Facile synthesis of cyclic carbonates from CO2 and epoxides with cobalt(II)/onium salt based catalysts Original Research Article

Efficient catalytic systems based on the combination of cobalt(II)/onium salts for the coupling reaction of CO2 and epoxides are reported. The catalytic systems work under mild reaction conditions (e.g. 10 bar and 120 °C) and produce cyclic carbonates with high turnover frequencies (TOF) and selectivity. From a series of onium salts, bis(triphenylphosphoranylidene)ammonium chloride proved to be the most active cocatalyst (TOF = 2314), while tetrabutyl ammonium chloride (TOF = 2223) and 1,3-bis(2,4,6trimethylphenyl)imidazolium chloride (TOF = 2174) provided only slightly reduced activities under similar conditions. The influence of various reaction parameters including CO2 pressure, reaction temperature and loading of onium salt was determined. In order to obtain an insight into the catalytic process, the reaction was followed by electrospray ionisation-mass spectrometry. Additionally, in situ FT-IR measurements show that the catalyst is stable even with low loading (0.025 mol%) and as a result, the reaction proceeds steadily over several hours.