Towards the Stepwise Assembly of Molecular Borromean Rings. A Donor-Acceptor Ring-in-Ring Complex

The assembly of molecular Borromean Rings from constitutionally independent rings in a stepwise manner depends on the preparation of robust "ring-in-ring" complexes. The pi-electron rich macrocycle bis-1,5-dinaphtho[50] crown-14 (1) is shown to form a donor-acceptor ring-in-ring complex with the pi-electron poor cyclophane cyclobis(paraquat-4,4'-biphenylene) (2(4+)) in solution. In the crystal superstructure of [1 subset of 2]center dot 4PF(6), CII center dot center dot center dot O interactions between the polyether loops of 1 and the bipyridinium units of 2(4+) could disfavor the threading of dialkylammonium components of a third ring.