Trimethylsilylcyclopentadienyl (Cp′) Uranium Chemistry: Synthetic and Structural Studies of Cp′4U and Cp′3UX (X = Cl, I, Me)

Cp′4U (Cp′ = C5H4SiMe3) was synthesized from: (a) KCp′ and [Cp′3U(THF)][BPh4]; (b) Cp′3U and Cp′2Pb; and (c) [K(2.2.2-cryptand)][Cp′4U] and AgBPh4. Identified by X-ray crystallography as a rare example of a structurally-characterized tetrakis(cyclopentadienyl)U(IV) complex. For comparison, the corresponding Th complex, Cp′4Th, was isolated from the direct combination of ThBr4(THF)4 with excess KCp′. During the preparation of Cp′3UMe, the precursor of the [Cp′3U(THF)][BPh4] reagent used above, it was discovered that the reaction of Cp′3UCl and MeLi gives a mixture of Cp′3UMe and Cp′3UCl that can co-crystallize better than Cp′3UMe in pure form. The Cp′3UMe/Cp′3UCl mixture forms single crystals suitable for X-ray crystallography and provides a new way to characterize the oil, Cp′3UMe. Cp′3UCl and Cp′3UI were also crystallographically characterized for comparison with the Cp′3UMe/Cp′3UCl crystals.