Design Principles and Mechanistic Insights for Ionic Liquid-Catalyzed CO₂ Cyclization Under Mild Conditions.

Area of Science:

• Green Chemistry
• Catalysis
• Sustainable Chemical Processes

Background:

• Carbon dioxide (CO2) utilization is crucial for sustainable chemical processes.
• Developing efficient catalysts for CO2 transformation is an active research area.
• Ionic liquids (ILs) show promise for activating CO2.

Purpose of the Study:

• To design and investigate ionic liquids (ILs) for enhanced CO2 activation.
• To develop a synergistic catalytic system using ILs and copper(I) chloride for CO2 utilization.
• To elucidate the catalytic mechanism of ILs in CO2 transformation reactions.

Main Methods:

• Synthesis and screening of various ionic liquids (ILs) for CO2 activation.
• Formation of a catalytic system with copper(I) chloride and selected ILs.
• Carboxylative cyclization reactions of propargylic alcohols with CO2 under mild conditions.
• Theoretical simulations to understand the role of IL structure in catalysis.

Main Results:

• A synergistic catalytic system comprising ILs and copper(I) chloride was successfully developed.
• The system efficiently promoted the carboxylative cyclization of propargylic alcohols with CO2 at room temperature and atmospheric pressure.
• Tetramethyl guanidinium 2,4-dihydroxybenzoate ([TMGH]3[2,4-DHBA]) demonstrated superior catalytic activity (68.9% conversion).
• Theoretical simulations confirmed the crucial role of the IL anion's structure in CO2 adsorption and activation.

Conclusions:

• Ionic liquids with CO2-philic sites significantly enhance cooperative CO2 activation.
• The anion's structural features are critical for CO2 adsorption and activation, correlating positively with catalytic activity.
• This research provides insights for designing efficient and mild catalytic systems for CO2 utilization.