Iron is one of the metals that can convert cyclic carbonate by coupling CO2 and epoxide, there are some studies using a Schiff base and an aminophenolate based iron complexes. But these complexes limit on modifying tetradentate ligand system, so we investigate new types of Fe-ligand systems based on iminopyridine or polypyridine binding to Fe center in a bidentate or tridentate manner. Notably, Fe(II)-iminopyridine complexes are easy to modify structure in tuning their steric and electronic properties by modification the framework of the ligand. In our reaction condition, Fe(II) complexes have an axial halogen which can be dissociable to form empty site of metal center acting as Lewis acid for epoxide activation. At 60 oC, relatively low temperature, the combined use of iron complexes and tetrabutyl ammonium bromide (TBAB) resulted in an efficient catalytic system for the synthesis of cyclic carbonates under low CO2 pressure (0.5 MPa) and solvent-free conditions. Fe(II)-polypyridine complexes having their own nucleophilic halide source also converted styrene oxide to cyclic carbonate in the absence of TBAB under the elevated reaction temperature (100 oC). Particularly, Fe(II) complex bearing bpy-6,6’-diol (dhbpy) ligand showed higher efficiency, suggesting the additional role of hydrogen bonding attraction in epoxide activation.

Fe(II)-polypyridine/iminopyridine complexes as efficient catalysts for the conversion of CO2 into cyclic carbonate

256th National Meeting (2018)

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