在金属离子对中的溶液结构和聚合的NOE和PGSENMR光谱研究
Cristiano Zuccaccia1, Nicholas G Stahl, Alceo Macchioni
1Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
Journal of the American Chemical Society
|February 5, 2004
概括
这项研究揭示了金属催化剂结构如何在溶液中发生变化,从而区分内部和外部球体离子对. 外球离子对在较高度下倾向于聚合,影响催化活性.
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.
- 聚合方式的聚合.
背景情况:
- 金属复合物是烯聚合物的关键同质催化剂.
- 了解它们的溶液状态结构是优化催化性能的关键.
- 以前的研究往往侧重于固态结构,解决方案数据有限.
研究的目的:
- 阐明各种金属离子对的溶液结构.
- 为了研究反离子协调 (内部与外部球) 对离子对结构的影响.
- 为了确定这些催化物种的度依赖的聚合行为.
主要方法:
- 解决方案结构的研究使用了核过量效应光谱 (NOESY) 和异核NOE光谱 (HOESY) NMR.
- 使用脉冲梯度旋转回声 (PGSE) NMR进行扩散测量,以探测聚合.
- 实验是在和等低允许度溶剂中进行的.
主要成果:
- 内球离子对表现出与其固态形式相似的结构,具有特定的离子向量方向.
- 外球离子对显示离子离子位于离子的活性位点更远的地方.
- 外球离子对,特别是复杂8的离子对,表现出度依赖的聚合,形成0.5mM以上的更高阶结构.
结论:
- 反离子的协调模式 (内部与外部球) 在很大程度上决定了内部离子溶液的结构.
- 外球离子对在相关的催化度下容易聚合,与内球对应物不同.
- 外球离子对的聚合可以导致结构特异性的损失,并可能影响催化结果.
相关概念视频
02:51Metal-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...
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...
01:06Nuclear Overhauser Enhancement (NOE)
Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...