High-Valent Uranium Alkyls: Evidence for the Formation of UVI(CH2SiMe3)6
journal contributionposted on 03.08.2011, 00:00 by Skye Fortier, Justin R. Walensky, Guang Wu, Trevor W. Hayton
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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(OtBu)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)(OtBu)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(OtBu)2(CH2SiMe3)4] (4) in moderate yield. We have also attempted the one-electron oxidation of complex 1. Thus, oxidation of 1 with U(OtBu)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.