Preparation and Reactions of Base-Free Bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium Oxide, Cp‘₂UO

Reduction of the uranium metallocene [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1), Cp‘2UCl2, in the presence of 2,2‘-bipyridyl and sodium naphthalene gives the dark green metallocene complex Cp‘2U(bipy) (6), which reacts with p-tolyl azide or pyridine-N-oxide to give Cp‘2UN(p-tolyl) (7) or Cp‘2U(O)(py) (8), respectively. The Lewis acid BPh3 precipitates Ph3B(py) and gives the base-free oxo Cp‘2UO (10), which crystallizes from pentane. The oxometallocene 10 behaves as a nucleophile with Me3SiX reagents, but it does not exhibit cycloaddition behavior with acetylenes, suggesting that the polar resonance structure Cp‘2U+−O- dominates the double-bond resonance structure Cp‘2UO.