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相关概念视频

Metal-Ligand Bonds02:51

Metal-Ligand Bonds

The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
Complexation Equilibria: The Chelate Effect01:19

Complexation Equilibria: The Chelate Effect

In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...
EDTA: Chemistry and Properties01:22

EDTA: Chemistry and Properties

Polydentate ligands are most widely used in complexometric titrations because they form more stable complexes with the metal ions than mono- or bidentate ligands due to the chelate effect. Examples of polydentate ligands are ethylenediaminetetraacetic acid (EDTA), crown ethers, and cryptands. The most important feature of optimal polydentate ligands is the ability to form 1:1 complexes in a single-step process. Amino carboxylic acid derivatives are frequently used as complexing agents. EDTA is...
EDTA: Auxiliary Complexing Reagents01:26

EDTA: Auxiliary Complexing Reagents

EDTA titrations are usually carried out in highly basic conditions, where the fully deprotonated form of EDTA, Y4−, actively complexes with the free metal ions in the solution. Several metal ions precipitate as hydrous oxide (hydroxides, oxides, or oxyhydroxides) under these conditions, lowering the concentration of free metal ions in the solution. For this reason, auxiliary complexing agents or ligands such as ammonia, tartrate, citrate, or triethanolamine are used in EDTA titrations to...
Complexation Equilibria: Factors Influencing Stability of Complexes01:09

Complexation Equilibria: Factors Influencing Stability of Complexes

In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
Complexometric Titration: Ligands00:43

Complexometric Titration: Ligands

Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...

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Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions
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在Pd(0) 和Pd(II) 上,对硬质要求高的混合型伊米达酸连接体的协调变化.

Douglas B Grotjahn1, Yi Gong, Lev Zakharov

  • 1Department of Chemistry and Biochemistry, San Diego State University, California 92182-1030, USA. grotjahn@chemistry.sdsu.edu

Journal of the American Chemical Society
|January 13, 2006
PubMed
概括

研究人员探索了低坐标有机金属复合体的新杂交配体,发现重的氨酸替代剂有利于化. 这项工作提供了通过连接体设计在催化中控制反应速率和产品的见解.

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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.
  • 连接体设计 连接体设计

背景情况:

  • 低坐标的有机金属复合物对于催化是至关重要的.
  • 混合配体,使得hemilability和二次相互作用正在获得关注.
  • 了解控制这些联结体特性的因素是必不可少的.

研究的目的:

  • 为了合成和研究新的伊米达-2-啡联体.
  • 为了探索由此产生的复合物的协调行为.
  • 了解连接体结构如何影响氧化加法中的反应性.

主要方法:

  • 合成了三种新型的imidazol-2-ylphosphine连接体,其硬质体质量不同.
  • 两个坐标的L2Pd(0) 复合体的形成和表征.
  • 使用X射线衍射和NMR光谱学对氧化添加反应的研究.

主要成果:

  • 合成的L2Pd(0) 复合体存在于两个坐标,12电子的物种.
  • 在氧化添加剂中的反应结果可以通过配体替代剂和基质进行调整.
  • 大量的氨酸组 (三-丁) 促进eta(2) -P,N化,形成单体复合物.
  • 在一个离子复合体中观察到血溶性,其带交换取决于温度.
  • 在imidazole周围的固体阻碍会影响 Pd-N 键的长度.

结论:

  • 结体质量是控制复合物的协调和反应性的关键因素.
  • 伊米达-2-ylphosphine连接物提供可调整的溶化能力和二次相互作用能力.
  • 这项研究为设计先进的有机金属催化剂提供了基础.