Enhanced CO ₂ Electroreduction Through Electrostatic Functionalization of Iron Porphyrin

Abstract Among the various strategies chemists are adopting from enzymatic active sites—particularly those involved in CO 2 activation, the role of electrostatic effects stands out as a promising yet underexplored area. In this study, we have designed an iron porphyrin molecular catalyst for CO 2 reduction, incorporating an imidazolium group positioned ortho to one of the phenyl substituents at the meso position of the porphyrin ring. This strategic placement allows us to probe the electrostatic influence exerted by the positively charged imidazolium moiety on the catalytic activity. Our study revealed that this newly designed catalyst overrides the catalytic performance of the unsubstituted congener by two orders of magnitude operating at similar potential. Furthermore, we can access five distinct reduction states through chemical reduction, all of which were characterized by EPR spectroscopy. Notably, we identified that following the formation of the formally Fe(0) complex, an imidazolyl radical was also generated. This finding indicates that the nature of the cationic group, here the imidazolium fragment, can also actively participate in the redox chemistry and must be taken into account when considering the overall electronic properties of the catalyst.