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'-dialky1-2,2'-bipyridyl (R(2)bpy; R = Me, Bu-t) 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)(2)Cl(R(2)bpy)(2) or U(NDipp)(2)Cl-(tppo)(3) (Dipp = 2,6-(Pr2C6H3)-Pr-i). The preparation of the bromide and iodide analogues U(NDipp)(2)X(R(2)bpy)(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.