Molecular Catalysts

Studying the formation of transition metal hydride complexes via proton-coupled electron transfer is important for developing next-generation molecular catalysts for hydrogen evolution.

Daniel Kurtz and Professor Jillian Dempsey from the Dempsey Group report in work published in Inorganic Chemistry, the study of stepwise photoinduced reduction and protonation of [CoIICp(dppe)]+ (Cp = cyclopentadienyl, dppe = 1,2-bis(diphenylphosphino)ethane) to form the corresponding hydride complex [HCoIIICp(dppe)]+

Reaction intermediates were optically tracked using transient absorption spectroscopy, and a combination of experimental fitting and kinetic simulations was used to determine apparent rate constants for electron transfer and proton transfer with a range of acid sources. A linear free energy relationship is observed between measured apparent proton transfer rate constants and acid strength, but marked differences from previously electrochemically determined protonation rate constants are found.

These key variations highlight the nuanced differences that can exist between electrochemical and photochemical methods applied to kinetic and mechanistic analyses of PCET reactions, and, by extension, analysis of electrocatalytic and photocatalytic systems.