A Convenient Entry into Trivalent Actinide Chemistry: Synthesis and Characterization of AnI3(THF)4 and An[N(SiMe3)2]3 (An = U, Np, Pu)

Abstract

The reaction of excess, oxide-free amalgamated uranium metal turnings with elemental iodine or bromine in coordinating solvents at 0{degree}C provides dark purple UI{sub 3}(THF){sub 4}(1), royal blue UBr{sub 3}(THF){sub 4} (2), purple UI{sub 3}(dme){sub 2} (3), or jet black UI{sub 3}(py){sub 4} (4) in 65-80% isolated yield (THF = tetrahydofuran, dme = 1,2-dimethoxyethane, py = pyridine). Neptunium and plutonium metal also react cleanly with elemental iodine in aprotic coordinating solvents to give yellow-orange NpI{sub 3}(THF){sub 4} (5), off-white PuI{sub 3}(THF){sub 4} (6), and gray PuI{sub 3}(py){sub 4} (7) in 80-90% isolated yields. These organic-solvent-soluble Lewis base adducts of early actinide trihalides are precursors to a variety of inorganic and organometallic actinide complexes. Reaction of AnI{sub 3}(THF){sub 4} complexes (U, Np, Pu) 1, 5, and 6 in THF solution with 3 equiv of sodium bis(trimethylsilyl)amide provides the volatile, solvent-free tris(silylamide) complexes An[N(SiMe{sub 3}){sub 2}]{sub 3} [An = U (8), Np (9), Pu (10)] in 80-90% yields. The neptunium and plutonium silylamides are the first examples of homoleptic amido complexes of the transuranic elements. Compounds 1-10 have been fully characterized by variable-temperature proton NMR, IR, UV/vis/near-IR, thermal gravimetric, and elemental analyses. Single-crystal X-ray diffraction data for 1 revealed a pentagonal bipyramidal coordinationmore » geometry about the central uranium atom with two axial iodide ligands (U-I = 3.111(2) {Angstrom} (average)) and one equatorial iodide ligand (U-I = 3.167(2) {Angstrom}). All four THF ligands lie in the equatorial plane with an average U-O distance of 2.52(1) {Angstrom}. Crystal data for 1 (at 23{degree}C): monoclinic space group P2{sub 1}/c, with a = 8.750(3) {Angstrom}, b = 16.706(16) {Angstrom}, c = 17.697(7) {Angstrom}, {beta} = 93.64(3){sup o}, V = 2582 {Angstrom}{sup 3}, d{sub calc} = 2.33 g cm{sup {minus}3}, Z = 4.« less