The balance between electronic and steric effects in the template-directed syntheses of [2]catenanes

Three bis-p-phenylene-34-crown-10 (BPP34C10) derivatives bearing ester groups on one or both of their two aromatic rings have been synthesized. These ester-substituted macrocyclic polyethers bind the paraquat dication in solution more strongly than BPP34C10. In contrast, however, acyclic analogs of these macrocyclic polyethers form much weaker complexes with cyclobis(paraquat-p-phenylene) (CBPQT4+). Likewise, catenane formation is diminished, in parallel with the number and disposition of the ester substituents on the hydroquinone rings of the macrocyclic polyethers. These observations suggest that complex and catenane formation are controlled by opposing recognition features, according to whether the ester-substituted hydroquinone rings assume either a guest or host role in 1:1 complexes with bipyridinium-based species, or lie inside or alongside the CBPQT4+ component in the[2]catenanes. Steric and electronic factors associated with the ester substituents probably account for the opposing trends in the inter-component recognition behavior.