Preprint of "Dynamic Binding of Alkali-Metal Ions in a Metalloporphyrin Cage: Impact on Redox Properties"

The influence of local electrostatic environments on catalytic reactivity is well established in enzymatic systems, but their systematic implementation in synthetic catalysts remains limited. Here, we investigate the dynamic binding of alkali-metal cations to a cobalt porphyrin cage complex as a strategy to modulate its redox properties and catalytic activity toward CO2 reduction (CO2RR). Electrochemical studies reveal that the Co¹+ → Co0 redox potential is highly sensitive to the identity of the electrolyte cation, with K+ and Cs+ inducing the largest positive shifts (236 mV and 225 mV, respectively), resulting in substantial decreases in CO2RR overpotential. In contrast, Li+, Na+, and Ca²+ produce only minor or moderate effects. Molecular dynamics simulations rationalize these observations in terms of binding mode and dynamics: Li+ remains fully solvated, Na+ interacts weakly with the cage, while K+ and Cs+ bind specifically and symmetrically to the ether-functionalized cage walls, with oxidation state-dependent occupancy. These findings illustrate how alkali-metal ion coordination can be harnessed to modulate molecular electrocatalysts and guide the design of redox-tunable systems.