We have developed a molecular platform that harnesses synergistic cation effects to overcome fundamental limitations in electrocatalytic oxygen reduction. Integrating concepts from heterogeneous and enzymatic catalysis, our porphyrin ligand (L1) positions redox-inactive cations within the secondary coordination sphere of iron centers. This framework incorporates mono- (Li⁺, Na⁺, K⁺), di- (Ca²⁺, Ba²⁺, Sr²⁺), and trivalent (Eu³⁺, Y³⁺, La³⁺) cations in defined spatial relationships to the catalytic site. Through multi-technique characterization (NMR, UV-vis, IR, XAS, and electrochemistry), we quantified how these cations modulate electronic structure and redox properties.
The catalytic behavior of our iron complex (Fe1) disrupts the conventional inverse relationship between overpotential and selectivity in oxygen electroreduction. While traditional catalysts face an obligatory trade-off between these parameters, our system achieves selective four-electron reduction pathways with substantially reduced overpotentials—a long-sought goal in electrocatalysis. Mechanistic investigations reveal that this performance stems from concerted electrostatic perturbations and secondary coordination effects that stabilize key reaction intermediates. This approach enables fine-tuning of transition states without modifying the primary metal center.
This molecular architecture provides a versatile platform for rational catalyst design across diverse transformations. By controlling non-covalent interactions in the secondary coordination sphere, our approach offers new design principles for optimizing reactivity, selectivity, and efficiency in molecular catalysis, potentially enabling breakthroughs in energy conversion and chemical synthesis.