Ligand-Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media.

Reduction of uranyl(VI) to U and to U is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U O (dpaea)] complex is readily converted into the cis-boroxide U species via diborane-mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na S O , a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a water-insoluble trinuclear U oxo-hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well-defined molecular U species in aqueous conditions.