A General and Modular Synthesis of Monoimidouranium(IV) Dihalides

The conproportionation reaction between the dimeric diimidouranium(V) species [U(NtBu)2(I)(tBu2bpy)]2 (tBu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridyl) and UI3(THF)4 in the presence of additional tBu2bpy yields U(NtBu)(I)2(tBu2bpy)(THF)2 (2), an unprecedented example of a monoimidouranium(IV) dihalide complex. The general synthesis of this family of uranium(IV) derivatives can be achieved more readily by adding 2 equiv of MN(H)R (M = Li, K; R = tBu, 2,6-iPrC6H3, 2-tBuC6H4) to UX4 in the presence of coordinating Lewis bases to give complexes with the general formula U(NR)(X)2(L)n (X = Cl, I; L = tBu2bpy, n = 1; L = THF, n = 2). The complexes were characterized by 1H NMR spectroscopy and single-crystal X-ray diffraction analysis of compounds 2 and {U[N(2,6-iPrC6H3)](Cl)2(THF)2}2 (4). (The X-ray structures of 5 and 6 are reported in the Supporting Information.)