Spectroscopic and Theoretical Insights into H₂ Activation on Uranium Monoxide: Homolytic H₂ Cleavage Mediated by Intermediate OU(η²‑H₂)

Elucidating molecular-level interactions between dihydrogen (H₂) and uranium oxides reveals fundamental insights into the intrinsic H₂ activation mechanisms underlying processes such as heterogeneous catalysis over uranium oxides and corrosion of uranium induced by H₂. Herein, the reactions of H₂ with uranium monoxide (UO) molecules have been investigated via a combination of matrix-isolation infrared spectroscopy and quantum chemical calculations. A side-on bonded H₂ complex, OU­(η²-H₂), is identified at 3733.7 and 800.3 cm^–1. This species is regarded as a crucial intermediate along H₂ activation pathways. Bonding analysis reveals cooperative U­(π_5f/6d) → H₂(σ*) π_// backdonation and U ← H₂(σ) σ donation in OU­(η²-H₂) that facilitate the activation of the H₂ moiety. Upon λ > 550 nm photoirradiation, OU­(η²-H₂) isomerizes into H₂UO, indicating the homolytic H₂ cleavage on UO. Mechanistic details of H₂ adsorption and dissociation on UO molecules have been further elucidated.