The maximum turnover frequencies (TOF max) vary among the atropisomers, by a factor of 60 for the ORR and a factor of 5 for CO 2RR. This work reports that each of the four individual atropisomers catalyzes both the ORR and CO 2RR with fast rates and low overpotentials. However, by nature of the mono-ortho substitution pattern, there are more » four possible atropisomers of this metalloporphyrin and thus four unique electrostatic environments. The success of this catalyst is attributed, at least in part, to specific charge-charge interactions between the atomically-positioned o- + groups and the bound substrate. For example, an iron porphyrin bearing four cationic, ortho-N,N,N-trimethylanilinium groups (o- +) has recently been used to catalyze the complex, multi-step O 2 and CO 2 reduction reactions (ORR and CO 2RR) with fast rates and at low overpotentials. One new approach has been to include atomically-positioned, electrostatic motifs in molecular catalysts to stabilize high-energy, charged intermediates. Next-generation energy technologies require improved methods for rapid and efficient chemical-to-electrical energy transformations. Overall, the conclusions provide guidance for the increasingly popular electrostatic ligand designs in catalysis and other reactivity. The inverse half-order dependence of binding constant on ionic strength is proposed as more » a clear marker for an electrostatic effect. The results show that adding electrostatic groups to a catalyst design often results in a complex interplay of multiple effects, including changes in pre-equilibria prior to substrate binding, combinations of through-space and inductive contributions, and effects of ionic strength and solution dielectric. This study is among the first to directly measure the effects of electrostatics on ligand-binding. By comparing Fe( o-TMA) with the related iron-tetraphenylporphyrin, this work examines how covalently positioned charged groups affect substrate binding and other key pre-equilibria of both the ORR and CO 2RR, specifically acetate, dioxygen, and carbon dioxide binding. These reactions involve many different steps, and it is not evident which steps are affected by the four positive charges, or why. For instance, an iron porphyrin bearing four cationic ortho-trimethylanilinium groups, Fe( o-TMA), has been reported to be an exceptional electrocatalyst for both the carbon dioxide reduction reaction (CO 2RR) and the oxygen reduction reaction (ORR). There has been a growing interest in using electrostatic ligand designs-placing charges in the second coordination sphere-to improve molecular reactivity, catalysis, and electrocatalysis. Noncovalent electrostatic interactions are important in many biological and chemical reactions, especially those that involve charged intermediates.
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