Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

Addition of the potassium salt of the bulky tetra(isopropyl)cyclopentadienyl (CpiPr4) ligand to UI3(1,4-dioxane)1.5 results in the formation of the bent metallocene uranium(III) complex (CpiPr4)2UI (1), which is then used to obtain the uranium(IV) and uranium(III) dihalides (CpiPr4)2UIVX2 (2-X) and [cation][(CpiPr4)2UIIIX2] (3-X, [cation]+ = [Cp*2Co]+, [Et4N]+, or [Me4N]+) as mononuclear, donor-free complexes, for X– = F–, Cl–, Br–, and I–. Interestingly, reaction of 1 with chloride and cyanide salts of alkali metal ions leads to isolation of the chloride- and cyanide-bridged coordination solids [(CpiPr4)2U(μ-Cl)2Cs]n (4-Cl) and [(CpiPr4)2U(μ-CN)2Na(OEt2)2]n (4-CN). Abstraction of the iodide ligand from 1 further enables isolation of the “base-free” metallocenium cation salt [(CpiPr4)2U][B(C6F5)4] (5) and its DME adduct [(CpiPr4)2U(DME)][B(C6F5)4] (5-DME). Solid-state structures of all of the compounds, determined by X-ray crystallography, facilitate a detailed analysis of the effect of changing oxidation...