The role of uranium-arene bonding in H₂O reduction catalysis

The reactivity of uranium compounds towards small molecules typically occurs through stoichiometric rather than catalytic processes. Examples of uranium catalysts reacting with water are particularly scarce, because stable uranyl groups form that preclude the recovery of the uranium compound. Recently, however, an arene-anchored, electron-rich uranium complex has been shown to facilitate the electrocatalytic formation of H₂ from H₂O. Here, we present the precise role of uranium-arene δ bonding in intermediates of the catalytic cycle, as well as details of the atypical two-electron oxidative addition of H₂O to the trivalent uranium catalyst. Both aspects were explored by synthesizing mid- and high-valent uranium-oxo intermediates and by performing comparative studies with a structurally related complex that cannot engage in δ bonding. The redox activity of the arene anchor and a covalent δ-bonding interaction with the uranium ion during H₂ formation were supported by density functional theory analysis. Detailed insight into this catalytic system may inspire the design of ligands for new uranium catalysts.