Through-Space Electrostatic Interactions Surpass Classical Through-Bond Electronic Effects in Enhancing CO2 Reduction Performance of Iron Porphyrins.

In his pioneering work to unravel the catalytic power of enzymes, Warshel has pertinently validated that electrostatic interactions play a major role in the activation of substrates. Implementing such chemical artifice in molecular catalysts may help improve their catalytic properties. In this study, a series of tetra-, di-, and mono-substituted iron porphyrins with cationic imidazolium groups were designed. Their presence in the second coordination sphere helped stabilize the [Fe-CO2 ] intermediate through electrostatic interactions. It was found herein that the electrocatalytic overpotential is a function of the number of embarked imidazolium. Importantly, a gain of six orders of magnitude in turnover frequencies was observed going from a tetra- to a mono-substituted catalyst. Furthermore, the comparative study showed that catalytic performances trend of through-space electrostatic interaction, a first topological effect reported for iron porphyrins, outperforms the classical through-structure electronic effect.

Local ionic liquid environment at a modified iron porphyrin catalyst enhances the electrocatalytic performance of CO2 to CO reduction in water.

In this study we report a strategy to attach methylimidazolium fragments as ionic liquid units on an established iron porphyrin catalyst for the selective reduction of CO2 to CO. Importantly, we found that the tetra-methylimidazolium containing porphyrin exhibits an exalted electrocatalytic activity at low overpotential in water precluding the need for an external proton donor.