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 UCI4, a more accessible uranium starting material that can be prepared from commercially available uranium oxides. UCI3(THF)(2) (1), UBr3(THF)(4) (2), and UI3(THF)(4) (3) were prepared by single-pot reductions from UCI4 using KH and KC 8 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 HCI 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 H-1 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.

Automated summary

Low-valent uranium coordination chemistry heavily relies on trivalent starting materials, traditionally prepared from uranium turnings. This study presents convenient syntheses of UI3(THF)(4) and UBr3(THF)(4) from UCI4, a more accessible uranium starting material derived from commercially available uranium oxides. The trivalent uranium halide complexes were successfully isolated in high crystalline yields and showed significant THF loss when exposed to vacuum, offering a new route for researchers without access to uranium turnings.