The sustainable catalytic conversion of CO2 into value-added chemicals by using cobaloxime-based double complex salts as efficient and solvent-free catalysts

Abstract

Cobalt(III)-based catalysts for CO2 fixation are widely applied for the synthesis of cyclic carbonates from epoxides and CO2 under suitable and solvent-free conditions. Inspired by the enhancing catalyst strategy for highly efficient CO2 conversion into useful products, here we show that the cobaloximes (1–3) and corresponding to different double cobaloxime salts (4–6), and their single salts with simple counterions (7–9) were prepared and evaluated as an efficient catalyst for the coupling of CO2 and epoxides into cyclic carbonates. The structure of synthesized target cobaloximes was characterized using a combination of 1H, 13C, and 11B NMR spectra, FT-IR spectra, UV–Vis spectra, LC-MS/MS spectrometers, melting point, and elemental analysis techniques. Although the prepared cobaloxime-based catalytic systems were studied in a wide range of epoxide substrates, the highest catalytic activity was observed in the conversion of epichlorohydrin under suitable conditions. After seeing highly efficient catalytic conversion and selectivity of the newly synthesized cobaloximes (1–3) and different cobaloxime-based double complex salts (4–9), the effect of epoxide, base, reaction time, temperature, and CO2 pressure was investigated for these catalysts. The best conversion was performed in the presence of a catalyst (6) (the double cobaloxime salt bearing 4-t-butyl) and DMAP as a co-catalyst, with a 98% yield and 99% selectivities.