Expanding the Chemistry of Molecular U 2+ Complexes: Synthesis, Characterization, and Reactivity of the {[C 5 H 3 (SiMe 3 ) 2 ] 3 U} − Anion

The synthesis of new molecular complexes of U 2+ has been pursued to make comparisons in structure, physical properties, and reactivity with the first U 2+ complex, [K(2.2.2‐cryptand)][Cp′ 3 U], 1 (Cp′=C 5 H 4 SiMe 3 ). Reduction of Cp′′ 3 U [Cp′′=C 5 H 3 (SiMe 3 ) 2 ] with KC 8 in the presence of 2.2.2‐cryptand or 18‐crown‐6 generates [K(2.2.2‐cryptand)][Cp′′ 3 U], 2‐K(crypt) , or [K(18‐crown‐6)(THF) 2 ][Cp′′ 3 U], 2‐K(18c6) , respectively. The UV/Vis spectra of 2‐K and 1 are similar, and they are much more intense than those of U 3+ analogues. Variable temperature magnetic susceptibility data for 1 and 2‐K(crypt) reveal lower room temperature χ M T values relative to the experimental values for the 5f 3 U 3+ precursors. Stability studies monitored by UV/Vis spectroscopy show that 2‐K(crypt) and 2‐K(18c6) have t 1/2 values of 20 and 15 h at room temperature, respectively, vs. 1.5 h for 1 . Complex 2‐K(18c6) reacts with H 2 or PhSiH 3 to form the uranium hydride, [K(18‐crown‐6)(THF) 2 ][Cp′′ 3 UH], 3 . Complexes 1 and 2‐K(18c6) both reduce cyclooctatetraene to form uranocene, (C 8 H 8 ) 2 U, as well as the U 3+ byproducts [K(2.2.2‐cryptand)][Cp′ 4 U], 4 , and Cp′′ 3 U, respectively.