Synthesis, characterization, and structures of uranium(III) N, N-dimethylaminodiboranates

The reaction of UCl₄ with sodium N,N-dimethylaminodiboranate, Na(H₃BNMe₂BH₃), in diethyl ether affords the uranium(III) product U(H₃BNMe₂BH₃)₃, which has been crystallized as two different structural isomers from pentane and toluene, respectively. The isomer crystallized from pentane is a polymer in which each uranium center is bonded to three chelating H₃BNMe ₂BH₃ (DMADB) ligands and to one hydrogen atom from a neighboring molecule so as to form an intermolecular BiHiU bridge; each uranium center is coordinated to 13 hydrogen atoms. The isomer crystallized from toluene is also polymeric, but the uranium atoms are coordinated by two chelating DMADB ligands and two bridging DMADB ligands bound in a U(³H-H ₃BNMe₂BH₃-³H)U fashion, so that each uranium atom is 14-coordinate. When the reaction of UCl₄ with Na(H₃BNMe₂BH₃) is conducted in tetrahydrofuran (thf) or 1,2-dimethoxyethane (dme), the adducts U(H₃BNMe ₂BH₃)₃(thf) and U(H₃BNMe ₂BH₃)₃(dme) are obtained. The rate of reduction from U^IV to U^III is correlated with the donor ability of the solvent, the relative rates being Et₂O > thf > dme. The addition of trimethylphosphine to U(H₃BNMe₂BH ₃)₃(thf) generates U(H₃BNMe₂BH ₃)₃(PMe₃)₂. This compound slowly decomposes at room temperature over several months to yield the new borane PMe₃BH₂NMe₂BH₃,(N,N-dimethylamido) pentahydro(trimethylphosphine)diboron. Single crystal X-ray diffraction studies, ¹H and ¹¹B NMR spectra, IR data, and field ionization mass spectra for the uranium complexes are reported.