Synthesis and Reactivity of the Imido Analogues of the Uranyl Ion

Addition of 1.5 equiv of I2 to a THF solution of UI3(THF)4, containing either 6 equiv of tBuNH2 or
2 equiv of RNH2 (R = Ph, 3,5-(CF3)2C6H3, 2,6-(iPr)2C6H3) and 4 equiv of NEt3, generates orange solutions
containing U(NtBu)2I2(THF)2 (1) or U(NAr)2I2(THF)3 (Ar = Ph, 2; 3,5-(CF3)2C6H3, 3; 2,6-(iPr)2C6H3, 4),
respectively, all of which can be isolated in good yields. Alternatively, 1 can be prepared by reaction of
uranium metal with 3 equiv of I2 and 6 equiv of tBuNH2, also in good yield. Complexes 1−4 have been
characterized by X-ray crystallography, and each of these complexes exhibits linear N−U−N linkages and
short U−N bonds. Using density functional theory simulations of complexes 1 and 2, two triple bonds
between the metal center and the nitrogen ligands were identified. Complexes 1 and 2 readily react with
neutral Lewis bases such as pyridine or Ph3PO to form U(NR)2I2(L)2 (R = tBu, L = py, 5; Ph3PO, 7; R =
Ph, L = py, 6; Ph3PO, 8), and with PMe3 to form U(NR)2I2(THF)(PMe3)2 (R = tBu, 9; Ph, 10). The solid-state molecular structures of 5, 7, and 9 have been determined by X-ray crystallography, and these
complexes, like their parent compounds, exhibit linear N−U−N angles and short U−N bonds. Complexes
1 and 2 also react with AgOTf in CH2Cl2, forming U(NR)2(OTf)2(THF)3 (R = tBu, 11; Ph, 12) after
recrystallization from THF. Crystals of 12 grown from CH2Cl2 were found to contain a dimer, [U(NPh)2(OTf)2(THF)2]2, a complex possessing bridging triflate groups.