Uranium(III)/(IV) nitrile adducts including UI4(NCPh)4, a synthetically useful uranium(IV) complex

The synthesis of complexes used to elucidate an understanding of fundamental An(III) and An(IV) coordination chemistry requires the development of suitable organic-soluble precursors. The reaction of oxide-free uranium metal turnings with 1.3 equivalents of elemental iodine in acetonitrile provided the U(III)/U(IV) complex salt, [U(N=CMe)(9)][Ul(6)][I] (1), in which the U(III) cation is surrounded by nine acetonitrile molecules in a tricapped trigonal prismatic arrangement, a [Ul(6)](2-) counterion, and a noncoordinating iodide. The U-N distances for the prismatic and capping nitrogens are 2.55(3) and 2.71(5) A, respectively. The same reaction performed in benzonitrile afforded crystalline Ul(4)(N=CPh)(4) (3) in 78% isolated yield. In the solid state, 3 shows an eight-coordinate U(IV) atom in a puckered square antiprismatic geometry with U-N and U-I distances of 2.56(1) and 3.027(1) angstrom, respectively. This benzonitrile Ul(4) adduct is a versatile U(IV) synthon that is soluble in methylene chloride, benzonitrile, and tetrahydrofuran, and moderately soluble in toluene and benzene, but decomposes in benzonitrile at 198 degrees C to [Ul(N=CPh)(8)][UI](6) (4), a U(III)/U(IV) salt analogous to 1. A toluene slurry of 3 treated with 2.2 equiv of Cp*(MgClTHF)-T-. (Cp* = pentamethylcyclopentadienide) provided CP*(2)Ul(2)(N=CPh) (5) in low yields. Single-crystal X-ray structure determination shows that the iodide ligands in 5 are in a rare cis configuration with an acute I-U-I angle of 83.16(7)degrees. Treatment of a methylene chloride solution of 3 with KTp* (Tp* = hydridotris(3,5-dimethylpyrazolylborate)) formed green Tp*UI3 (6) which was converted to yellow Tp*Ul(3)(N=CMe) (7) by rinsing with acetonitrile. Addition of 2.2 equiv of KTp* to a toluene solution of 3 followed by heating at 95 degrees C, filtration, and crystallization led to the isolation of the dinuclear species [Tp*Ul(dmpZ)](2)[mu-O] (9) (dmpz = 3,5-dimethylpyrazolide), presumably formed by hydrolytic cleavage of excess KTp* by adventitious water. The Tp* complexes 6, 7, and 9 were characterized by single-crystal X-ray diffraction, NMR, FT-IR, and optical absorbance spectroscopies.