Iron amino-phenolate complexes as catalysts for CO₂ activation

Abstract

The increase of CO₂ emissions in the atmosphere from the burning of fossil fuels has been linked to global climate change. Therefore, finding methods to utilize CO₂, a greenhouse gas, as a C1 feedstock has become of interest. The utilization of CO₂ is beneficial as it is an inexpensive, abundan feedstock with low toxicity, and it can react with epoxides to produce polycarbonates or cyclic carbonates; both of which have several applications. Cyclic carbonates can act as polar aprotic green solvents as well as chemical intermediates for the synthesis of other small molecules and polymers, while polycarbonates can be used to synthesize several biodegradable plastics. Using iron to catalyze these reactions has its own benefits as iron is inexpensive, abundant, and biocompatible. Both the formation of cyclic carbonates and polycarbonates was carried out using iron(III) amino-bis(phenolate) complexes. The iron(III) complexes were characterized by UV-vis spectroscopy, MALDI-TOF MS, and elemental analysis. These complexes were capable of selectively producing cyclic carbonate from carbon dioxide and several epoxides, and reaction parameters could be fine tuned to reduce temperature and reaction time. Polycarbonates were also synthesized selectivity from CO₂ and cyclohexene oxide (CHO) in high yields with moderate molecular weights and low dispersities. Polycarbonate synthesis could be carried out at low pressures and temperatures, which is not common for iron catalyst systems. Isolated polymers were studied further using NMR spectroscopy, GPC analysis, and MALDI-TOF MS.