结合基复合物的协调模式控制反应性:在低温下拦截终端基-Mo(III) 基
Meaghan E Germain1, Manuel Temprado, Annie Castonguay
1Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massachusetts 02155, USA.
Journal of the American Chemical Society
|November 19, 2009
概括
这项研究研究了金属-化复合物的反应性,揭示了连接体结合触觉性如何影响反应途径和速率. 了解这些动态对于设计新的催化过程至关重要.
科学领域:
- 有机金属化学 有机金属化学
- 协调化学 协调化学
- 反应动力学反应动力学
背景情况:
- 已知Mo(N[(t) Bu]Ar)(3) (1) 类型的复合物可以结合.
- 亚烯配体的触觉性 (eta(1) 与eta(2)) 可以显著改变它们的反应性.
- 了解控制这些相互作用的热力学和动力学参数是控制化学转换的关键.
研究的目的:
- 为了确定以Mo(N[(t) Bu]Ar) ((3) 形成酸复合物的热力学数据.
- 为了研究烯结合,异构和随后的氧化添加反应的动力学和机制.
- 阐明连接体触觉性在决定金属-化复合物的反应性方面的作用.
主要方法:
- 变量温度平衡研究以获得热力学数据 (DeltaH,DeltaS).
- 溶液热量计用于形成测量的度.
- 停止流动的动力学研究,以确定速度和激活参数.
- 密度函数理论 (DFT) 计算用于研究中间结构.
主要成果:
- 对于不同烯 (AdCN,PhCN,MesCN) 的烯复合物形成的热力学数据被量化.
- 发现eta(2) -NCNMe(2) 复合物的形成比eta(1) 结合更为外热.
- 动力学研究揭示了Me(2) NCN的两步结合过程,涉及eta(1) 和eta(2) 的中间体.
- 氧化添加PhSSPh到eta(1) 结合的烯酸是快速的,而添加到eta(2) 结合的烯酸是显著的慢.
- DFT的计算证实了酸中碳原子的部分基质特性.
结论:
- 已经建立了对联体结合,异构化和氧化添加的综合反应概况.
- 连接体的触觉性对氧化添加反应的速率和途径产生重要影响.
- 这项研究提供了对金属-烯复合物的反应性的见解,对催化和合成化学有意义.
相关概念视频
Radical Reactivity: Intramolecular vs Intermolecular
Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
Radical Reactivity: Concentration Effects
In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...
Radical Reactivity: Overview
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Radical Reactivity: Nucleophilic Radicals
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
Preparation of Nitriles
One of the common methods to prepare nitriles is the dehydration of amides. This method requires strong dehydrating agents like phosphorous pentoxide or boiling acetic anhydride for converting amides to nitriles. Another reagent namely, thionyl chloride also accomplishes the dehydration of amides, where amide acts as a nucleophile. The first step of the mechanism involves the nucleophilic attack by the amide on the thionyl chloride to form an intermediate. In the next step, the electron pairs...


