Origins of Initiation Rate Differences in Ruthenium Olefin Metathesis Catalysts Containing Chelating Benzylidenes
Origins of Initiation Rate Differences in Ruthenium Olefin Metathesis Catalysts Containing Chelating Benzylidenes
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DOI：
10.1021/jacs.5b01144
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发表时间：
2015-05-06
影响因子：
15
通讯作者：
Grubbs, Robert H.
中科院分区：
文献类型：
--
作者：
Engle, Keary M.;Lu, Gang;Grubbs, Robert H.
采用反应动力学、x射线晶体学、核磁共振波谱和DFT计算等方法研究了一系列第二代钌烯烃复分解催化剂，以确定螯合邻烷氧基苄基的结构与观察到的引发速率之间的关系。该系列包括先前报道的含有多种苄基修饰的催化剂以及含有环丙氧基、新戊氧基、1-金刚烷氧基和2-金刚烷氧基的四种新催化剂。采用紫外/可见法测定了该系列催化剂的引发率。所有四种新催化剂都被观察到比相应的异丙氧基对照更快的引发，并且2-金刚烷氧基催化剂被发现是迄今为止报道的最快的hoveyda型催化剂之一。对这些催化剂的x射线晶体结构和计算的能量最小化结构的分析表明，Ru-O键长度和Ru-O键强度之间没有相关性。另一方面，发现起始速率与计算的Ru-O键强度密切相关。后一项发现可以通过计算单一热力学参数来合理化和预测催化剂的起爆，而不需要对起爆步骤的机制进行假设。
A series of second-generation ruthenium olefin metathesis catalysts was investigated using a combination of reaction kinetics, X-ray crystallography, NMR spectroscopy, and DFT calculations in order to determine the relationship between the structure of the chelating o-alkoxybenzylidene and the observed initiation rate. Included in this series were previously reported catalysts containing a variety of benzylidene modifications as well as four new catalysts containing cyclopropoxy, neopentyloxy, 1-adamantyloxy, and 2-adamantyloxy groups. The initiation rates of this series of catalysts were determined using a UV/vis assay. All four new catalysts were observed to be faster-initiating than the corresponding isopropoxy control, and the 2-adamantyloxy catalyst was found to be among the fastest-initiating Hoveyda-type catalysts reported to date. Analysis of the X-ray crystal structures and computed energy-minimized structures of these catalysts revealed no correlation between the Ru-O bond length and Ru-O bond strength. On the other hand, the initiation rate was found to correlate strongly with the computed Ru-O bond strength. This latter finding enables both the rationalization and prediction of catalyst initiation through the calculation of a single thermodynamic parameter in which no assumptions about the mechanism of the initiation step are made.