μ-η6,η6-Arene-Bridged Diuranium Hexakisketimide Complexes Isolable in Two States of Charge

Diuranium mu-eta(6),eta(6)-arene complexes supported by ketimide ligands were synthesized and characterized. Disodium or dipotassium salts of the formula M-2(mu-eta(6),eta(6)-arene)[U(NC(t)BuMes)(3)](2) (M = Na or K, Mes = 2,4,6-C6H2Me3) and monopotassium salts of the formula K(mu-eta(6),eta(6)-arene)[U(NC(t)BuMes)(3)](2) (arene = naphthalene, biphenyl, trans-stilbene, or p-terphenyl) were both observed. Two different salts of the monoanionic, toluene-bridged complexes are also described. Density functional theory calculations have been employed to illuminate the electronic structure of the mu-eta(6),eta(6)-arene diuranium complexes and to facilitate the comparison with related transition-metal systems, in particular (mu-eta(6),eta(6)-C6H6)[VCp](2). It was found that the mu-eta(6),eta(6)-arene diuranium complexes were isolobal with (mu-eta(6),eta(6)-C6H6)[VCp](2) and that the principal arene-binding interaction was a pair of delta bonds (total of 4e) involving both metals and the arene lowest unoccupied molecular orbital. Reactivity studies have been carried out with the mono- and dianionic mu-eta(6),eta(6)-arene diuranium complexes, revealing contrasting modes of redox chemistry as a function of the system's state of charge.