High-Valent Uranium Alkyls: Evidence for the Formation of U^VI(CH₂SiMe₃)₆

Oxidation of [Li(DME)₃][U(CH₂SiMe₃)₅] with 0.5 equiv of I₂, followed by immediate addition of LiCH₂SiMe₃, affords the high-valent homoleptic U(V) alkyl complex [Li(THF)₄][U(CH₂SiMe₃)₆] (1) in 82% yield. In the solid-state, 1 adopts an octahedral geometry as shown by X-ray crystallographic analysis. Addition of 2 equiv of tert-butanol to [Li(DME)₃][U(CH₂SiMe₃)₅] generates the heteroleptic U(IV) complex [Li(DME)₃][U(O^tBu)₂(CH₂SiMe₃)₃] (2) in high yield. Treatment of 2 with AgOTf fails to produce a U(V) derivative, but instead affords the U(IV) complex (Me₃SiCH₂)Ag(μ-CH₂SiMe₃)U(CH₂SiMe₃)(O^tBu)₂(DME) (3) in 64% yield. Complex 3 has been characterized by X-ray crystallography and is marked by a uranium–silver bond. In contrast, oxidation of 2 can be achieved via reaction with 0.5 equiv of Me₃NO, producing the heteroleptic U(V) complex [Li(DME)₃][U(O^tBu)₂(CH₂SiMe₃)₄] (4) in moderate yield. We have also attempted the one-electron oxidation of complex 1. Thus, oxidation of 1 with U(O^tBu)₆ results in formation of a rare U(VI) alkyl complex, U(CH₂SiMe₃)₆ (6), which is only stable below −25 °C. Additionally, the electronic properties of 1–4 have been assessed by SQUID magnetometry, while a DFT analysis of complexes 1 and 6 is also provided.