由化稳定的-复合物:H/D和交换的相对速率
Catherine S Branch1, Andrew R Barron
1Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77005, USA.
Journal of the American Chemical Society
|November 21, 2002
概括
这项研究研究了催化H/D交换反应在中的机制. 研究人员发现,初始选择性是由电友芳香替代控制的,在交换后转向活性化C-H键.
科学领域:
- 有机金属化学 有机金属化学
- 反应机制 反应机制
- 催化剂是一种催化剂.
背景情况:
- 复合物Hg (arene) 2 (GaCl4) 2催化了H/D交换反应.
- 一个拟议的机制涉及电友芳香替代,其中协调的基质突变为C6D6.
研究的目的:
- 为了研究催化H/D交换反应的Hg (arene) 2 (GaCl4) 2的机制.
- 具体来说,是为了研究C6D6和由Hg(C6H5Me) 2(GaCl4) 2. 2催化的纳夫他林之间的反应的动力学.
主要方法:
- 关于C6D6和甲之间H/D交换的动力学研究.
- 确定单独的二次速率常数,用于纳二烯的1和2位.
- 使用13C CPMAS NMR和UV可见光谱学对联体交换产品进行表征.
主要成果:
- 最初的H/D汇率显示了甲烯1和2位的不同汇率常数 (k1i/k2i比率从11到2.5).
- 速度随着时间的推移而变化,最终达到一个新的稳定状态,具有恒定的二次动力学.
- 发生了连接物交换,形成了Hg(纳二烯) 2 ((GaCl4) 2 ,激活参数表明了解离机制.
结论:
- 该H/D交换机制涉及初始电友芳香替代纳夫他林由协调C6D6.6的替代.
- 交换改变了该机制,激活的甲C-H键在质子化C6D6.6中占主导地位.
- 观察到的位点选择性与从电友芳香替代过渡到介导的C-H激活相一致.
相关概念视频
03:45Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
01:07Ladder Diagrams: Complexation Equilibria
Ladder diagrams are useful for evaluating equilibria involving metal-ligand complexes. The vertical scale of the ladder diagram represents the concentration of unreacted or free ligand, pL. The horizontal lines on the scale depict the log of stepwise formation constants for metal-ligand complexes and indicate the dominant species in all the regions.
The formation constant, K1, for the formation of Cd(NH3)2+ complex from cadmium and ammonia is 3.55 × 102. Log K1 (i.e. pNH3) is 2.55, and...
The formation constant, K1, for the formation of Cd(NH3)2+ complex from cadmium and ammonia is 3.55 × 102. Log K1 (i.e. pNH3) is 2.55, and...
01:23Complexation Equilibria: Overview
Complexation reactions take place when dative or coordinate covalent bonds form between metal ions and ligands. The compounds formed in these reactions are called coordination compounds. The number of bonds formed between the metal ion and the ligands is called its coordination number. Generally, most metal ions in an aqueous solution are solvated by water molecules and thus exist as aqua complexes.
The equilibrium constant of the complexation reaction is represented as the formation constant...
The equilibrium constant of the complexation reaction is represented as the formation constant...
01:26EDTA: 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...
01:09Complexation 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...
00:43Complexometric 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...