Structure of Uranium(V) Methyl and Uranium(IV) Ylide Complexes

Syntheses of rare examples of U(V) methyl and U(IV) ylide complexes are reported. Reaction of the previously reported U(IV) imido complex [(C5Me5)2U(py)(NMes)] (py = pyridine, and Mes = 2,4,6-Me3C6H2) with CuI forms the U(V) complex [(C5Me5)2U(I)(NMes)]. Reaction of the iodo complex with MgMe2 produces the methyl complex [(C5Me5)2U(CH3)(NMes)]. The methyl complex was reacted with CH2PPh3, surprisingly forming [(C5Me5)2U(CH2PPh3)(NMes)], a U(IV) ylide. This is formed from a disproportionation of a transient U(V) carbene, leading to the U(IV) ylide and a U(VI) bis(imido) complex, [(C5Me5)2U(NMes)2]. These complexes were characterized using spectroscopic methods (nuclear magnetic resonance, infrared, and ultraviolet–visible–nean infrared), SQUID magnetometry, and X-ray crystallography, and density functional theory calculations are used to compare the U(V) methyl with the targeted U(V) carbene ligands.