Iron amino-bis(phenolate) complexes for the formation of organic carbonates from CO2 and oxiranes
A series of iron(III) compounds supported by tetradentate amino-bis(phenolate) ligands were synthesized and characterized using electronic absorption spectroscopy, magnetic moment measurement and MALDI-TOF mass spectrometry. The solid-state structures of 1 and 2 were determined by X-ray diffraction and reveal iron(III) square pyramidal compounds. The complexes were studied as catalysts for the reaction of carbon dioxide and epoxides in the presence of a co-catalyst, under solvent free conditions to yield cyclic carbonates. Catalytic testing with TBAB as a co-catalyst shows that 4 bearing electron withdrawing groups in the ortho and para-positions of the phenolate ring exhibits the highest catalytic activity. Kinetic studies using 1 revealed that the cycloaddition reaction is affected by temperature as expected and the activation energy for propylene carbonate formation is 98.4 kJ mol−1.