Diazapyrenium-containing catenanes and rotaxanes

Abstract

Diazapyrenium units have been incorporated into the π-electron deficient components of four [2]pseudorotaxanes, four [2]catenanes, and two [2]rotaxanes, each having a dioxyarene-based macrocyclic polyether as the π-electron rich component. A dramatic increase in the association constants that characterize the formation of diazapyrenium-containing [2]pseudorotaxanes, relative to those of their bipyridinium-based analogs, was observed in solution studies. These results indicate that the intercomponent non-covalent bonding interactions are reinforced significantly when diazapyrenium, instead of bipyridinium, recognition sites are employed in the π-electron deficient components of this kind of [2]pseudorotaxane. Not surprisingly, therefore, in two asymmetric [2]catenanes which incorporate one diazapyrenium and one bipyridinium recognition site within their tetracationic cyclophane components, the diazapyrenium unit is located inside the cavity of the π-electron rich macrocyclic component as revealed in the solid state by X-ray crystallographic analyses and by ¹H NMR spectroscopic studies in solution. Variable temperature ¹H NMR spectroscopic studies showed that, in the [2]catenanes, the free energy barriers associated with the circumrotation of one macrocyclic component through the cavity of the other and viceversa increase when diazapyrenium, instead of bipyridinium, recognition sites are employed, reflecting the stronger intercomponent non-covalent bonding interactions involving the former.