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.