Synergistic ionic liquid-silver catalysis for ambient CO2 conversion to α-alkylidene cyclic carbonates

The carboxylative cyclization of propargylic alcohols with CO₂ constitutes an atom-economical approach for CO₂ utilization, yielding versatile α-alkylidene cyclic carbonates that serve as key intermediates in pharmaceutical synthesis and polymer production. Despite its synthetic value, this transformation typically requires harsh reaction conditions and exhibits unsatisfied efficiency. It is necessary to develop the advanced catalytic systems. A series of glutarimide-based ionic liquids were developed and their synergistic effects with various silver co-catalysts were evaluated. The [BZTMA][GLU]/Ag₂CO₃ system demonstrated exceptional performance, achieving 97.6 % yield under remarkably mild conditions (6 mol% Ag₂CO₃, 30 °C, 0.1 MPa CO₂). Comprehensive structure-activity relationship studies revealed two critical parameters governing catalytic efficiency: the ionic interaction falls within the range of −5.20 to −11.26 kcal mol⁻¹ and the CO₂ absorption exceeds 1.33 mol for per mol of ionic liquid. Mechanistic investigations combining multinuclear ¹H NMR, ¹³C NMR and density functional theory (DFT) calculations elucidated the cooperative activation pathway. The ionic liquid facilitates substrate activation through hydrogen bonding, while the silver complex preferentially activates the alkyne moiety, collectively enabling efficient cyclization through a well-orchestrated catalytic cycle.