Anion Recognition by Benzoxaborole

Area of Science:

• Supramolecular Chemistry
• Boron Chemistry
• Anion Recognition

Background:

• Benzoxaborole (1) is a versatile Lewis acid with potential applications in anion sensing.
• Understanding its binding interactions with various anions is crucial for designing new recognition systems.
• Phenylboronic acid (PBA) serves as a benchmark for comparing binding affinities and modes.

Purpose of the Study:

• To determine the binding types (H-bonding, coordinate) and stability constants of benzoxaborole (1) with mono- and di-anions.
• To compare the anion binding behavior of benzoxaborole (1) with that of phenylboronic acid (PBA).
• To elucidate the factors governing the preferential binding mode of anions to benzoxaborole (1).

Main Methods:

• ¹H and ¹¹B NMR titrations were employed to study anion complexation in DMSO or MeCN.
• Density Functional Theory (DFT) calculations were used to optimize complex structures and confirm binding preferences.
• Analysis focused on stability constants and coordination/hydrogen bonding interactions.

Main Results:

• Benzoxaborole (1) is a stronger Lewis acid and weaker H-bond donor than PBA.
• Anions like F^-, HPO₄^2-, and PhPO₃^2- preferentially form coordinate bonds with benzoxaborole (1).
• Benzoxaborole (1) forms both H-bonded and coordinate complexes with SO₄^2-, unlike PBA which only forms H-bonded complexes.

Conclusions:

• Benzoxaborole (1) exhibits diverse anion binding modes, including significant coordinate bonding, differentiating it from PBA.
• Steric hindrance and anion basicity are key factors influencing the preferred binding type (coordinate vs. H-bonding).
• The findings provide insights into the rational design of benzoxaborole-based anion recognition agents.