Convenient Syntheses of Trivalent Uranium Halide Starting Materials without Uranium Metal

Abstract

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.