Recyclable Single-Component Rare-Earth Metal Catalysts for Cycloaddition of CO2 and Epoxides at Atmospheric Pressure

Ionic rare-earth metal complexes 1–4 bearing an imidazolium cation were synthesized, which, as single-component catalysts, showed good activity in catalyzing cyclic carbonate synthesis from epoxides and CO2. In the presence of 0.2 mol % catalyst, monosubstituted epoxides bearing different functional groups were converted into cyclic carbonates in 60–97% yields under atmospheric pressure. In addition, bulky/internal epoxides with low reactivity yielded cyclic carbonates in 40–95% yields. More importantly, the readily available samarium complex 2 was reused for six successive cycles without any significant loss in its catalytic activity. This is the first recyclable rare-earth metal-based catalyst in cyclic carbonate synthesis.