Threaded structures based on the benzo-21-crown-7/secondary ammonium salt recognition motif using esters as end groups

It was demonstrated that various threaded structures could be constructed by employing different esters as end groups based on the benzo-21-crown-7/secondary ammonium salt recognition motif. The chemical structures of all synthesized compounds were confirmed by (1)H and (13)C NMR spectroscopy as well as mass spectrometry. Single crystal X-ray analysis revealed that all compounds are threaded structures in the solid state. NMR experiments distinguished the rotaxane-like entities from [2]rotaxanes. The threaded structures capped by linear n-alkyl end groups are rotaxane-like entities. The gradual elongation of the ester alkyl chain tails results in the increased stability of the corresponding threaded structures. When the tail is an isopropyl group, a mechanically interlocked rotaxane can be constructed.