Chalcogen Bonding Macrocycles and [2]Rotaxanes for Anion Recognition

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Materials Science

Background:

• Electron-deficient heavy chalcogen atoms form chalcogen bonds (ChB) with Lewis bases, enabling supramolecular interactions.
• The application of ChB in solution-phase anion binding is emerging, particularly in acyclic systems.
• Incorporating ChB donors into macrocyclic structures offers expanded possibilities for host-guest chemistry.

Purpose of the Study:

• To explore the 5-(methylchalcogeno)-1,2,3-triazole motif as a novel ChB donor for anion binding within macrocyclic hosts.
• To synthesize and characterize mechanically interlocked [2]rotaxanes featuring ChB-donor groups.
• To investigate the anion binding capabilities of these novel systems in organic and aqueous environments, elucidating the role of ChB.

Main Methods:

• Synthesis of 5-(methylchalcogeno)-1,2,3-triazole containing macrocycles and rotaxanes.
• ¹H NMR spectroscopy for structural characterization and anion binding studies.
• Density Functional Theory (DFT) calculations and molecular dynamics simulations to understand binding mechanisms and selectivity.
• ⁷⁷Se and ¹²⁵Te NMR spectroscopy to probe the electronic environment of chalcogen atoms during anion recognition.

Main Results:

• Successful incorporation of the 5-(methylchalcogeno)-1,2,3-triazole motif into robust macrocyclic structures.
• Demonstration of endotopic chelation of copper(I) by the chalcogen atoms within the macrocycle cavity.
• Preparation of the first mechanically interlocked [2]rotaxanes incorporating ChB-donor groups using an active metal template strategy.
• ¹H NMR and molecular modeling confirmed the dominant role of ChB in anion binding by the rotaxane hosts.
• Observation of unprecedented charge-assisted ChB-mediated anion binding in aqueous mixtures, with distinct recognition behavior compared to chalcogen-free analogues.
• DFT and molecular dynamics simulations revealed that anion selectivity in aqueous media is governed by anion hydrophilicity and the hydration of binding units.
• ⁷⁷Se and ¹²⁵Te NMR directly showed how anion binding influences the local electronic environment of the chalcogen atoms.

Conclusions:

• The 5-(methylchalcogeno)-1,2,3-triazole motif is a versatile ChB donor for constructing complex macrocyclic and mechanically interlocked host systems.
• ChB plays a crucial role in solution-phase anion recognition, even in aqueous environments.
• The developed rotaxane systems exhibit tunable anion binding selectivity influenced by both ChB interactions and solvent effects.
• Heteronuclear NMR spectroscopy provides direct evidence for ChB-mediated anion recognition and its impact on the electronic properties of the donor atoms.