用金属催化剂在烯聚合过程中的链式表皮化:使用双重标记的烯进行机械研究
Jeffrey C Yoder1, John E Bercaw
1Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, CA 91125, USA.
Journal of the American Chemical Society
|March 14, 2002
概括
在烯聚合过程中使用同位素标记的烯研究了连锁表皮化. 这些发现表明一种涉及β-D消除和插入的机制,不包括基/二复合物.
科学领域:
- 聚合物化学 聚合物化学
- 有机金属化学 有机金属化学
- 频谱学是一种光谱学.
背景情况:
- 使用金属催化剂的烯聚合对于生产多聚烯至关重要.
- 了解链 épimerization 机制是控制聚合物立体化学的关键.
- 像rac-{EBTHI) ZrCl{2}和rac-{EBI) ZrCl{2}等同特异性催化剂通常产生高度立体规律的聚烯.
研究的目的:
- 阐明在烯聚合过程中链性表皮化过程的详细机制.
- 调查特定中间体在立体化学错误中的作用.
- 使用同位素标记来区分拟议的表皮化途径.
主要方法:
- 合成同位素标记的烯 (CH(2)=CD(13) CH(3)).
- 使用甲基氨酸激活的rac-(EBTHI) ZrCl(2) 和rac-(EBI) ZrCl(2) 催化剂进行烯聚合.
- 使用碳-13核磁共振 ((13) C NMR) 光谱分析聚合物微观结构.
主要成果:
- 归因于链式表皮化,在较低烯度和中等温度下观察到的立体错误.
- (13)C 核磁共振检测显示,在各种五度和七度序列中,特定的 (13)C 标记的甲组和同位素单位 ([CD(13) CH(3) ],[CH(13) CH(3)) 存在.
- 观察到的错误与涉及β-D消除,烯酸旋转,enantiofacial互转换和插入到第三级基中间体的机制一致,随后是相反的步骤.
结论:
- 这项研究提供了强有力的证据,证明了这些金属催化聚合物的特定链式表皮化机制.
- 在特定的五度中缺少某些标记单位 ([CH(2) CH(13) CH(2) D-) 排除了作为中介物种的基/二基复合物.
- 这种详细的机制理解有助于设计催化剂,以更好地控制聚烯立体规律性.
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