在Pd-Pd-Pd部分上对联四烯配体的光诱导面部反转
Tetsuro Murahashi1, Yutaka Higuchi, Tetsuya Katoh
1Department of Applied Chemistry and Frontier Research Center, Faculty of Engineering, Osaka University, Suita, Osaka, 565-0871, Japan. tetsu@chem.eng-u.ac.jp
Journal of the American Chemical Society
|November 28, 2002
概括
观察到线性三三复合物的光诱导异构. 可见光引起了四烯联体的分层 (rac) 和阴影 (meso) 排列之间的切换,由X射线晶体学证实.
科学领域:
- 有机金属化学 有机金属化学
- 摄影化学的使用.
- 晶体学 晶体学是指结晶学.
背景情况:
- 线性三三复合体具有独特的结构性质.
- 这些复合体中的四烯联体可以经历形状变化.
研究的目的:
- 为了研究线性三明治三复合物的光诱导异构化.
- 为了阐明辐射时涉及四烯联体的结构变化.
主要方法:
- 用可见光 (>510 nm) 对三复合物的辐射.
- 使用X射线晶体分析确定异构体的结构.
主要成果:
- 从rac (分阶三明治) 到 meso (阴影三明治) 形式的光诱导异构化得到了实现.
- 成功确定了rac和meso同体的结构.
结论:
- 可见光在线性三三复合体中触发面反转异构.
- X射线晶体学为观察到的rac-meso转换提供了明确的结构证据.
相关概念视频
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.
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
Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.

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