Halide Effects in the Synthesis of Mixed Uranium(IV) Aryloxide-Halide Compounds

Several uranium(IV) aryloxide and mixed aryloxide-halide compounds of the formula UX(4)(-)(z)()(OAr)(z)() (X = Cl, Br, I; OAr = 2,6-di-tert-butylphenoxide; z = 2, 3, 4) have been prepared by the reaction of KOAr with the appropriate uranium tetrahalide in tetrahydrofuran (THF). The complex UI(4)(CH(3)CN)(4) reacts with 2 equiv of KOAr in THF to yield the compound I(2)U(OAr)(2) (1). The utility of this reaction is limited by the instability of UI(4)(CH(3)CN)(4) in THF, however, and isolated yields of the THF adduct of 1 do not exceed 50%. In contrast, UBr(4)(CH(3)CN)(4) is stable in THF solution and reacts with 2 equiv of KOAr to yield the dibromide, Br(2)U(OAr)(2)(THF) (4.THF), in 77% yield. Under identical reaction conditions, UCl(4) reacts to yield the complex [K(THF)(4)][UCl(3)(OAr)(2)] (5) in 68% yield. The uranium center in compound 5 is coordinated by two trans aryloxide ligands and three chloride ligands in a trigonal bipyramidal arrangement. Two chloride ligands of each unit are also coordinated to a potassium ion, forming an infinite chain in the lattice. Compounds 1 and 5 will further react with 1 equiv of KOAr to yield the compounds XU(OAr)(3) (2, X = I; 6, X = Cl). Both UI(4)(CH(3)CN)(4) and UCl(4) will react with a 4.2 equiv of KOAr to yield the previously characterized compound U(OAr)(4) (3). The stability of the mixed aryloxide-halide uranium complexes toward ligand redistribution reactions has been investigated.