Polyethers as Complexing Agents in Calcium-Catalyzed Cyclic Carbonate Synthesis

Herein, we report a detailed investigation of alkali and alkaline earth metal salts in combination with polyethers as catalytic systems for the synthesis of cyclic carbonates from epoxides and CO2. CaI2 showed superior activity compared to various other tested alkali and alkaline earth metal salts. Interestingly, in contrast to other catalytic protocols, the presence of hydroxyl groups hampered the reaction. Thus, poly(ethylene glycol) dimethyl ethers (PEG DME) proved to be the most suitable polymer complexing agents. This catalytic protocol is based on a nontoxic and abundant metal as well as readily available polymer coordination agents. Notably, 26 terminal epoxides were converted even at room temperature with CO2 to the corresponding cyclic carbonates in yields up to 99%. Additionally, this system was also effective for the synthesis of 21 challenging internal carbonates based on fossil and renewable feedstock in yields up to 98%. Significantly, at a large scale, namely, 10 g of epoxide, a quantitative yield of cyclic carbonate was isolated in the presence of only 1 mol % catalyst under ambient conditions. Two different recycling strategies were tested which allowed the reuse of the catalyst up to 7 times without the loss of activity.