Tuning Reactivity at Uranium through Heterometal Substitution in a Redox-active Thiomolybdate Metalloligand

Abstract

Redox-active metalloligands are advantageous for their ability to serve as electron reservoirs to facilitate multielectron transformations at metal centers. However, strategies for tuning their electronic properties remain limited, and investigation into how this impacts reactivity at the coordinated metal center is understudied, particularly in the field of actinide chemistry. Isolation of a heterometal-substituted uranium-bound thiomolybdate assembly was performed using a pre-assembled “UMo2” complex, Cp*3(UI2)Mo2S4, which serves as a platform to synthesize the zirconium-substituted cluster, (Cp*3ZrMo2S4)Cp*UCl2. Further reduction affords the fully reduced cluster, (Cp*3ZrMo2S4)Cp*U, which was used in comparative small molecule activation studies with its homometallic analogue, (Cp*3Mo3S4)Cp*U. The reactivity of the fully reduced cluster with azobenzene was investigated, resulting in the formation a high-valent uranium bis-imido complex. Bond metric analysis of the Zr-doped species reveals that heterometal substitution forces localization of oxidation at the uranium center, generating a UVI-bis(imido) species, (Cp*3ZrMo2S4)Cp*U(NPh)2. Furthermore, addition of elemental sulfur to (Cp*3ZrMo2S4)Cp*U generates a unique disulfide-bridged product, (Cp*3ZrMo2S4)Cp*U(μ2-S2)2, where significant rearrangement of the assembly occurs due to the increased nucleophilicity of the sulfur sites coordinated to the heterometal. This contrasts with the reactivity of the all-molybdenum analogue and elemental sulfur which favors decomposition under analogous conditions. These results indicate that tuning the electronic structure of redox-active thiomolybdate metalloligands through heterometal substitution serves as an effective strategy for modulating multielectron reactivity at uranium.