Degenerate rotaxanes with electrostatic barriers
Fahrenbach, Albert C.
Kim, Soo Young
Paxton, Walter F.
Stoddart, J. Fraser
Date of Issue2011
School of Physical and Mathematical Sciences
A synthetic approach to the preparation of 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 rotaxanes 1–5·6PF6, there are Coulombic charge–charge repulsions between these dicationic units and the CBPQT4+ ring in the rotaxanes. Thus, the CBPQT4+ rings in the degenerate 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 rotaxanes 1·6PF6 and 2·6PF6 indicate that the one-electron reduced bipyridinium radical cation in the dumbbell components of the 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.
DRNTU::Science::Chemistry::Organic chemistry::Heterocyclic compounds
Organic and biomolecular chemistry
© 2011 Royal Society of Chemistry. This is the author created version of a work that has been peer reviewed and accepted for publication by Organic and Biomolecular Chemistry, Royal Society of Chemistry. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: http://dx.doi.org/10.1039/c0ob00937g.