Lyon Jonathan T, Andrews Lester, Malmqvist Per-Ake, Roos Björn O, Yang Tianxiao, Bursten Bruce E
Department of Chemistry, P.O. Box 400319, Charlottesville, Virginia 22904-4319, USA.
Inorg Chem. 2007 Jun 11;46(12):4917-25. doi: 10.1021/ic062407w. Epub 2007 May 8.
Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3-UH, which undergoes alpha-H transfer to produce uranium methylidene dihydride, CH2=UH2. This rearrangement most likely occurs on an excited-quintet potential-energy surface and is followed by relaxation in the argon matrix. These simple U+CH4 reaction products are identified through isotopic substitution (13CH4, CD4, CH2D2) and density functional theory frequency and structure calculations for the strong U-H stretching modes. Relativistic multiconfiguration (CASSCF/CASPT2) calculations substantiate the agostic distorted C1 ground-state structure for the triplet CH2=UH2 molecule. We find that uranium atoms are less reactive in methane activation than thorium atoms. Our calculations show that the CH2=UH2 complex is distorted more than CH2=ThH2. A favorable interaction between the low energy open-shell U(5f) sigma orbital and the agostic hydrogen contributes to the distortion in the uranium methylidene complexes.
铀原子在紫外线激发下使甲烷活化，形成氢化甲基铀CH₃-UH，其发生α-H转移生成二氢化亚甲基铀CH₂=UH₂。这种重排最有可能发生在激发的五重态势能面上，随后在氩气基质中弛豫。这些简单的U+CH₄反应产物通过同位素取代（¹³CH₄、CD₄、CH₂D₂）以及对强U-H伸缩模式进行密度泛函理论频率和结构计算来确定。相对论多组态（CASSCF/CASPT2）计算证实了三重态CH₂=UH₂分子的C₁基态结构存在弯曲。我们发现铀原子在甲烷活化中的反应性低于钍原子。我们的计算表明，CH₂=UH₂配合物比CH₂=ThH₂的扭曲程度更大。低能量开壳层U(5f) σ轨道与弯曲氢之间的有利相互作用导致了亚甲基铀配合物的扭曲。
