竞争性ArC-H和ArC-X (X = Cl, Br) 在基中心的基中激活
Kuangbiao Ma1, Warren E Piers, Masood Parvez
1Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada T2N 1N4.
Journal of the American Chemical Society
|March 9, 2006
概括
甲基酸盐与反应,形成化. 这些化物激活中C-X或C-H键,反应途径受压力影响,揭示了三种不同的键激活机制.
科学领域:
- 有机金属化学 有机金属化学
- 催化剂是一种催化剂.
- 反应机制 反应机制
背景情况:
- 复合物与胺联体因其反应性而闻名.
- 酸盐化物是催化循环中的多功能中间体.
- 二激活是有机合成中的一个关键转化.
研究的目的:
- 为了研究甲基离子与二的反应性.
- 为了探索由此产生的化与化的键激活通路.
- 阐明直接C-X激活,正形C-H激活和间接C-X激活的机制.
主要方法:
- [Cp*((tBu3P=N) TiCH3]+与H2的反应形成了阴离子化物.
- 在不同的H2压力下,化与甲或甲的随后反应.
- 反应产品的分离和表征.
- 机理学研究包括热稳定性测试和反应路径分析.
主要成果:
- 化的形成 [Cp*((tBu3P=N) TiH(THF) n]+ (1).
- 在~4 atm H2 时,直接的 C-X 激活会产生 [Cp*(((tBu3P=N) TiX]+ (2X) 的光.
- 在较低的H2压力 (>1 atm) 时,正正C-H激活产生β-烯酸[Cp*((tBu3P=N) Ti(2-X-C6H4) ]+ (3X).
- 化合物3X在加热时经历β-素消除以形成2X和添加物 (4X).
结论:
- 化系统表现出三种不同的键激活模式:直接的C-X,正形C-H和间接的C-X通过β-素消除.
- 反应途径可以通过调整二压力来控制.
- 机理学研究支持C-X裂变的基因通路,用于C-H激活的西格玛键转化和β-素消除.
相关概念视频
Electrophiles
This lesson explains the definition, classification, and characteristic features of an electrophile that are key features of nucleophilic substitution reactions. An analysis of their charge and orbital picture helps understand their reactivity for seeking electrons. Electrophiles can be classified into positive and neutral species. Other classes include free radicals and polar functional groups.
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...
Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.
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...
Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene
Chlorination and bromination are important classes of electrophilic aromatic substitutions, where benzene reacts with chlorine or bromine in the presence of a Lewis acid catalyst to give halogenated substitution products. A Lewis acid such as aluminium chloride or ferric chloride catalyzes the chlorination, and ferric bromide catalyzes the bromination reactions. During the bromination of alkenes, bromine polarizes and becomes electrophilic. However, in the bromination of benzene, the bromine...
Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.


