Synthesis of a Phosphorano-Stabilized U(IV)-Carbene via One-Electron Oxidation of a U(III)-Ylide Adduct

Addition of the Wittig reagent Ph3PCH2 to the U(III) tris(amide) U(NR2)3 (R = SiMe3) generates a mixture of products from which the U(IV) complex UCHPPh3(NR2)3 (2) can be obtained. Complex 2 features a short UC bond and represents a rare example of a uranium carbene. In solution, 2 exists in equilibrium with the U(IV) metallacycle U(CH2SiMe2NR)(NR2)2 and free Ph3PCH2. Measurement of this equilibrium as a function of temperature provides ΔHrxn = 11 kcal/mol and ΔSrxn = 31 eu. Additionally, the electronic structure of the UC bond was investigated using DFT analysis.