Design Principles and Mechanistic Insights for Ionic Liquid‐Catalyzed CO 2 Cyclization Under Mild Conditions

Utilizing carbon dioxide (CO2) as a renewable C1 building block to produce value-added chemicals represents a key strategy for developing greener and more sustainable chemical processes. Herein, a series of ionic liquids (ILs) with excellent CO2 activation capabilities was designed and combined with copper(I) chloride to form a synergistic catalytic system. This system efficiently promoted the carboxylative cyclization of propargylic alcohols with CO2 under mild conditions, such as at room temperature and atmospheric pressure. Among the explored ILs, tetramethyl guanidinium 2,4-dihydroxybenzoate (TMGH32,4-DHBA) was the most effective catalyst, achieving a conversion of 68.9% for the model substrate 2-methyl-3-butyn-2-ol within 12 h. The superior performance of TMGH32,4-DHBA is attributed to the presence of multiple CO2-philic sites on its anionic scaffold, which significantly enhances the cooperative activation of CO2. Furthermore, theoretical simulations revealed that the structural features of the anion play a decisive role in CO2 adsorption and activation, exhibiting a positive correlation with the overall catalytic activity. This work systematically elucidates, from both experimental and theoretical perspectives, the catalytic mechanism of ILs with different cation-anion combinations in CO2 transformation reactions, providing critical insights for the rational design of highly efficient and mild catalytic systems for CO2 utilization.