High-Valent Uranium Alkyls: Evidence for the Formation of UVI(CH2SiMe3)6

Oxidation of [Li(DME)(3)][U(CH2SiMe3)(5)] with 0.5 equiv of I-2, 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((OBu)-Bu-t)(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(mu-CH2SiMe3)U(CH2SiMe3)((OBu)-Bu-t)(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((OBu)-Bu-t)(2)(CH2SiMe3)(4)] (4) in moderate yield. We have also attempted the one-electron oxidation of complex 1. Thus, oxidation of 1 with U((OBu)-Bu-t)(6) results in formation of a rare U(VI) alkyl complex, U(CH2SiMe3)(6) (6), which is only stable below -25 degrees 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.