Degenerate [2]rotaxanes with electrostatic barriers

• Main Authors: Fahrenbach, Albert C., Paxton, Walter F., Li, Hao, Zhao, Yanli, Kim, Soo Young, Stoddart, J. Fraser
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2011
• Subjects: DRNTU::Science::Chemistry::Organic chemistry::Heterocyclic compounds
• Online Access: https://hdl.handle.net/10356/93839; http://hdl.handle.net/10220/7009
• Institution: Nanyang Technological University

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.