Enhancing catalytic strategy for cyclic carbonates synthesized from CO2 and epoxides by using cobaloxime-based double complex salts as catalysts

Abstract

In this study, the novel neutral cobaloximes and corresponding to different cobaloxime-based double complex salts were prepared and for the first time evaluated as an efficient catalyst for the synthesis of cyclic carbonates from epoxides and CO2 without using any organic and inorganic solvents. After seeing the efficient catalytic performance of different forms of the newly synthesized neutral cobaloximes (1−3) and different cobaloxime (4−9) salts, the effect of epoxide, base, temperature, CO2 pressure, reaction time, and amount of catalyst was investigated for these catalysts. The neutral cobaloximes (1−3), double cobaloxime salts (4−6), and their single salts with simple counterions (7−9) were characterized by 1H and 13C NMR spectra, FT-IR spectra, UV-Vis spectra, LC-MS/MS spectrometers, melting point, and elemental analysis techniques. Furthermore, the compounds were utilized as catalysts in the synthesis of cyclic carbonates from epoxide and CO2. The neutral cobaloximes (1−3), double cobaloxime salts (4−6), and their single salts with simple counterions (7−9) showed high catalytic activity (at 100 °C and 1.6 MPa of CO2 pressure) for the carboxylation of epichlorohydrin. The best conversion was performed in the presence of a catalyst (6) (the double cobaloxime salt bearing ethyl) and DMAP as co-catalyst, with a 97.9% yield and 98.4% selectivities.