使用 [Tp'Rh ((CNneopentyl)) ] 复合物的化芳化合物的C-H键激活的能量
Meagan E Evans1, Catherine L Burke, Sornanong Yaibuathes
1Department of Chemistry, University of Rochester, Rochester, New York 14627, USA.
Journal of the American Chemical Society
|August 28, 2009
概括
орто效应显著稳定-碳键在化芳化合物中的作用. 这项研究量化了这种效应,揭示了它对C-H键激活和减少性消除障碍的影响.
科学领域:
- 有机金属化学 有机金属化学
- 化学 的化学
- 催化剂是一种催化剂.
背景情况:
- 在合成化学中,C-H键激活是关键的转化.
- 化芳香碳化合物具有独特的电子特性,影响反应性.
- 复合物是C-H激活的有效催化剂.
研究的目的:
- 为了研究替代剂对通过C-H激活形成的-烯键的稳定性的影响.
- 通过实验量化 орто对Rh-C键强度的影响.
- 将实验结果与理论预测进行比较.
主要方法:
- 使用 [Tp'Rh ((CNneopentyl)) ] 复合物激活化芳的C-H键.
- 合成和特征Tp'Rh(CNneopentyl) ((aryl) ((F)) H产品的合成和特征.
- 竞争实验和激活障碍的测量 (DeltaG) 为了确定相对的债券强度.
主要成果:
- 通过C-H激活化烯的产品形成被观察到.
- Rh-C ((aryl) 键的稳定性很大程度上取决于正体素的数量,而不是素总数.
- 与具有两种整形素的复合物相比,具有两种整形素的复合物表现出较高的减少性消除障碍 (~5 kcal mol(-1)) 与具有一个整形素的复合物相比.
- 实验中的Rh-C键强度与理论中的C-H键强度有很好的相关性 (实验斜率为2.14而理论为1.96).
结论:
- 整形效应显著加强了Rh-C(aryl) 键.
- 这项研究首次实验量化了对金属碳键强度的影响,与理论预测保持一致.
- 研究结果为控制含基质的有机金属催化反应活性提供了洞察力.
相关概念视频
Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
Aromatic Hydrocarbon Anions: Structural Overview
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous overlap of p...
Due to the absence of continuous overlap of p...
Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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...


![[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59739.jpg&w=3840&q=50)