A Homoleptic Uranium(III) Tris(aryl) Complex

Abstract

The reaction of 3 equiv of Li-C₆H₃-2,6-(C₆H₄-4-^tBu)₂ (Terph-Li) with UI₃(1,4-dioxane)_1.5 led to the formation of the homoleptic uranium(III) tris(aryl) complex (Terph)₃U (1). The U-C bonds are reactive: treatment with excess ⁱPrN═C═NⁱPr yielded the double-insertion product [TerphC(NⁱPr)₂]₂U(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).