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

Abstract

Oxidation of [Li(DME)(3)][U(CH(2)SiMe(3))(5)] with 0.5 equiv of I(2), followed by immediate addition of LiCH(2)SiMe(3), affords the high-valent homoleptic U(V) alkyl complex [Li(THF)(4)][U(CH(2)SiMe(3))(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(CH(2)SiMe(3))(5)] generates the heteroleptic U(IV) complex [Li(DME)(3)][U(O(t)Bu)(2)(CH(2)SiMe(3))(3)] (2) in high yield. Treatment of 2 with AgOTf fails to produce a U(V) derivative, but instead affords the U(IV) complex (Me(3)SiCH(2))Ag(μ-CH(2)SiMe(3))U(CH(2)SiMe(3))(O(t)Bu)(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 Me(3)NO, producing the heteroleptic U(V) complex [Li(DME)(3)][U(O(t)Bu)(2)(CH(2)SiMe(3))(4)] (4) in moderate yield. We have also attempted the one-electron oxidation of complex 1. Thus, oxidation of 1 with U(O(t)Bu)(6) results in formation of a rare U(VI) alkyl complex, U(CH(2)SiMe(3))(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.

A Rare Uranyl(VI)–Alkyl Ate Complex [Li(DME)1.5]2[UO2(CH2SiMe3)4] and Its Comparison with a Homoleptic Uranium(VI)–Hexaalkyl

“…[19] This result contrasts greatly with our original assignment, which placed the resonance of the methylene moiety at 34.0 ppm in [D 8 ]THF at À40 8C. [5] However, it should be noted that the direct-detection 13 C{ 1 H} NMR experiment was not performed with a large enough sweep width to observe a signal beyond 300 ppm.…”

“…[23,25,26] Our success in isolating and characterizing complex 1 prompted us to revisit the synthesis of [U(CH 2 SiMe 3 ) 6 ] (2), which we initially reported in 2011. [5] Based on the recent theoretical study by Hrobµrik et al, the 13 C NMR chemical shift for the methylene carbon atoms of 2 is predicted to occur at an unprecedentedly high frequency when compared to other diamagnetic compounds. [19] This result contrasts greatly with our original assignment, which placed the resonance of the methylene moiety at 34.0 ppm in [D 8 ]THF at À40 8C.…”

“…In contrast, the organometallic chemistry of the 5 + and 6 + states has lagged behind considerably. [4][5][6] This is especially true for the uranyl ion, the most studied fragment in uranium chemistry. [7] Despite the fact that the preparation of organometallic uranyl complexes has been attempted for over 150 years, [8] the first uranyl-hydrocarbyl complex was only reported in 2002.…”

“…The strategy of "ate" complex formation has also allowed us to stabilize several homoleptic uranium-alkyl complexes in the 4 + , 5 + , and 6 + oxidation states, as well as several homoleptic thorium-alkyl complexes. [5,17,18] Their synthesis and characterization, in conjunction with quantum-chemical calculations, has enabled the study of the contribution of the 6d and 5f valence orbitals in actinide À carbon bonds. These results inspired us to explore the synthesis of a uranyl-alkyl "ate" complex to gain further insight into the U À C bonding interactions.…”

Synthesis, structure and bonding of hexaphenyl thorium(iv): observation of a non-octahedral structure

“…In this regard, we, and others, have made several attempts to isolate homoleptic alkyl complexes of thorium 10,11 and uranium. [12][13][14][15] Despite considerable synthetic efforts, previous attempts have resulted in the isolation and structural characterization of only three homoleptic Th alkyl complexes, namely, the 5-coordinate complex [Li (THF) 6 ]. 12,13 The latter was oxidized in situ to U(CH 2 SiMe 3 ) 6 , which was characterized using 13 C and 1 H NMR spectroscopies, accompanied by relativistic DFT calculations of NMR chemical shifts.…”