通过阴离子 () 复合物的C[键]H激活:联体电子和固体效应
H Annita Zhong1, Jay A Labinger, John E Bercaw
1Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, USA.
Journal of the American Chemical Society
|February 14, 2002
概括
() 复合物与二 () 胺连接物激活中的C-H键,产生基. 在这种催化过程中,立体和电子因素会影响CH激活或协调是否具有决定性作用.
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.
- 在C-H激活激活.
背景情况:
- 双 () 二胺结合甲基 (II) 复合物是催化C-H激活反应中的关键中间体.
- 了解调节芳香系统中C-H键激活的因素对于开发新的催化转换至关重要.
研究的目的:
- 为了研究由阴离子Pt(II) 复合体对的C-H激活的机制.
- 为了确定连接体电子和硬质性质对反应路径和速率决定步骤的影响.
主要方法:
- 合成各种双烯二胺结合甲基Pt2复合物.
- 这些复合物的与三乙醇中的和替代的反应.
- 反应产物的分析和动力学研究,包括同位素效应.
主要成果:
- 阴阳性Pt(II) 复合物与相反应,通过Pt(IV) 中间体形成类Pt(II) 阴阳.
- 芳香C-H激活优于基C-H激活,尽管固醇可以改变这一点.
- 确定速率的步骤从C-H激活切换到协调,随着连接体的硬质体积的增加.
- 连接体的电子特性主要影响基态稳定性和基质访问的便利性,而不是C-H激活步骤本身.
结论:
- 替代的机制涉及一种溶剂辅助的关联途径.
- 双烯二胺联体的固体和电子性质显著调节了由Pt2复合体激活C-H的反应性和机制.
- 观察到的反应速率趋势主要归因于影响基质协调的基态效应,而不是C-H激活步骤.
相关概念视频
02:48Ionic Bonding and Electron Transfer
Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence shell, and an anion (a negative ion) forms when a neutral atom gains one or more electrons in its valence shell. Compounds composed of ions are called ionic compounds (or salts), and their constituent ions are held together by ionic bonds: electrostatic forces of attraction between oppositely charged cations and anions.
02:46Covalent Bonding and Lewis Structures
Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual attraction of atoms for a “shared” pair of electrons.
01:17Thermal 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.
01:26Photochemical 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
00:54Radical Formation: Homolysis
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
01:04¹³C NMR: ¹H–¹³C Decoupling
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...