Bidentate deltamide hydrogen bond donor catalyzed cycloaddition of carbon dioxide into epoxide

The cycloaddition of carbon dioxide into epoxides through hydrogen bond donor (HBD) and halide nucleophile as a binary catalyst to afford cyclic carbonates has become a key strategy for fixing carbon dioxide. A series of bidentate HBD catalysts of deltamides featured with N–H bond were synthesized and evaluated in the cycloaddition of CO₂ to epoxides (CCE) reactions. The influences on the catalytic activity were scrutinized, which included tunable substituents, types of nucleophiles, reaction time, temperature and the loading of the catalyst. The HBD catalyst 2,3-bis((4-(trifluoromethyl)phenyl)amino)cycloprop-2-en-1-one (DT3) with substituted –CF₃ group in combination with tetrabutylammonium iodide (NBu₄I) showed the best performance with 95 % conversion of styrene oxide into cyclic carbonate under mild conditions (0.1 MPa, 100 °C and 12 h). Substrate applicability of the catalyst is illustrated by the conversion of quantity terminal epoxides with excellent yields and quantitative selectivity. ¹H NMR titration spectra and control studies were employed to probe a reasonable activation mechanism of the cycloaddition of CO₂ to epoxides reactions.