Activation\nand Functionalization of the Uranyl Ion\nby Electrochemical Reduction

Interconversion\nof the oxidation states of uranium enables\nseparations\nand reactivity schemes involving this element and contributes to technologies\nfor recycling of spent nuclear fuels. The redox behaviors of uranium\nspecies impact these processes, but use of electrochemical methods\nto drive reactions of molecular uranium complexes and to obtain molecular\ninsights into the outcomes of electrode-driven reactions has received\nfar less attention than it deserves. Here, we show that electro-reduction\nof the uranyl ion (UO<sub>2</sub><sup>2+</sup>) can be used to promote\nstepwise functionalization of the typically unreactive oxo groups\nwith exogenous triphenylborane (BPh<sub>3</sub>) serving as a moderate\nelectrophile, avoiding the conventional requirement for a chemical\nreductant. Parallel electroanalytical, spectrochemical, and chemical\nreactivity studies, supported by spectroscopic findings and structural\ndata from X-ray diffraction analysis on key reduced and borylated\nproducts, demonstrate that our electrochemical approach largely avoids\nundesired cross reactions and disproportionation pathways; these usually\nimpact the multicomponent systems needed for uranyl functionalization\nchemistry. Joint computational studies have been used to map the changes\nassociated with U–O activation and to quantify the free energy\ndifferences related to key reactions. Taken together, the results\nsuggest that electrochemical methods can be used for selective interconversion\nof molecular actinide species, reminiscent of methods commonly employed\nin transition metal redox catalysis.