Using peak shift analysis to elucidate proton-coupled electron transfer mechanisms and kinetics for cobalt hydride formation

Formation of metal hydride complexes is key to many proton-coupled electron transfer (PCET) reactions involved in the catalytic activation of small molecules. In many catalytic cycles, metal hydride intermediates play a key role in product selectivity, making control over the kinetics of metal hydride formation an important design consideration. However, isolating these elementary steps and quantifying the kinetics within complex catalytic cycles remain challenging, and mechanistic understanding is often required for meaningful kinetic analysis. In this tutorial, we outline approaches to probe the mechanisms and kinetics of PCET reactions and illustrate their applications through the use of catalyst model complexes capable of forming metal hydrides. Using cobalt cyclopentadienyl diphosphine complexes as representative systems, electroanalytical methods, particularly peak shift analysis of cyclic voltammetry data, are utilized to determine reaction pathways and quantify proton transfer kinetics. Complementary computational studies further support mechanistic interpretation. By unifying insights from mechanistic, kinetic, and computational studies of six cobalt complexes, this tutorial aims to provide a practical framework for studying PCET reactions in fuel-forming catalysis mediated through metal hydride intermediates, to guide the rational design of future molecular catalysts.