烯和I):动态C-H氧化添加和热力学C-Hal氧化添加
Lei Fan1, Sean Parkin, Oleg V Ozerov
1Department of Chemistry, Brandeis University, Waltham, Massachusetts 02454, USA.
Journal of the American Chemical Society
|December 1, 2005
概括
在室温下,A (PNP) Ir片段选择性地增加了C-H键,但在更高的温度下,C-Cl/C-Br键更受欢迎. 这种运动与热力学控制为有机金属化学提供了可调节的反应性.
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:
- 惰性化学键的激活是现代合成化学的基石.
- 复合物以其在C-H激活中的催化活性而闻名.
- 了解氧化添加的选择性对于设计高效的催化系统至关重要.
研究的目的:
- 为了研究一个 (PNP) Ir片段的选择性,在氧化添加的烯和烯.
- 确定控制C-H与C-素键激活的动力学和热力学因素.
- 阐明这些转变的反应路径和能量景观.
主要方法:
- 涉及 (PNP) Ir片段和各种烯和烯基底的实验研究.
- 在不同温度 (室温和100摄氏度以上) 进行反应监测.
- 对产品分布的分析和激活障碍的确定.
主要成果:
- 观察到易于在室温下氧化添加C-H键在体和体中.
- 这种对C-H激活的动力偏好转变为在更高温度 (>100摄氏度) 上对C-Cl和C-Br激活的热力学偏好.
- 一个高激活屏障将C-H和C-的氧化添加产品分开.
- 对于二,正位置换的同位素 (o-ClC6H4联体) 被发现是能量最低的C-H激活产物.
结论:
- (PNP) Ir片段表现出基于温度的可调性选择性,由动力和热力学因素控制.
- 这一发现为控制C-H和C-素键激活中的反应性提供了洞察力.
- 在C-H激活中观察到的区域选择性为有针对性的功能化提供了潜力.
相关概念视频
Introduction to Electrophilic Addition Reactions of Alkenes
The double bond in a simple, unconjugated alkene is a region of high electron density that can act as a weak base or a nucleophile. The filled π orbital (HOMO) of the double bond can interact with the empty LUMO of an electrophile. A bonding interaction occurs when the electrophile attacks between the two carbons; the electrophile then accepts a pair of electrons from the π bond and undergoes addition across the double bond, yielding a single product.
Addition and elimination reactions can be...
Addition and elimination reactions can be...
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.
Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition.
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are formed faster owing to...
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are formed faster owing to...
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.


