Expanding the Chemistry of Molecular U2+ Complexes: Synthesis, Characterization, and Reactivity of the {[C5H3(SiMe3)2]3U}− Anion

The synthesis of new molecular complexes of U2+ has been pursued to make comparisons in structure, physical properties, and reactivity with the first U2+ complex, [K(2.2.2-cryptand)][Cp′3U], 1 (Cp′=C5H4SiMe3). Reduction of Cp′′3U [Cp′′=C5H3(SiMe3)2] with KC8 in the presence of 2.2.2-cryptand or 18-crown-6 generates [K(2.2.2-cryptand)][Cp′′3U], 2-K(crypt), or [K(18-crown-6)(THF)2][Cp′′3U], 2-K(18c6), respectively. The UV/Vis spectra of 2-K and 1 are similar, and they are much more intense than those of U3+ analogues. Variable temperature magnetic susceptibility data for 1 and 2-K(crypt) reveal lower room temperature χMT values relative to the experimental values for the 5f3 U3+ precursors. Stability studies monitored by UV/Vis spectroscopy show that 2-K(crypt) and 2-K(18c6) have t1/2 values of 20 and 15 h at room temperature, respectively, vs. 1.5 h for 1. Complex 2-K(18c6) reacts with H2 or PhSiH3 to form the uranium hydride, [K(18-crown-6)(THF)2][Cp′′3UH], 3. Complexes 1 and 2-K(18c6) both reduce cyclooctatetraene to form uranocene, (C8H8)2U, as well as the U3+ byproducts [K(2.2.2-cryptand)][Cp′4U], 4, and Cp′′3U, respectively.