Convenient Syntheses of Trivalent Uranium Halide Starting Materials without Uranium Metal

Low-valent uranium coordination chemistry continues to rely heavily on access to trivalent starting materials, but these reagents are typically prepared from uranium turnings, which are becoming increasingly difficult to acquire. Here we report convenient syntheses of UI₃(THF)₄ (THF = tetrahydrofuran) and UBr₃(THF)₄ from UCl₄, a more accessible uranium starting material that can be prepared from commercially available uranium oxides. UCl₃(THF)₂ (1), UBr₃(THF)₄ (2), and UI₃(THF)₄ (3) were prepared by single-pot reductions from UCl₄ using KH and KC₈ and converted to 2 or 3 by halide exchange with the corresponding Me₃SiX (where X = Br or I). Reduction of UI₄(Et₂O)₂ (4; Et₂O = diethyl ether) and UI₄(1,4-dioxane)₂ (5) was also shown to cleanly yield 3. Complex 1 was also synthesized separately by the addition of anhydrous HCl to U(BH₄)₃(THF)₂, which was prepared by thermal reduction of U(BH₄)₄. All three trivalent uranium halide complexes were isolated in high crystalline yields (typically 85-99%) and their formulations were confirmed by single-crystal X-ray diffraction, elemental analysis, and ¹H NMR and IR spectroscopy. Elemental analysis conducted on triplicate samples of 1-3 exposed to vacuum for different time intervals revealed significant THF loss for all three complexes in as little as 15 min. Overall, these results offer expedient entry into low-valent uranium chemistry for researchers lacking access to uranium turnings.