Mechanism of Dinitrogen Photoactivation by PPFe Complexes: Thermodynamic and Kinetic Computational Studies.

The PPFe(N)(H) catalyst showed a significant ammonia yield under light irradiation. However, under thermal conditions, the hydrogen evolution reaction (HER) is favored over the nitrogen reduction reaction (NRR), making PPFe(N)(H) an ideal system for studying the competition between both reactions. In this study, we used a series of computational tools to elucidate the photochemical reaction mechanism for the NRR and thermal pathways leading to the HER with this catalyst. We calculated the energy profile for each transformation and estimated the rate constants for each step. Our results, which are consistent with experimental observations, indicate that photoinduced H elimination from PPFe(N)(H) promotes the formation of PPFe(N), which is on-path for NRR. However, this elimination process is kinetically hindered due to high-energy barriers. Furthermore, our calculations reveal enhanced dinitrogen activation upon the conversion of PPFe(N)(H) to PPFe(N).