Highly effective capture and subsequent catalytic transformation of low-concentration CO2 by superbasic guanidines

Abstract

Herein, we present a highly efficient and convenient approach for carbon dioxide (CO₂) capture and catalytic transformation under mild conditions using N,N′-bis(imidazolyl)guanidines (BIGs, organoguanidine-based strong superbases) as the organocatalyst, even from simulated flue gas (10% CO₂/90% N₂, v/v) or directly from dry air (∼400 ppm CO₂). The zwitterionic BIG–CO₂ adducts were successfully isolated and characterized. X-ray single crystal analysis revealed the bent geometry of the binding CO₂ in the BIG–CO₂ adduct with an O–C–O angle of 129.7° and increased C–O bond distances (1.253 and 1.237 Å) in comparison with free CO₂. Notably, the resulting BIG–CO₂ adducts were found to be capable of catalyzing the novel cycloaddition of various propiolamidines with simulated flue gas to generate functionalized (4E,5Z)-4-imino-5-benzylideneoxazolidine-2-ones in good yields and excellent selectivity.