A Homoleptic Uranium(III) Tris(aryl) Complex.

The reaction of 3 equiv of Li-C6 H3 -2,6-(C6 H4 -4-t Bu)2 (Terph-Li) with UI3 (1,4-dioxane)1.5 led to the formation of the homoleptic uranium(III) tris(aryl) complex (Terph)3 U (1). The U-C bonds are reactive: treatment with excess i PrN═C═Ni Pr yielded the double-insertion product [TerphC(Ni Pr)2 ]2 U(Terph) (2). Complexes 1 and 2 were characterized by X-ray crystallography, which showed that the U-C bond length in 2 (2.624(4) Å) is ∼0.1 Å longer than the average U-C bond length in 1 (2.522(2) Å). Thermal decomposition of 1 yielded Terph-H as the only identifiable product; the process is unimolecular with activation parameters ΔH⧧ = 21.5 ± 0.3 kcal/mol and ΔS⧧ = -7.5 ± 0.8 cal·mol-1 K-1 , consistent with intramolecular proton abstraction. The protonolysis chemistry of 1 was also explored, which led to the uranium(IV) alkoxide complex U(OCPh3 )4 (DME) (3·DME).