B(C6F5) 3-与Al(C6F5) 3-衍生的金属离子对. 结构,热化学和结构动态差异
Nicholas G Stahl1, Michael R Salata, Tobin J Marks
1Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA.
Journal of the American Chemical Society
|August 4, 2005
概括
(Al(C6F5) 3) 合催化剂在4组金属离子对中比 (B(C6F5) 3) 相对应物具有较低的甲基亲和力. 这导致更强的桥接甲基结合,并改变了Al衍生系统的表皮化动力学.
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.
- 主群 化学 化学
背景情况:
- 金属离子对在烯酸聚合催化过程中至关重要.
- 反的选择显著影响着催化剂的活性和稳定性.
- 基甲基化合物,如B(C6F5) 3是常见的激活剂,但与类同类相比,它们的特性尚未完全理解.
研究的目的:
- 量化比较Al (C6F5) 3衍生物与B (C6F5) 3衍生物组4金属离子对的热力学和结构特性.
- 为了研究对抗离子对桥接甲基组的结合强度和随后的离子对表皮化动力学的影响.
- 阐明Al (C6F5) 3和B (C6F5) 3) 之间的甲基亲和关系的差异.
主要方法:
- 使用rac-C2H4(eta5-Ind) 2Zr(CH3) 2和B(C6F5) 3或Al(C6F5) 3.3,合成金属离子对.
- 进行X射线晶体学以确定离子对的结构特征.
- 异二醇溶液热量计用于测量离子对形成热量.
- 可变温度 (VT) 核磁共振 (NMR) 光谱法用于确定离子对表皮化 (共催化剂交换和离子交换) 的动态参数.
主要成果:
- C6F5) 3衍生的离子对与C6F5) 3衍生的离子对相比,表现出较弱的甲基化亲和力,这是较低的离子对形成度所证明的.
- 射线晶体学揭示了Al(C6F5) 3-衍生离子对中的桥接甲基组较少抽象,导致较长的Zr-CH3桥接键长度.
- 动力学研究表明,桥接甲基在Al ((C6F5) 3) 衍生离子对中结合得更强,这与化活性障碍较高相一致.
结论:
- Al ((C6F5) 3) 是一个比B ((C6F5) 3) 弱得多的易斯酸,表现出较低的甲基胺亲和力.
- 和B导离子对之间的结构和热力学差异影响金属催化剂的稳定性和反应性.
- 这些发现为设计针对特定聚合应用的定制催化剂提供了宝贵的见解.
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