Correlating Proton Transfer Kinetics and Reorganisation Energies of Metal Hydride Complexes

An attractive solution to combat global climate change is the implementation of renewable energy infrastructures, such as the use of fuel sources produced from sunlight. To realise these goals, identifying and optimising fuel-forming catalysts and their associated reaction intermediates is required. Metal hydride (MH) complexes are pivotal intermediates formed via proton-coupled electron transfer reactions (PCET) within these fuel-forming catalytic cycles. The kinetic and thermodynamic parameters of these fundamental reactions greatly dictate reaction rates and efficiencies. In many cases, these reactions are dictated by sluggish proton transfer (PT) reaction kinetics, hypothesised to result from large PT reorganisation energies. Herein, the reaction kinetics of PT reactions of several MH species were studied to uncover the degree of structural rearrangement accompanying PT and their relevance to hydrogen evolution catalysis. These findings provide insight into key structural and electronic design principles necessary to access next-generation catalysts that operate with high efficiency for MH formation.