Electrochemical Activation and Functionalization of the Uranyl Ion

Interconversion of the oxidation states of uranium enables separations and reactivity schemes involving this element and contributes to technologies for recycling of spent nuclear fuels. The redox behaviors of uranium species impact these processes, but use of electrochemical methods to drive reactions of well-defined precursors and to obtain molecular insights into the outcomes has received less attention than it deserves. Here, we show that electro-reduction of the uranyl ion (UO22+) can be used to promote stepwise functionalization of the typically unreactive oxo groups with exogenous triphenylborane (BPh3) serving as a moderate electrophile. Parallel electroanalytical, spectrochemical, and chemical reactivity studies, supported by spectroscopic findings and structural data from X-ray diffraction analysis on key reduced and borylated products, demonstrate that our electrochemical approach largely avoids undesired cross reactions and disproportionation pathways; these conventionally impact the multicomponent systems needed for uranyl functionalization chemistry. Joint computational studies have been used to map the mechanistic pathways involved in this U–O activation, and to quantify free energy changes associated with key reactions. Taken together, the results suggest that electrochemical methods can be used for selective interconversion of molecular actinide species, reminiscent of methods commonly employed in transition metal redox catalysis.