塩化ガリウムで安定したアレン-水銀複合体:H/Dとアレン交換の相対比率
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
まとめ
この研究では,アレンにおける水銀触媒によるH/D交換反応のメカニズムを調査しています. 研究者らは,初期選択性は,電性芳香的置換によって支配され,リガンド交換後の水銀活性化C-H結合にシフトすることを発見しました.
科学分野:
- 有機金属化学 有機金属化学
- 反応メカニズム 反応メカニズム
- カタリシス カタリシス カタリシス
背景:
- Hg ((アレン) 2 ((GaCl4) 2複合体は,H/D交換反応を触媒として作用する.
- 提案されたメカニズムは,協調されたアレーンがC6D6.6をプロトナートする電気的芳香的置換を含む.
研究 の 目的:
- Hg(arene) 2 ((GaCl4) 2を触媒化したH/D交換反応のメカニズムを調査する.
- 具体的には,C6D6とHgによって触媒化されたナフタレンとの反応の運動学を研究することでした (C6H5Me) 2 (GaCl4) 2.
主な方法:
- C6D6とナフタレンの間のH/D交換の運動学的研究.
- ナフタルエンの1位と2位に対する別々の二次レート定数の決定.
- 13C CPMAS NMRおよびUV可視光譜を用いたリガンド交換製品の特性.
主要な成果:
- H/Dの初期為替レートは,ナフタレンの1位と2位 (k1i/k2i比は11から2.5まで) の為替レート常数として異なっていた.
- 速度は時間とともに変化し,最終的には2次流動の定数で新しい安定状態に達した.
- リンガンド交換が起こり,Hg(ナフタレン) 2 ((GaCl4) 2) が形成され,活性化パラメータは解離的メカニズムを示しています.
結論:
- H/D交換メカニズムは,ナフタレンを協調されたC6D6.6で初期に電友性芳香的置換する.
- リガンド交換はメカニズムを変化させ,水銀活性化ナフタレンC-H結合がプロトン化C6D6.6で支配的になる.
- 観測された部位選択性は,電性芳香的置換から水銀媒介C-H活性化への移行と一致しています.
関連する概念動画
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...