Syntheses and CO2 reduction activities of π-expanded/extended iron porphyrin complexes

The construction of molecular catalysts that are active toward CO2 reduction is of great significance for designing sustainable energy conversion systems. In this study, we aimed to develop catalysts for CO2 reduction by introducing aromatic substituents to the meso-positions of iron porphyrin complexes. Three novel iron porphyrin complexes with pi-expanded substituents (5,10,15,20-tetrakis(pyren-1-yl) porphyrinato iron(III) chloride (Fe-Py)), pi-extended substituents (5,10,15,20-tetrakis((1,1'-biphenyl)-4-yl) porphyrinato iron(III) chloride (Fe-PPh)) and pi-expanded and extended substituents (5,10,15,20-tetrakis(4-(pyren-1-yl) phenyl) porphyrinato iron(III) chloride (Fe-PPy)) were successfully synthesized, and their physical properties were investigated by UV-vis absorption spectroscopy and electrochemical measurements under Ar in comparison with an iron complex with a basic framework, 5,10,15,20-tetrakis(phenyl) porphyrinato iron(III) chloride (Fe-Ph). Moreover, the catalytic activity of the complexes was studied by electrochemical measurements under CO2, and it is found that the complex with the pi-expanded substituents exhibits the highest activity among these complexes.