Versatile Self-Adapting Boronic Acids for H-Bond Recognition: From Discrete to Polymeric Supramolecules

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Boronic acids exhibit unique dynamic covalent reactivity.
• Interest in aryl boronic acids for materials and supramolecular chemistry is growing.
• Their hydrogen-bonding capabilities remain underexplored.

Purpose of the Study:

• To investigate the hydrogen-bonding complexation of aromatic boronic acids.
• To explore the formation of double-H-bonded DD·AA-type complexes.
• To study these complexes in both solution and solid states.

Main Methods:

• Solution binding studies to determine association constants (K_a).
• Crystallization to analyze solid-state structures (dimeric, trimeric complexes).
• Spectroscopic and crystallographic analysis of complex formation.

Main Results:

• First determination of K_a for ortho-substituted boronic acids (300-6900 M^-1).
• Identification of syn-syn conformer stabilized by frontal H-bonds.
• Observation of "flat" and "T-shaped" complexes based on substitution.
• Formation of supramolecular H-bonded polymeric ribbons from diboronic acid and tetraazanaphthacene.

Conclusions:

• Aromatic boronic acids can form well-defined double-H-bonded complexes.
• Conformational flexibility of boronic acids dictates complex architecture.
• These findings offer potential for metal-free catalysis and organic crystal engineering.