Selectivity in the C鈥揌 Activation Reaction of CH3OSO2CH3 with [1,2,4-(Me3C)3C5H2]2CeH or [1,2,4-(Me3C

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• 作者：Evan L. Werkema ; Ludovic Castro ; Laurent Maron ; Odile Eisenstein ; Richard A. Andersen
• 刊名：Organometallics
• 出版年：2012
• 出版时间：February 13, 2012
• 年：2012
• 卷：31
• 期：3
• 页码：870-881
• 全文大小：601K
• 年卷期：v.31,no.3(February 13, 2012)
• ISSN：1520-6041

文摘

The experimental reaction of [1,2,4-(Me₃C)₃C₅H₂]₂CeH, Cp鈥?sub>2CeH, and CH₃OSO₂CH₃ begins by 伪-C鈥揌 activation of the SCH₃ group, forming Cp鈥?sub>2CeCH₂SO₂(OCH₃), which evolves into Cp鈥?sub>2CeOCH₃ with elimination of CH₂ (and presumably SO₂). Prolonged heating of this mixture (days at 60 掳C) forms Cp鈥?sub>2CeOSO₂CH₃ and CH₃OCH₃. The metallacycle [1,2,4-(Me₃C)₃C₅H₂][1,2-(Me₃C)₂-4-(Me₂CCH₂)C₅H₂]Ce, when presented with the choice of C鈥揌 bonds in CH₃S and CH₃O groups, deprotonates both with comparable rates, ultimately forming Cp鈥?sub>2CeOCH₃ and Cp鈥?sub>2CeOSO₂CH₃ at 20 掳C. The experimental studies are illuminated by DFT calculations on the experimental systems, which show that the hydride selects the more acidic CH₃S bond, whereas the metallacycle reacts with C鈥揌 bonds of both the CH₃S and CH₃O groups of CH₃OSO₂CH₃. In the metallacycle reaction, the initially formed regioisomers, Cp鈥?sub>2CeCH₂SO₂(OCH₃) and Cp鈥?sub>2CeCH₂OSO₂CH₃, rearrange to the observed products, Cp鈥?sub>2CeOCH₃ and Cp鈥?sub>2CeOSO₂CH₃, respectively. Furthermore, C鈥揌 activation at the SCH₃ group forms two isomers of Cp鈥?sub>2CeCH₂SO₂(OCH₃) in the reaction of CH₃OSO₂CH₃ with the metallacycle and only one in the reaction with the hydride. The lack of selectivity in the reactions of the metallacycle relative to the hydride is due to the metallacycle鈥檚 greater thermodynamic advantage and lower energy barriers, which are linked to the higher bond energy of Ce鈥揌 relative to Ce鈥揅 in the metallacycle.