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Issue 7, 2011
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Degenerate [2]rotaxanes with electrostatic barriers

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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 CBPQT4+ 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 2·6PF6 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.

Graphical abstract: Degenerate [2]rotaxanes with electrostatic barriers

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Publication details

The article was received on 27 Oct 2010, accepted on 24 Dec 2010 and first published on 23 Feb 2011

Article type: Paper
DOI: 10.1039/C0OB00937G
Citation: Org. Biomol. Chem., 2011,9, 2240-2250
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    Degenerate [2]rotaxanes with electrostatic barriers

    H. Li, Y. Zhao, A. C. Fahrenbach, S. Kim, W. F. Paxton and J. F. Stoddart, Org. Biomol. Chem., 2011, 9, 2240
    DOI: 10.1039/C0OB00937G

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