Preorganized anion traps for exploiting anion-π interactions: an experimental and computational study

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Computational Chemistry

Background:

• Development of neutral anion receptors is crucial for sensing and separation.
• Anion-π interactions offer a promising, yet underexplored, binding motif.
• Preorganization of receptors enhances binding affinity and selectivity.

Purpose of the Study:

• To design and synthesize novel neutral anion receptors, A(F) and B(F), exploiting anion-π interactions.
• To evaluate the binding capabilities of A(F) and B(F) towards chloride and bromide anions.
• To computationally quantify the contributions of different interactions to anion binding.

Main Methods:

• Synthesis of fluorinated isoindoline (A(F)) and carbazole (B(F)) derivatives.
• Host-guest complexation studies using NMR spectroscopy and Job plots.
• X-ray crystallography to determine complex structures.
• Computational analysis using local correlation methods.

Main Results:

• Receptors A(F) and B(F) demonstrate effective binding of chloride and bromide anions.
• Crystal structures reveal precise guest positioning within the receptor cleft.
• Solution NMR indicates potential host isomerism affecting binding dynamics for A(F).
• Association constants up to 960 M⁻¹ were determined for B(F) in specific solvents.
• Anion-π interactions were quantified as a significant contributor (approx. 50%) to binding energy.

Conclusions:

• A(F) and B(F) are effective neutral receptors utilizing preorganization and anion-π interactions for halide binding.
• The study quantifies the energetic contribution of anion-π interactions in these systems.
• These findings advance the design principles for neutral anion receptors.