Conversion of dilute CO2 to cyclic carbonates at sub-atmospheric pressures by a simple indium catalyst

The transformation of CO2 to value added commodity chemicals presents an impactful strategy to obtain products that are less dependent on fossil fuels. In this study, indium tribromide (InBr3) mixed with tetrabutylammonium bromide (NBu4Br) co-catalyst has been identified as a simple, highly efficient catalyst for the synthesis of cyclic carbonates from epoxides and CO2 at sub-atmospheric pressures, room temperature, and under solvent-free conditions. The InBr3/NBu4Br catalytic system is tolerant toward different functional groups with high conversions and >99% selectivity for cyclic carbonate without resorting to high pressures and temperatures. Moreover, a combination of in situ IR, NMR spectroscopy, and substrate labelling experiments enabled the proof of key catalytic steps and detection of reaction intermediates to elucidate the reaction mechanism. This technology represents a potential scalable system for the utilization of waste CO2.