同位素效应和选择性的性质在催化循环化中
Daniel T Nowlan1, Timothy M Gregg, Huw M L Davies
1Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, USA.
Journal of the American Chemical Society
|December 18, 2003
概括
迪罗四碳酸盐催化剂通过罗碳化物中间体促进烯循环化. 动态同位素效应和DFT计算揭示了异步过渡状态,并证实了这种关键有机转换的碳化物机制.
科学领域:
- 有机金属化学 有机金属化学
- 不对称的催化剂.
- 反应机制研究 反应机制研究
背景情况:
- 迪罗四碳酸盐复合物是广泛用于循环化反应的催化剂.
- 了解精确的机制,包括过渡状态几何和中间体,对于催化剂设计和优化至关重要.
- 动态同位素效应和计算方法是阐明反应途径的强大工具.
研究的目的:
- 通过使用各种二乙酸盐,研究四碳酸催化基的基环化机制.
- 确定过渡状态的性质 (例如同步与异步) 并确定关键中间体.
- 为了验证密度函数理论 (DFT) 的计算与实验动态同位素效应数据相对应.
主要方法:
- 测量碳-13动态同位素效应 (KIEs) 在不同的烯位置.
- 密度函数理论 (DFT) 的计算,特别是使用B3LYP函数.
- 实验KIE与理论预测值的比较,以验证拟议的机制.
主要成果:
- 显著的 (13) C KIE 表示高度异步的环化过渡状态.
- 实验和计算数据强烈支持一种涉及碳化物中间体的机制.
- DFT计算准确地预测了反应障碍,立体选择性和反应性趋势,验证了理论模型.
结论:
- 循环化机制通过碳化物形成,然后通过异步协同过渡状态进行.
- 状二催化剂保持类似的过渡状态几何,影响立体选择性.
- 建议在Rh{2}{S}-DOSP}{4}-催化环化物中建立一个新的酶选择性模型.
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