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

Three bis-p-phenylene-34-crown-10 (BPP34C10) derivatives bearing ester grou ps on one or both of their two aromatic rings have been synthesized. These ester-substituted macrocyclic polyethers bind the paraquat dication in solu tion more strongly than BPP34C10. In contrast, howe ver, acyclic analogs of these macrocyclic polyethers form much weaker complexes with cyclobis(para quat-p-phenylene) (CBPQT(4+)). Likewise, catenane formation is diminished, in parallel with the number and disposition of the eater substituents on th e hydroquinone rings of the macrocyclic polyethers. These observations sugg est that complex and catenane formation are controlled by opposing recognit ion features, according to whether the ester-substituted hydroquinone rings assume either a guest or host role in 1:1 complexes with bipyridinium-base d species, or lie inside or alongside the CBPQT(4+) component in the[2]cate nanes. Steric and electronic factors associated with the ester substituents probably account for the opposing trends in the inter-component recognitio n behavior. (C) 2001 Elsevier Science Ltd. All rights reserved.