The applied potential at which [Ni(P2PhN2Bn)2(CH3CN)]2+ (P2PhN2Bn = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) catalyzes proton reduction varies as a function of proton source pKa in acetonitrile. By contrast, most molecular catalysts exhibit catalytic onsets at potentials that are pKa-independent. Through a combination of electrochemical and spectroscopic studies, we identify the Nernstian equilibria that give rise to this unique potential-pKa behavior, and generate a “coupled” potential–pKa diagram by identifying the most thermochemically stable species as a function of applied potential and acid pKa. With these data, we are able to more fully understand why this catalyst uniquely exhibits pKa-dependent catalytic activity, identify the balance between proton transfer kinetics and thermodynamic stability of protonated products that influence observed proton-coupled electron transfer reactivity, and predict how this reactivity might be engendered in other molecular catalysts for multi-electron, multi-proton transformations.

Identifying proton-coupled electron transfers that give rise to potential-pKa relationships in catalysis

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.