Evidence for Uranium(VI/V) Redox Supported by 2,2'-Bipyridyl-6,6'-dicarboxylate.

The 2,2'-bipyridyl-6,6'-dicarboxylate ligand () has been shown in prior work to effectively capture the uranyl(VI) ion, UO, from aqueous solutions. However, the redox properties of the uranyl complex of this ligand have not been addressed despite the relevance of uranium-centered reduction to the nuclear fuel cycle and the presence of a bipyridyl core in , a motif long recognized for its ability to support redox chemistry. Here, the complex of UO () has been synthetically prepared and isolated under nonaqueous conditions for the study of its reductive chemical and electrochemical behavior. Spectrochemical titration data collected using decamethylcobaltocene (Cp*Co) as the reductant demonstrate that 1e reduction of is accessible, and companion near-infrared and infrared spectroscopic data, along with theoretical findings from density functional theory, provide evidence that supports the accessibility of the U(V) oxidation state. Data obtained for control ruthenium complexes of and related polypyridyl dicarboxylate ligands provide a counterpoint to these findings; ligand-centered reduction of in these control compounds occurs at potentials more negative than those measured for reduction of , further supporting the generation of uranium(V) in . Taken together, these results underscore the usefulness of as a ligand for actinyl ions and suggest that it could be useful for further studies of the reductive activation of these unique species.