Trimethylsilylcyclopentadienyl (Cp) Uranium Chemistry: Synthetic and Structural Studies of Cp4U and Cp3UX (X = Cl, I, Me)

Cp4U (Cp = C5H4SiMe3) was synthesized from: (a) KCp and [Cp3U(THF)][BPh4]; (b) Cp3U and Cp2Pb; and (c) [K(2.2.2-cryptand)][Cp4U] and AgBPh4. The compound was identified by X-ray crystallography as a rare example of a structurally-characterized tetrakis(cyclopentadienyl)U-IV complex. For comparison, the corresponding Th complex, Cp4Th, was isolated from the direct combination of ThBr4(THF)(4) with excess KCp. During the preparation of Cp3UMe, the precursor of the [Cp3U(THF)][BPh4] reagent used above, it was discovered that the reaction of Cp3UCl and MeLi gives a mixture of Cp3UMe and Cp3UCl that can co-crystallize better than Cp3UMe in pure form. The Cp3UMe/Cp3UCl mixture forms single crystals suitable for X-ray crystallography and provides a new way to characterize the oil, Cp3UMe. Cp3UCl and Cp3UI were also crystallographically characterized for comparison with the Cp3UMe/Cp3UCl crystals.