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

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).