Molecular Necklaces Formed Through Zn2+-Templated Binding of Macrocycles with Dynamically Formed Imines as Guest Recognition Sites

Abstract

Herein we demonstrate an "in-ring establishing" strategy for assembling interlocked molecules through dynamic imine formation, "establishing" the host recognition sites in situ. Using Zn²⁺ ions to template the assembly of a pyridine-containing macrocycle with semidumbbell-shaped triazole-containing aldehyde and amine derivatives, we obtained the corresponding [2]rotaxane in high yield (85 %) after subsequent imine reduction (NaBH₄) and amine protonation (NH₄PF₆). We performed the same three steps (assembly, reduction, protonation) to prepare a stable and highly symmetrical [5]molecular necklace ([5]MN) from 12 components (two almost-90°-oriented dialdehydes, two almost-90°-oriented diamines, four macrocycles, four Zn²⁺ ions) in an overall yield of 69 %.

Keywords: catenanes; dynamic covalent bonds; imines; molecular necklaces; rotaxanes.