three [2]rotaxanes possessing either chiral centers or elements of planar chirality, in one of their two mechanically interlocked components, have been realized and their solid-state structures have been analyzed by X-ray crystallography. In one instance, an enantiomerically pure dumbbell-shaped component incorporating a 1,5- dioxynaphthalene recognition site and two (1R,2S,5R)-menthyl stoppers was employed to template the formation of the achiral tetracationic cyclophane, cyclobis(paraquat-p-phenylene). The resulting enantiomerically pure [2]rotaxane was isolated in a yield of 55%. In the other two instances, an achiral 1,5-dioxynaphthalene-based dumbbell-shaped component was employed to template the formation of bipyridinium-based cyclophanes possessing either one or two elements of planar chirality. The resulting [2]rotaxane, possessing one element of planar chirality, was isolated as a racemate in a yield of 24%. The related [2]rotaxane, possessing two elements of planar chirality, was isolated as a mixture of a meso form and an enantiomeric pair in an overall yield of 28%. The 1H-NMR-spectroscopic analysis of this mixture revealed a diastereoisomeric ratio of 4:1. A degenerate coconformational change was identified by variable-temperature 1H-NMR spectroscopy in all [2]rotaxanes. The symmetry loss arising from the introduction of one or two elements of planar chirality enabled the elucidation of the mechanism of this dynamic process in two instances.

Original languageEnglish (US)
Pages (from-to)899-908
Number of pages10
JournalEuropean Journal of Organic Chemistry
Issue number4
DOIs
StatePublished - Apr 1999

Keywords

  • Co-conformation
  • Molecular recognition
  • Planar chirality
  • Rotaxanes
  • Template-directed synthesis

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry

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