Reactivity of dicyclopentadienylbis(diethylamido)uranium(IV). Reactions with carboxylic and thiocarboxylic acids

The reaction of Cp2U(NEt2)2 with carboxylic and thiocarboxylic acids produced complexes of the type Cp2U(XYCR)2 (X = Y = O, R = Me, Ph, t-Bu; X = O, Y = S, R = Me, Ph). Solubility properties of the acetate and benzoate derivatives indicate polymeric behavior, whereas molecular weight measurements show that the pivalate complex is dimeric and the thiobenzoate compound is monomeric. The infrared spectra of all the complexes indicate eta5-cyclopentadienyl bonding and bidentate, chelating and/or bridging, carboxylate moieties. Assuming that the monomeric Cp2U(OSCPh)2 exhibits the expected pseudo-cis-octahedral geometry, it is shown that the variable-temperature 1H NMR spectra of the molecule is only compatible with a combination of metal-centered rearrangement and C-Ph bond rotation. The simple and temperature-invariant nature of the spectrum for Cp2U(O2CCMe3)2 implies a symmetrical dimeric structure, and a possibility for this is proposed