The reaction of CO2 and epoxides to give cyclic carbonates or polycarbonates is a promising method of utilizing CO2 as a C-1 feedstock. We developed new chromium complexes of tripodal amino-bis(phenolate) ligands as effective catalysts for the coupling of CO2 and epoxides such as cyclohexene oxide and propylene oxide to form cyclic or poly(carbonates). By tuning the reaction conditions, catalyst selectivity for either cyclic carbonate or polycarbonate formation can be controlled. Mechanistic studies of the process by in situ IR spectroscopy, and gas phase characterization of possible intermediates by MALDI-TOF and electrospray ionization mass spectrometry, showed the importance of the steric and electron-donor properties of the pendent neutral donor arm of the ligand. The ability of the ligand to hinder formation of six-coordinate Cr(III) intermediates results in higher catalyst activity and modifications of the pendent donor appear more influential than modifications of the phenolate donors. Furthermore, the formation of block co-polymers can be achieved by initiation of lactide polymerization at hydroxyl-terminated polycarbonate chains. The mechanistic aspects of this reaction supported by the spectroscopic evidence are the focus of this presentation.

Mechanistic spectroscopic analysis of carbonate synthesis from CO2 and epoxides using amino-bis(phenolate) complexes

2019 Spring National Meeting

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