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((NBu)-Bu-t)(2)(Y)((t)Bu(2)bpy)](2) (Y = I (1), SPh (2); (t)Bu(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridyl) to behave as two-electron reducing agents was examined with I-2, AgX (X = Cl, Br), PhEEPh (E = S, Se, Te), and chalcogen (O, S, Se) atom transfer reagents. The addition of I-2 and AgX to 1 leads to the formation of uranium(VI) dihalide complexes with the general formula U((NBu)-Bu-t)(2)(I)(X)((t)Bu(2)bpy) (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((NBu)-Bu-t)(2)(X)(EPh)((t)Bu(2)bpy) (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((NBu)-Bu-t)(2)(X)(2)((t)Bu(2)bpy) and U((t)'Bu)(2)(EPh)(2)((t)Bu(2)bpy) (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, S-8, and Se to produce dimeric bis(imido) uranium(VI) complexes with the general formula [U((NBu)-Bu-t)(2)(I)((t)Bu(2)bpy)](2)(mu-E) (E = O (13), S (14), Se (15)) and [U((NBu)-Bu-t)(2)(I)((t)Bu(2)bpy)](2)(mu-eta(2):eta E-2-(4)) (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.