Nitro-substituted Hoveyda-Grubbs ruthenium carbenes: Enhancement of catalyst activity through electronic activation
Nitro-substituted Hoveyda-Grubbs ruthenium carbenes: Enhancement of catalyst activity through electronic activation
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DOI：
10.1021/ja048794v
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发表时间：
2004-08-04
影响因子：
15
通讯作者：
Grela, K
中科院分区：
文献类型：
--
作者：
Michrowska, A;Bujok, R;Grela, K
介绍了硝基Hoveyda-GRubbs歧化催化剂的设计、合成、稳定性和催化活性。活性高、稳定性好的间位和对位取代化合物具有很强的实用价值。这些催化剂在非常温和的条件下工作，可以成功地应用于各种类型的复分解反应[闭环复分解反应、交叉复分解反应(CM)和烯炔复分解反应]。尽管NO2基团的存在使催化剂的活性大大高于第二代格拉布斯催化剂和无膦的霍维达卡宾，但反应活性的提高略低于空间活化的霍维达-格拉布斯催化剂。试图将空间和电子两种活化模式结合起来，会严重降低催化剂的稳定性。研究结果表明，不同的Ru催化剂对不同的应用具有较好的效果。虽然无膦卡宾是各种缺电子底物CM的首选催化剂，但它们在形成四取代双键方面表现出较低的反应活性。这表明，在所有可能的应用中，没有一种催化剂比所有其他催化剂表现得更好。
The design, synthesis, stability, and catalytic activity of nitro-substituted Hoveyda-Grubbs metathesis catalysts are described. The highly active and stable meta- and para-substituted complexes are attractive from a practical point of view. These catalysts operate in very mild conditions and can be successfully applied in various types of metathesis [ring-closing metathesis, cross-metathesis (CM), and enyne metathesis]. Although the presence of a NO2 group leads to catalysts that are dramatically more active than both the second-generation Grubbs's catalyst and the phosphine-free Hoveyda's carbene, enhancement of reactivity is somewhat lower than that observed for a sterically activated Hoveyda-Grubbs catalyst. Attempts to combine two modes of activation, steric and electronic, result in severely decreasing a catalyst's stability. The present findings illustrate that different Ru catalysts turned out to be optimal for different applications. Whereas phosphine-free carbenes are catalysts of choice for CM of various electron-deficient substrates, they exhibit lower reactivity in the formation of tetrasubstituted double bonds. This demonstrates that no single catalyst outperforms all others in all possible applications.