Enhanced CO₂/Epoxide Cycloaddition Catalyzed by Pyridine-Substituted Triazole-Quaternary Ammonium Bromide

Area of Science:

• Organic Chemistry
• Catalysis
• Green Chemistry

Background:

• Quaternary ammonium salts with triazole moieties are synthesized.
• The catalytic potential of these compounds as single-component catalysts is explored.

Purpose of the Study:

• To synthesize and characterize novel ionic quaternary ammonium bromides containing triazole groups.
• To evaluate their efficacy as bifunctional catalysts for CO2 cycloaddition with epoxides.
• To investigate the influence of structural modifications on catalytic activity.

Main Methods:

• Synthesis via copper-catalyzed azide-alkyne cycloaddition (CuAAC).
• X-ray crystallographic analysis to determine structural features and intermolecular interactions.
• Catalytic evaluation for CO2/epoxide cycloaddition under varying CO2 pressures.
• Computational studies to elucidate reaction mechanisms and binding modes.

Main Results:

• Successfully synthesized QAS-trzBn4, QAS-trzPic4, and QAS-trzBn2Pic2.
• X-ray crystallography revealed strong Br- interactions with triazolyl and methylene H atoms.
• Pyridyl-triazole catalysts demonstrated superior performance over benzyl-triazole counterparts.
• High conversions (88-100%) to cyclic carbonates were achieved with electron-deficient epoxides using QAS-trzPic4.
• Computational analysis indicated enhanced stabilization of the QAS-trzPic4-CO2-epoxide complex.

Conclusions:

• Ionic quaternary ammonium bromides with triazole moieties are effective catalysts for CO2/epoxide cycloaddition.
• The presence of pyridyl groups significantly enhances catalytic activity and substrate stabilization.
• These catalysts offer a promising route for the synthesis of cyclic carbonates, contributing to green chemistry initiatives.