Synergistic Porosity and Charge Effects in a Supramolecular Porphyrin Cage Promote Efficient Photocatalytic CO2 Reduction

We present a supramolecular approach to catalyzing photochemical CO2 reduction through second‐sphere porosity and charge effects. An iron porphyrin box (PB) bearing 24 cationic groups, FePB‐2(P), was made via post‐synthetic modification of an alkyne‐functionalized supramolecular synthon. FePB‐2(P) promotes the photochemical CO2 reduction reaction (CO2RR) with 97 % selectivity for CO product, achieving turnover numbers (TON) exceeding 7000 and initial turnover frequencies (TOFmax) reaching 1400 min−1. The cooperativity between porosity and charge results in a 41‐fold increase in activity relative to the parent Fe tetraphenylporphyrin (FeTPP) catalyst, which is far greater than analogs that augment catalysis through porosity (FePB‐3(N), 4‐fold increase) or charge (Fe p‐tetramethylanilinium porphyrin (Fe‐p‐TMA), 6‐fold increase) alone. This work establishes that synergistic pendants in the secondary coordination sphere can be leveraged as a design element to augment catalysis at primary active sites within confined spaces. We present a supramolecular strategy to enhance photochemical reduction of CO2 to CO leveraging synergy between multiple second‐sphere interactions. Post‐synthetic click chemistry enables modular synthesis of porous porphyrin organic cages bearing 24 cationic groups. The coordinated use of both porosity and charge to augment CO2 reduction activity beyond additive effects results in fast and selective catalysis under low CO2 concentrations.