Protons and Radicals in the Well:
Precursor Complexes and Metal-Ligand Effects on PCET Mechanisms
Proton-coupled electron transfer (PCET) reactions are fundamental to diverse chemical and biological energy conversion processes. Traditionally, the mechanistic analysis of intermolecular, stepwise PCET has viewed hydrogen bonding and proton transfer as mutually exclusive mechanism dominant pathways. In the first part of this talk, we challenge this dichotomy by elucidating a continuous reactivity landscape. Using the electrochemical oxidation of arylenediamines as a model, we demonstrate an EECCC mechanism where proton transfer occurs at equilibrium between H-bonded precursor and successor complexes. By revealing the previously overlooked role of endergonic successor complex dissociation, we show how these coupled equilibria create a thermodynamic energy well that dictates chemical reversibility and bridges the gap between H-bonding and proton transfer.
The second part of the talk explores the outcomes of PCET in the context of carbon-centered reactivity. Specifically, we investigate the PCET-driven generation of stabilized C-centered radicals. While heteroatom-centered PCET is well-documented, extending these principles to carbon requires distinct energetic and structural considerations. We will discuss recent, unpublished findings on how molecular design influences the stabilization of carbon-centered radical intermediates.