A Direct Route to Bis(imido)uranium(V) Halides via Metathesis of Uranium Tetrachloride

Metathesis reactions between uranium tetrachloride and lithium 2,6-diisopropylphenylamide in the presence of 4,4′-dialkyl-2,2′-bipyridyl (R2bpy; R = Me, tBu) or triphenylphosphine oxide (tppo) appear to generate bis(imido)uranium(IV) in situ. These extremely reactive complexes abstract chloride from dichloromethane to generate U(NDipp)2Cl(R2bpy)2 or U(NDipp)2Cl(tppo)3 (Dipp = 2,6-iPr2C6H3). The preparation of the bromide and iodide analogues U(NDipp)2X(R2bpy)2 was achieved by addition of CH2X2 (X = Br, I) to the uranium(IV) solutions. The uranium(V) halides were characterized by X-ray crystallography and found to exhibit linear N–U–N units and short U–N bonds. Electrochemical measurements were made on the chloride bipyridine species, which reacts readily with iodine or ferrocenium to generate bis(imido)uranium(VI) cations.