The meso -substituent electronic effect of Fe porphyrins on the electrocatalytic CO 2 reduction reaction.

We report Fe porphyrins bearing different meso -substituents for the electrocatalytic CO 2 reduction reaction (CO 2 RR). By replacing two and four meso -phenyl groups of Fe tetraphenylporphyrin (FeTPP) with strong electron-withdrawing pentafluorophenyl groups, we synthesized FeF 10 TPP and FeF 20 TPP, respectively. We showed that FeTPP and FeF 10 TPP are active and selective for CO 2 -to-CO conversion in dimethylformamide with the former being more active, but FeF 20 TPP catalyzes hydrogen evolution rather than the CO 2 RR under the same conditions. Experimental and theoretical studies revealed that with more electron-withdrawing meso -substituents, the Fe center becomes electron-deficient and it becomes difficult for it to bind a CO 2 molecule in its formal Fe 0 state. This work is significant to illustrate the electronic effects of catalysts on binding and activating CO 2 molecules and provide fundamental knowledge for the design of new CO 2 RR catalysts.