Oxidative Addition to U(V)−U(V) Dimers: Facile Routes to Uranium(VI) Bis(imido) Complexes

The ability of dimeric bis(imido) uranium(V) complexes with the general formula [U(NtBu)2(Y)(tBu2bpy)]2 (Y = I (1), SPh (2); tBu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridyl) to behave as two-electron reducing agents was examined with I2, AgX (X = Cl, Br), PhEEPh (E = S, Se, Te), and chalcogen (O, S, Se) atom transfer reagents. The addition of I2 and AgX to 1 leads to the formation of uranium(VI) dihalide complexes with the general formula U(NtBu)2(I)(X)(tBu2bpy) (X = I (3), Cl (4), Br (5)). Complexes 1 and 2 can also reduce PhEEPh to generate uranium(VI) complexes with the general formula U(NtBu)2(X)(EPh)(tBu2bpy) (X = I, E = S (6), Se (8), Te (10); X = SPh, E = S (7), Se (12)). These unsymmetrical complexes appear to be in equilibrium with the uranium(VI) complexes U(NtBu)2(X)2(tBu2bpy) and U(NtBu)2(EPh)2(tBu2bpy) (E = Se (9), Te (11)) and suggest that both U−I and U−E bonds possess a labile nature in bis(imido) uranium(VI) complexes. Complex 1 also reacts as a two-electron reductant toward chalcogen atom transfer reagents such as 4-methylmorpholine N-oxide, S8, and Se to produce dimeric bis(imido) uranium(VI) complexes with the general formula [U(NtBu)2(I)(tBu2bpy)]2(μ-E) (E = O (13), S (14), Se (15)) and [U(NtBu)2(I)(tBu2bpy)]2(μ-η2:η2-E4) (E = S (16), Se (17)). Density functional theory studies performed on a model complex of 13 indicate the presence of multiple bonding in the bridging U−O bond.