Lawrence Berkeley National Laboratory

Reduction of the uranium metallocene, [eta5-1,2,4-(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-tolylazide or pyridine-N-oxide to give Cp'2U=N(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'2U=O.