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 π-expanded substituents (5,10,15,20-tetrakis(pyren-1-yl)porphyrinato iron(III) chloride (Fe-Py)), π-extended substituents (5,10,15,20-tetrakis((1,1'-biphenyl)-4-yl)porphyrinato iron(III) chloride (Fe-PPh)) and π-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 π-expanded substituents exhibits the highest activity among these complexes.