The efficient and reusable imidazolium-organoboron catalysts for green CO₂ insertion reactions in solvent-free under atmospheric and high-pressure conditions

Organoboron compounds that are available in industrial and scientific research were investigated as organocatalysts for the coupling reaction of CO2 into cyclic carbonates as fine chemicals in solvent-free and under sustainable green atmospheric and high-pressure conditions (1 atm and 1.6 MPa, 100 degrees C, 2 h). This work synthesized a series of imidazolium-organoboron catalysts (IBC1-IBC8) using the eco-friendly and metal-free methodology and characterized by various analysis techniques. These techniques were NMR (1H, 13C, and 11B), UV-Vis, FT-IR, Mass spectrometry, C/H/N analysis, and melting point measurement together with thermal gravimetric analysis (TGA-DTA), respectively. After that, the Lewis acidity of the synthesized imidazoliumorganoboron catalysts, which is important for catalytic CO2 conversion studies, was investigated by the traditional Gutmann-Beckett test, and the Lewis acidity order of the target compounds was found at range 54.96-50.36 ppm. In the presence of 0.1 mol% imidazolium-organoboron catalyst (IBC8) and 0.2 mol% DMAP as co-catalyst, 4-chloromethyl-1,3-dioxalan-2-one was obtained as cyclic carbonate from epichlorohydrin in 44.9 % yield and 97.6 % selectivity (1 atm and 100 degrees C) and in an excellent 97 % yield with 98.9 % selectivity (1.6 MPa and 100 degrees C) in 2 h without any solvents. After the imidazolium-organoboron catalyst (IBC8) showed efficient catalytic conversion and high selectivity, the effect of different parameters, including the effect of substrate, Lewis acid-base, reaction time, reaction temperature, CO2 pressure, and catalyst amount, was studied for this catalyst. According to the obtained catalytic conversion results, it was also determined that the optimum Cat./ ECH ratio for CO2 cycloaddition reactions is 1/1000.