RECOGNITION OF BIPYRIDINIUM-BASED DERIVATIVES BY HYDROQUINONE-BASED AND OR DIOXYNAPHTHALENE-BASED MACROCYCLIC POLYETHERS - FROM INCLUSION COMPLEXES TO THE SELF-ASSEMBLY OF [2]CATENANES/

A range of pi-electron-rich macrocyclic polyethers incorporating dioxy benzene (hydroquinone) and/or dioxynaphthalene units have been synthes ized in good yields by simple two-step procedures. These macrocycles a re able to bind bipyridinium-based guests as a result of a series of c ooperative noncovalent bonding interactions. These molecular recogniti on events can be extended to the self-assembly of [2] catenanes incorp orating the bipyridinium-based cyclophane, cyclobis(paraquat-p-phenyle ne), and the macrocyclic polyethers incorporating dioxybenzene and -na phthalene units. The efficiencies of these self-assembly processes wer e found to depend upon the stereoelectronic features of the pi-electro n-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 inter locked components. In addition, in the case of those asymmetric [2] ca tenanes incorporating two different aromatic units within their macroc yclic polyether components, only one of the expected two translational isomers was observed in the solid state. In particular, in all the st ructures examined, the 1,4-dioxybenzene and 1,5-dioxynaphthalene units are located within the cavity of the tetracationic cyclophane compone nt in preference to other regioisomeric dioxynaphthalene units that re side alongside. Variable-temperature H-1 NMR spectroscopic investigati on of the geometries adopted by these [2] catenanes in solution reveal ed the same selectivity that was observed for one translational isomer over another in the solid state.