DFT Studies on the Methane Elimination Reaction of a Trinuclear Rare-Earth Polymethyl Complex: 蟽-Bond Metathesis Assisted by Cooperation of Multimetal Sites

详细信息    查看全文

• 作者：Gen Luo ; Yi Luo ; Wenxiong Zhang ; Jingping Qu ; Zhaomin Hou
• 刊名：Organometallics
• 出版年：2014
• 出版时间：March 10, 2014
• 年：2014
• 卷：33
• 期：5
• 页码：1126-1134
• 全文大小：534K
• 年卷期：v.33,no.5(March 10, 2014)
• ISSN：1520-6041

文摘

DFT studies have been performed for the process of methane elimination via an intramolecular C鈥揌 bond activation of the polymethyl trinuclear rare-earth-metal complex [(畏⁵-C₅Me₄SiMe₃)Tm(渭₂-CH₃)₂]₃. It has been found that intermetallic cooperation plays an important role in achieving such an intramolecular C鈥揌 bond activation process, and the cooperation of trimetallic centers makes the C鈥揌 bond activation kinetically easier in comparison with that of bimetallic centers. The methane elimination reaction occurs through rearrangement of Tm鈥揅H₃ connections and subsequent C鈥揌 bond activation. The C鈥揌 bond activation is the rate-determining step of the whole process, and the corresponding transition state is characterized by a 蟽-bond metathesis assisted by cooperation of multimetal sites. Such a C鈥揌 bond activation step was accomplished by a change in the coordination manner (from 渭₂ to 渭₃ fashion) of a methyl group and a subsequent hydrogen transfer, and the two events are asynchronous concerted processes. The computational results also suggest that the reactivity of the C鈥揌 bond of the metal-connected CH₃ group follows the order 渭₃-C(H₂)鈥揌 > 渭₂-C(H₂)鈥揌 > 渭₁-C(H₂)鈥揌. This is unlike the case of a metal鈥揅H₃ bond, where the terminal methyl (monometal-connected 渭₁-CH₃) is generally more reactive than multimetal-connected methyls. In addition, the effect of 4f electrons of such trinuclear organolanthanide compounds on the geometry and energy profile studied here is also discussed.