Reducing the CO₂ content in the atmosphere and moderating global warming will require a massive and cost-effective transformation of CO₂ into fuel or building blocks – quite an extraordinary feat! To address this challenge, chemists are taking inspiration from particularly efficient natural metalloenzymes, such as carbon monoxide dehydrogenase, which reversibly reduces CO₂ into CO.

This is why researchers at the CEA-Joliot (I2BC) have been developing over the last few years a family of bio-inspired iron porphyrin catalysts, which are particularly interesting for the catalytic electro-reduction of CO₂.

In natural enzymatic reactions, electrostatic interactions play a major role in through-space stabilization of reaction intermediates, while the role of electrons through the structure of the catalyst is more modest. But what about these bio-inspired catalysts?

To find out, the chemists designed and synthesized a series of iron porphyrins. Cationic imidazolium groups were introduced into these porphyrins (by varying their number), as well as a derivative containing only one imidazolium and six fluorine atoms within electron-withdrawing groups. By comparing the efficiency of these different catalysts, they were able to determine the respective contributions of through-space electrostatic interactions as well as through-structure electronic effects.

The researchers observed an additive effect of electrostatic interactions on the catalytic properties of iron porphyrins. In the case of the derivative containing fluorine atoms, the effects of the electrostatic interactions surpassed the classical electronic effects.

This work, performed in collaboration with the Institut de Chimie Moléculaire et des Matériaux d'Orsay, helps to better understand the relationship between the structure and reactivity of iron porphyrin-based catalysts, and paves the way for the development of innovative chemical combinations.