Translational Isomerism in Some Two- and Three-Station [2]Rotaxanes.
The template-directed syntheses of three [2]rotaxanes are described. They all have dumbbell components, with both hydroquinone and resorcinol rings inserted into polyether chains terminated by tetraarylmethane stoppers, that become encircled during the key self-assembly processes by the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), with its two pi-electron deficient bipyridinium units. It has been demonstrated by low-temperature (1)H NMR spectroscopy that the pi-electron deficient tetracationic cyclophane has a remarkably high preference to reside around the hydroquinone ring in these molecular shuttles. This observation illustrates how a very small constitutional difference-hydroquinone versus resorcinol recognition sites-can lead to the overwhelming preference for one translational isomer over another in this particular range of [2]rotaxanes.
Amabilino
David B.
DB
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
Ashton
Peter R.
PR
Boyd
Sue E.
SE
Gómez-López
Marcos
M
Hayes
Wayne
W
Stoddart
J. Fraser
JF