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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
在基因 - 碳交叉点的化学:一个金属环丁 - 3-乙烯碳平衡
Joseph M O'Connor1, Kim K Baldridge, Carmen L Vélez
1Department of Chemistry, University of California, San Diego, La Jolla, California 92093, USA. jmoconnor@ucsd.edu
Journal of the American Chemical Society
|June 1, 2013
概括
研究人员合成了一个硬质阻碍的金属基丁复合物,观察了第一个金属基丁-η(3) - 乙烯碳化合物平衡. 这一发现为有机金属化学和反应机制开辟了新的途径.
科学领域:
- 有机金属化学 有机金属化学
- 合成化学 合成化学
- 反应机制 反应机制
背景情况:
- 金属环丁复合物是各种催化循环中的关键中间体.
- 了解它们的反应性对于设计新的合成方法至关重要.
- 固态拥堵通常会影响金属复合物的稳定性和反应路径.
研究的目的:
- 为了合成一种硬质阻碍的金属循环布丁复合物.
- 为了研究金属环丁-η(3) - 乙烯碳化合物平衡的潜力.
- 描述由此产生的乙烯基碳基物种并探索其反应性.
主要方法:
- 合成一个固态拥挤的金属环丁复合物.
- 光谱分析 (NMR,IR等) 进行. 用于结构阐明.
- 高分辨率质谱仪 (HRMS) 用于精确的质量测定.
- 一开始的计算研究,以了解电子结构和结合.
- 与电友 (乙二酸乙烯) 和金属复合物 ((C5H5) Co(PPh3) 2) 的捕获反应.
主要成果:
- 实现了第一个金属环丁-η(3) - 乙烯碳平衡的观测.
- 成功阐明了 η(3) - 乙烯基碳化合物的结构.
- 乙烯基碳化合物复合物是反应性的,可以被捕获以形成二烯和二化合物复合物.
结论:
- 固态拥堵可以促进新的反应途径,包括碳平衡.
- η(3) - 乙烯基碳烯中间体是一种具有明显反应性的可活性物种.
- 这项工作提供了对金属环丁复合物的动态行为的洞察.
相关概念视频
Preparation of Alkynes: Alkylation Reaction
Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement
The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a concerted pericyclic reaction proceeding via a chair-like transition state.
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
