An improved boron-catalyzed cycloaddition of CO2 to epoxides for the production of five-membered cyclic carbonates under atmospheric versus high-pressure conditions

Abstract

A series of novel boron-based compounds (boronate esters) (1–8) were designed and successfully synthesized by introducing 3-(bromomethyl)phenylboronic acid into the various cis-diols using a Dean-Stark trap to remove the water formed during the esterification reactions. The synthesized boron-based compounds were characterized by 1H, 13C, and 11B NMR, FT-IR, UV–Vis, LC-MS/MS, elemental analysis, TGA-DTA, and melting point measurement techniques. Additionally, the Lewis acidity of the synthesized boronate esters was investigated by the conventional Gutmann-Beckett test. After the boronate esters were characterized in detail by various spectroscopic techniques, these compounds have been used as organocatalysts for the highly efficient conversion of greenhouse gas CO2 to cyclic carbonates under atmospheric versus high-pressure conditions without any solvents. The best conversion was performed in the presence of an organoboron catalyst (3) and DMAP as cocatalyst, with a 90.0 % yield and 97.7 % selectivities under high reactor pressure and with a 45.2% yield and 97.4% selectivities under atmospheric conditions. In addition, after it was determined that the target organoboron catalysts showed high catalytic activity, the effects of epoxide, base, temperature, CO2 pressure, Lewis acidity, reaction time, and amount of catalyst and base on the catalytic conversion were investigated for these catalysts.