Degenerate [2]rotaxanes with electrostatic barriers

Hao Li, Yan Li Zhao, Albert C. Fahrenbach, Soo Young Kim, Walter F. Paxton, J. Fraser Stoddart

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

A synthetic approach to the preparation of [2]rotaxanes (1-5·6PF6) incorporating bispyridinium derivatives and two 1,5-dioxynaphthalene (DNP) units situated in the rod portions of their dumbbell components that are encircled by a single cyclobis(paraquat-p-phenylene) tetracationic (CBPQT4+) ring has been developed. Since the π-electron-deficient bispyridinium units are introduced into the dumbbell components of the [2]rotaxanes 1-5·6PF6, there are Coulombic charge-charge repulsions between these dicationic units and the CBPQT 4+ ring in the [2]rotaxanes. Thus, the CBPQT4+ rings in the degenerate [2]rotaxanes exhibit slow shuttling between two DNP recognition sites on the 1H NMR time-scale on account of the electrostatic barrier posed by the bispyridinium units, as demonstrated by variable-temperature 1H NMR spectroscopy. Electrochemical experiments carried out on the [2]rotaxanes 1·6PF6 and 2·6PF 6 indicate that the one-electron reduced bipyridinium radical cation in the dumbbell components of the [2]rotaxanes serves as an additional recognition site for the two-electron reduced CBPQT2(+) diradical cationic ring. Under appropriate conditions, the ring components in the degenerate rotaxanes 1·6PF6 and 2·6PF6 can shuttle along the recognition sites - two DNP units and one-electron reduced bipyridinium radical cation - under redox control.

Original languageEnglish (US)
Pages (from-to)2240-2250
Number of pages11
JournalOrganic and Biomolecular Chemistry
Volume9
Issue number7
DOIs
StatePublished - Apr 7 2011

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry

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