Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.
Acc Chem Res. 2015 Feb 17;48(2):306-16. doi: 10.1021/ar500375j. Epub 2014 Dec 23.
Frustrated Lewis pair (FLP) chemistry has emerged in the past decade as a strategy that enables main-group compounds to activate small molecules. This concept is based on the notion that combinations of Lewis acids and bases that are sterically prevented from forming classical Lewis acid-base adducts have Lewis acidity and basicity available for interaction with a third molecule. This concept has been applied to stoichiometric reactivity and then extended to catalysis. This Account describes three examples of such developments: hydrogenation, hydroamination, and CO2 reduction. The most dramatic finding from FLP chemistry was the discovery that FLPs can activate H2, thus countering the long-existing dogma that metals are required for such activation. This finding of stoichiometric reactivity was subsequently evolved to employ simple main-group species as catalysts in hydrogenations. While the initial studies focused on imines, subsequent studies uncovered FLP catalysts for a variety of organic substrates, including enamines, silyl enol ethers, olefins, and alkynes. Moreover, FLP reductions of aromatic anilines and N-heterocycles have been developed, while very recent extensions have uncovered the utility of FLP catalysts for ketone reductions. FLPs have also been shown to undergo stoichiometric reactivity with terminal alkynes. Typically, either deprotonation or FLP addition reaction products are observed, depending largely on the basicity of the Lewis base. While a variety of acid/base combinations have been exploited to afford a variety of zwitterionic products, this reactivity can also be extended to catalysis. When secondary aryl amines are employed, hydroamination of alkynes can be performed catalytically, providing a facile, metal-free route to enamines. In a similar fashion, initial studies of FLPs with CO2 demonstrated their ability to capture this greenhouse gas. Again, modification of the constituents of the FLP led to the discovery of reaction systems that demonstrated stoichiometric reduction of CO2 to either methanol or CO. Further modification led to the development of catalytic systems for the reduction of CO2 by hydrosilylation and hydroboration or deoxygenation. As each of these areas of FLP chemistry has advanced from the observation of unusual stoichiometric reactions to catalytic processes, it is clear that the concept of FLPs provides a new strategy for the design and application of main-group chemistry and the development of new metal-free catalytic processes.
frustrated Lewis pair (FLP) 化学在过去十年中作为一种使主族化合物能够激活小分子的策略出现。这个概念基于这样的观点，即空间位阻阻止形成经典路易斯酸碱加合物的路易斯酸和碱组合具有可供与第三种分子相互作用的路易斯酸度和碱度。该概念已应用于计量反应，然后扩展到催化领域。本综述描述了此类发展的三个示例：氢化、氢胺化和 CO2 还原。FLP 化学最引人注目的发现是发现 FLP 可以激活 H2，从而反驳了长期存在的金属是此类激活所必需的教条。这种计量反应性的发现随后被演变为使用简单的主族物种作为氢化反应的催化剂。虽然最初的研究集中在亚胺上，但随后的研究发现了各种有机底物的 FLP 催化剂，包括烯胺、硅基烯醇醚、烯烃和炔烃。此外，还开发了芳香族苯胺和 N-杂环的 FLP 还原，而最近的扩展揭示了 FLP 催化剂在酮还原中的应用。FLP 也已被证明与末端炔烃发生计量反应。通常，观察到去质子化或 FLP 加成反应产物，这主要取决于路易斯碱的碱性。虽然已经利用了各种酸碱组合来获得各种两性离子产物，但这种反应性也可以扩展到催化领域。当使用仲芳基胺时，可以催化进行炔烃的氢胺化，提供一种简便的、无金属的制备烯胺的方法。以类似的方式，对 CO2 的初始 FLP 研究表明它们能够捕获这种温室气体。同样，对 FLP 组成部分的修饰导致发现了将 CO2 定量还原为甲醇或 CO 的反应体系。进一步的修饰导致了通过硅氢化和硼氢化或脱氧还原来还原 CO2 的催化体系的开发。随着 FLP 化学的每个领域从观察到不寻常的计量反应到催化过程的发展，很明显，FLP 的概念为设计和应用主族化学以及开发新的无金属催化过程提供了一种新策略。
