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