Fluoride ion chelation by a bidentate phosphonium/borane Lewis acid

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Boron Chemistry

Background:

• Phosphonium boranes are explored for their unique chemical properties.
• Understanding Lewis acidity in cationic boron compounds is crucial for designing selective complexation agents.

Purpose of the Study:

• To synthesize and characterize a novel phosphonium borane with enhanced fluoride binding capabilities.
• To investigate the structural and electronic factors governing the high affinity for fluoride.

Main Methods:

• Synthesis of the phosphonium borane iodide salt via alkylation.
• Complexation studies with fluoride ions in methanol.
• Structural analysis using X-ray crystallography.
• Computational studies including NBO and AIM analyses.

Main Results:

• The novel phosphonium borane [1-Mes2B-2-MePh2P-(C6H4)]+ ([2]+) was successfully synthesized.
• The complex [2]+ exhibits exceptionally high fluoride binding affinity, significantly exceeding that of related compounds.
• A strong B-F-->P interaction was identified, contributing to the enhanced fluorophilicity.

Conclusions:

• The high fluorophilicity of [2]+ is attributed to Coulombic and cooperative effects, including a B-F-->P interaction.
• The Lewis acidity of the phosphonium moiety can be leveraged for enhanced fluoride binding through chelation.
• This study presents a new strategy for designing potent fluoride complexation agents.