p<i>K</i>_a of alcohols dictates their reactivity with reduced uranium-substituted thiomolybdate clusters

The uranium-substituted thiomolybdate cluster, (Cp*3Mo3S4)UCp*, has been demonstrated as a model for water reduction by single uranium atoms supported on a molybdenum sulfide surface (U@MoS₂). In this study, the scope of O-H bond activation is expanded through the investigation of the reactivity of various alcohols with differing p<i>K</i>_a values for the -OH proton. The reaction of (Cp*3Mo3S4)UCp* with stoichiometric amounts of methanol, phenol, 2,6-dichlorophenol, and nonafluoro-<i>tert</i>-butyl alcohol affords the corresponding mono-alkoxide species, (Cp*3Mo3S4)Cp*U(OR), <i>via</i> a uranium-metalloligand cooperative activation of the O-H bond. This observed reactivity is analogous to the O-H bond activation reported by (Cp*3Mo3S4)UCp* in the presence of water. However, addition of <i>tert</i>-butanol induces protonolysis of the Cp* ligand on uranium, resulting in the formation of a uranium tris-<i>tert</i>-butoxide cluster, (Cp*3Mo3S4)U(OtBu)3. Independent synthesis of (Cp*3Mo3S4)Cp*U(OtBu) was possible <i>via</i> an alternative pathway, eliminating sterics as a justification for the observed discrepancy in reactivity. These results offer insight into the role the -OH proton p<i>K</i>_a plays in dictating the mechanism of O-H bond activation of alcohols by the uranium-substituted thiomolybdate cluster.