Preparation and reactions of base-free bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium oxide, Cp'2UO

Reduction of the uranium metallocene [eta(5)-1,2,4-(Me3C)(3)C5H2](2)UCl2 (1), CP'2UCl2, in the presence of 2,2'-bipyridyl and sodium naphthalene gives the dark green metallocene complex CP'U-2(bipy) (6), which reacts with p-tolyl azide or pyridine-N-oxide to give CP'U-2=N(p-tolyl) (7) or CP'U-2(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'U-2(+)-O- dominates the double-bond resonance structure Cp'U-2=O.