Tetrabutylphosphonium-Based Ionic Liquid Catalyzed CO2 Transformation at Ambient Conditions: A Case of Synthesis of α-Alkylidene Cyclic Carbonates

A series of tetrabutylphosphonium ([Bu4P]+)-based ionic liquids (ILs) with multiple-site for CO2 capture and activation in their anions, which could efficiently catalyze the cyclization reaction of propargylic alcohols with CO2 at ambient conditions, are reported. Especially, the IL, [Bu4P]3[2,4-OPym-5-Ac], which has three interaction sites for attracting CO2 together with a pKa1 value of 9.13, exhibited the best performance, affording a series of α-alkylidene cyclic carbonates in moderate to good yields. The mechanism exploration demonstrated that IL served as a bifunctional catalyst with anion simultaneously activating CO2 via multiple-site cooperative interactions and the C≡C triple bond in propargylic alcohol via inductive effect, thus resulting in the production of α-alkylidene cyclic carbonates.