Delivery of a Masked Uranium(II) by an Oxide-Bridged Diuranium(III) Complex

Oxide is an attractive linker for building polymetallic complexes that provide molecular models for metal oxide activity, but studies of these systems are limited to metals in high oxidation states. Herein, we synthesized and characterized the molecular and electronic structure of diuranium bridged U-III/U-IV and U-III/U-III complexes. Reactivity studies of these complexes revealed that the U-O bond is easily broken upon addition of N-heterocycles resulting in the delivery of a formal equivalent of U-III and U-II, respectively, along with the uranium(IV) terminal-oxo coproduct. In particular, the U-III/U-III oxide complex effects the reductive coupling of pyridine and two-electron reduction of 4,4 '-bipyridine affording unique examples of diuranium(III) complexes bridged by N-heterocyclic redox-active ligands. These results provide insight into the chemistry of low oxidation state metal oxides and demonstrate the use of oxo-bridged U-III/U-III complexes as a strategy to explore U-II reactivity.