Second-Sphere Biomimetic Multipoint Hydrogen-Bonding Patterns to Boost CO2 Reduction of Iron Porphyrins.

Inspired by nature's orchestra of chemical subtleties to activate and reduce CO2 , we have developed a family of iron porphyrin derivatives in to which we have introduced urea groups functioning as multipoint hydrogen-bonding pillars on the periphery of the porphyrinic ring. This structure closely resembles the hydrogen-bond stabilization scheme of the carbon dioxide (CO2 ) adduct in the carbon monoxide dehydrogenase (CODH). We found that such changes to the second coordination sphere significantly lowered the overpotential for CO2 reduction in this family of molecular catalysts and importantly increased the CO2 binding rate while maintaining high turnover frequency (TOF) and selectivity. Entrapped water molecules within the molecular clefts were found to be the source of protons for the CO2 reduction.