Building Shape-Persistent Arylene Ethynylene Macrocycles as Scaffolds for 1,4-Diiodobutadiyne

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Chemical Crystallography

Background:

• Macrocyclic chemistry enables the design of host molecules for specific guest binding.
• Halogen bonding is an important non-covalent interaction driven by electrophilic regions on halogen atoms.

Purpose of the Study:

• To design and synthesize shape-persistent macrocycles capable of binding 1,4-diiodobutadiyne.
• To investigate the binding mechanism and strength using computational and experimental methods.

Main Methods:

• Synthesis of arylene ethynylene macrocycles.
• Density functional theory (DFT) calculations for binding prediction.
• Carbon-13 nuclear magnetic resonance (¹³C NMR) titrations for experimental validation.

Main Results:

• Successful synthesis of two shape-persistent macrocycles.
• DFT calculations predicted halogen bonding between pyridine moieties and 1,4-diiodobutadiyne.
• ¹³C NMR titrations confirmed binding, yielding a binding constant (K = 10.5 L mol^-1).
• The binding constant is significantly higher than other halogen bonds, indicating cooperative binding.

Conclusions:

• The designed macrocycles effectively bind 1,4-diiodobutadiyne through cooperative halogen bonding.
• A fully inserted geometry of the guest molecule within the macrocycle was demonstrated.
• This work highlights the potential of macrocyclic scaffolds for selective guest recognition via halogen bonding.