Halogen‐Bonding Heteroditopic [2]Catenanes for Recognition of Alkali Metal/Halide Ion Pairs

Abstract

The first examples of halogen bonding (XB) heteroditopic homo [2]catenanes were prepared by discrete Na + template-directed assembly of oligo(ethylene glycol) units derived from XB donor-containing macrocycles and acyclic bis-azide precursors, followed by a Cu I -mediated azide-alkyne cycloaddition macrocyclisation reaction. Extensive 1 H NMR spectroscopic studies show the [2]catenane hosts exhibit positive cooperative ion-pair recognition behaviour, wherein XB-mediated halide recognition is enhanced by alkali metal cation pre-complexation. Notably, subtle changes in the catenanes' oligo(ethylene glycol) chain length dramatically alters their ion-binding affinity, stoichiometry, complexation mode, and conformational dynamics. Solutionphase and single-crystal X-ray diffraction studies provide evidence for competing host-separated and directcontact ion-pair binding modes. We further demonstrate the [2]catenanes are capable of extracting solid alkalimetal halide salts into organic media.

Alkali Metal Halide Ion‐Pair Binding in Conformationally Dynamic Halogen Bonding Heteroditopic [2]Rotaxanes

“…Synthesis of [2]rotaxanes via metal cation template-directed pseudo- [2]rotaxane formation (Route A) or Cu(I)-mediated active metal templation (Route B). The chemical structures of the previously-reported XB [2]catenanes 34 are included in an inset at the top right. Chemistry-A European Journal…”

“…The cation, anion and ion-pair binding properties of the four rotaxanes were studied by 1 H NMR titrations in 1 : 1 CDCl 3 / CD 3 CN. These conditions are identical to those used previously to investigate the binding properties of the analogous [2]catenanes, [34] enabling a direct comparison of ion-pair binding of the rotaxane and catenane topologies. Upon progressive addition of MBAr 4 F (M = Na + , K + ) to all four rotaxanes, the most prominent changes occurred in the peaks arising from the oligo(ethylene glycol) regions.…”

“…[28][29][30][31][32][33] We recently prepared a series of halogen bonding (XB) heteroditopic [2]catenanes for the recognition of alkali metal halide ion-pairs. [34] The [2]catenanes were prepared via a method pioneered by Chiu et al, [35][36][37][38][39][40][41] exploiting a sodium metal cation to direct the assembly of a pseudo [2]rotaxane complex comprised of an oligo(ethylene glycol)-functionalised XB macrocycle and a bis(azide) precursor. Cyclisation of the latter was achieved via a Cu(I)-catalysed azide-alkyne cycloaddition (CuAAC) reaction to generate the [2]catenane.…”

Dynamic Metalloporphyrin‐Based [2]Rotaxane Molecular Shuttles Stimulated by Neutral Lewis Base and Anion Coordination

“…The prevalence of anions in biological and environmental processes has led to marked interest in the sensing of anions. We and others have exploited controllable dynamic MIM behaviour via an anion recognition stimulus [25–33] . Typically, such dynamic motion arises from an anion being bound in the cavity between macrocycle and axle components.…”

Dynamic mechanostereochemical switching of a co-conformationally flexible [2]catenane controlled by specific ionic guests

“…[42][43][44] On one hand, binding motifs linked by mechanical bonds are still preorganized and the guest association will be strong due to mechanical chelation, and on the other hand, large-amplitude co-conformational rearrangement will be a facile and adaptive mechanism for optimizing the binding as well as responding to external changes. [45][46][47][48][49] In this work, a heteroditopic [2]catenane containing both bipyridine (bpy) and urea motifs for respective cation and anion binding is described. In addition to copper(I) ion that templates its synthesis, the host also displays a strong and selective binding to sulfate anion (log K1 ~ 4.3 and log K2 ~ 3.6) in 5% aqueous DMSO, rendering the catenane as an unusual receptor featuring two structurally different mechanical chelates in the guest-bound forms.…”