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.