Molecular Models of Atomically Dispersed Uranium at MoS Surfaces Reveal Cooperative Mechanism of Water Reduction.

Single atoms of uranium supported on molybdenum sulfide surfaces (U@MoS) have been recently demonstrated to facilitate the hydrogen evolution reaction (HER) through electrocatalysis. Theoretical calculations have predicted uranium hydroxide moieties bound to edge-sulfur atoms of MoS as a proposed transition state involved in the HER process. However, the isolation of relevant intermediates involved in this process remains a challenge, rendering mechanistic hypotheses unverified. The present work describes the isolation and characterization of a uranium-hydroxide intermediate on molybdenum sulfide surfaces using [(CpMoS)UCp], a molecular model of a reduced uranium center supported at MoS. Mechanistic investigations highlight the metalloligand cooperativity with uranium involved in the water activation pathway. The corresponding uranium-oxo analogue, [(CpMoS)CpU(═O)], was also accessed from the hydroxide cluster via hydrogen atom transfer and from [(CpMoS)UCp] through an alternative direct oxygen atom transfer. These results provide an atomistic perspective on the reactivity of low-valent uranium at molybdenum sulfide surfaces toward water, modeling key intermediates associated with the HER of U@MoS catalysts.