Straightforward and efficient oxidation of tris(aryloxide) and tris(amide) uranium(III) complexes using copper(I) halide reagents

Reaction of the trivalent uranium complex U(O-2,6-tBu2C6H3)3(THF) (4) with copper(I) iodide affords the corresponding uranium(IV) mixed iodide–aryloxide complex (I)U(O-2,6-tBu2C6H3)3(THF) (5). The oxidative functionalization protocol can also be extended to the synthesis of (Cl)U[N(SiMe3)2]3 (7) from the reaction of the tris(amide) uranium(III) complex U[N(SiMe3)2]3 (6) with copper(I) chloride. These represent the first examples of Cu-based oxidative functionalization of simple trivalent uranium coordination complexes supported by non-metallocene ligand frameworks. With several advantages over existing oxidation methods for uranium tris(aryloxide) and tris(amide) complexes, this Cu-based procedure promises to be a useful and versatile synthetic protocol for uranium chemistry. The X-ray crystal structure of (I)U(O-2,6-tBu2C6H3)3(THF) (5) is also reported and represents a rare example of a structurally characterized 5-coordinate uranium aryloxide complex. In the solid-state, complex 5 adopts a distorted square pyramidal geometry about the uranium atom, with the iodide ligand occupying the axial position and the THF and three 2,6-di-tert-butylphenoxide ligands occupying the sites of the square pyramid base.