Recognition of Bipyridinium-Based Derivatives by Hydroquinone- and/or Dioxynaphthalene-Based Macrocyclic Polyethers:...

A range of pi-electron-rich macrocyclic polyethers incorporating dioxybenzene (hydroquinone) and/or dioxynaphthalene units have been synthesized in good yields by simple two-step procedures. These macrocycles are able to bind bipyridinium-based guests as a result of a series of cooperative noncovalent bonding interactions. These molecular recognition events can be extended to the self-assembly of [2]catenanes incorporating the bipyridinium-based cyclophane, cyclobis(paraquat-p-phenylene), and the macrocyclic polyethers incorporating dioxybenzene and -naphthalene units. The efficiencies of these self-assembly processes were found to depend upon the stereoelectronic features of the pi-electron-rich macrocycles-namely, the nature and the substitution pattern of the aromatic units. X-ray crystallographic analysis of some of these [2]catenanes proved unequivocally the relative geometries of the interlocked components. In addition, in the case of those asymmetric [2]catenanes incorporating two different aromatic units within their macrocyclic polyether components, only one of the expected two translational isomers was observed in the solid state. In particular, in all the structures examined, the 1,4-dioxybenzene and 1,5-dioxynaphthalene units are located within the cavity of the tetracationic cyclophane component in preference to other regioisomeric dioxynaphthalene units that reside alongside. Variable-temperature (1)H NMR spectroscopic investigation of the geometries adopted by these [2]catenanes in solution revealed the same selectivity that was observed for one translational isomer over another in the solid state.