Multisite activation of epoxides by recyclable CaI₂/N-methyldiethanolamine catalyst for CO₂ fixation: A facile access to cyclic carbonates under mild conditions

The conversion of CO₂ into valuable products has become the inherent part of green and sustainable chemistry. Here we demonstrated an efficient synthesis of cyclic carbonates from epoxides and CO₂ under mild conditions (at 50 °C for 6 h under a CO₂ atmosphere) via the use of CaI₂/N-methyldiethanolamine (MDEA) system as the catalyst. The excellent conversions and selectivities for a broad range of epoxides are achieved under solvent-free conditions even at atmospheric CO₂ pressure and in the presence of water. The catalyst can be simply recycled and reused without obvious loss in its activity. A plausible multisite-activation mechanism is proposed involving hydrogen bond site-assisted and Ca²⁺-promoted ring opening path, in combination with the activation of epoxides by iodide ion.