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).