Role-Specialized Division of Labor in CO₂ Reduction with Doubly-Functionalized Iron Porphyrin Atropisomers

In enzymes, the active site residues function differently to promote chemical reactions. Such a role-specialized division of labor has been rarely realized by synthetic catalysts. We report herein on catalytic CO₂ reduction with Fe porphyrins decorated with two cationic N,N,N-trimethylbenzylamine groups in cis- or trans-arrangement. The cis-isomer outperforms the trans-isomer and reaches a TOF_max of 4.4×10⁵  s^-1 in acetonitrile using phenol proton source. Theoretical studies revealed that the two cationic units in the cis-isomer are more effective than a single cationic unit to improve the CO₂ binding, and more importantly, they function differently but cooperatively to promote the C-O bond cleavage: one interacts with the CO₂ -adduct, while the other one interacts with the phenol molecule through electrostatic interactions. This work therefore presents a significant example of synthetic catalysts, which boost chemical reactions using a role-specialized strategy for substrate activation.