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首页> 外文期刊>Chemistry: A European journal >Origins of Large Rate Enhancements in the Nazarov Cyclization Catalyzed by Supramolecular Encapsulation
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Origins of Large Rate Enhancements in the Nazarov Cyclization Catalyzed by Supramolecular Encapsulation

机译：超分子包封催化纳扎罗夫环化反应大幅度提高的起源

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摘要

The self-assembled supramolecular host [Ga_4L_6]~(12-) (1; L=N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) catalyzes the Nazarov cyclization of 1,3-pentadienols with extremely high levels of efficiency. The catalyzed reaction proceeds at a rate over a million times faster than that of the background reaction, an increase comparable to those observed in some enzymatic systems. A detailed study was conducted to elucidate the reaction mechanism of both the catalyzed and uncatalyzed Nazarov cyclization of pentadienols. Kinetic analysis and ~(18)O-exchange experiments implicate a mechanism, in which encapsulation, protonation, and water loss from substrate are reversible, followed by irreversible electrocyclization. Although electrocyclization is rate determining in the uncatalyzed reaction, the barrier for water loss and for electrocyclization are nearly equal in the assembly-catalyzed reaction. Analysis of the energetics of the catalyzed and uncatalyzed reaction revealed that transition- state stabilization contributes significantly to the dramatically enhanced rate of the catalyzed reaction.
机译：自组装的超分子主体[Ga_4L_6]〜（12-）（1; L = N，N-双（2,3-二羟基苯甲酰基）-1,5-二氨基萘）催化Nazarov对1,3-戊二烯醇的环化反应高效率。催化反应的进行速度比背景反应快一百万倍，与某些酶体系中观察到的增加相当。进行了详细的研究，以阐明戊二烯醇的催化和未催化纳扎罗夫环化反应的机理。动力学分析和〜（18）O交换实验暗示了一种机理，其中包封，质子化和从底物流失是可逆的，然后进行不可逆的电环化。尽管在未催化反应中电环化是决定速率的，但在组装催化反应中水损失和电环化的障碍几乎相等。对催化和未催化反应的能量学分析表明，过渡态的稳定化极大地促进了催化反应的速率。

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