Kolychev Eugene L, Theuergarten Eileen, Tamm Matthias
Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.
Top Curr Chem. 2013;334:121-55. doi: 10.1007/128_2012_379.
The use of N-heterocyclic carbenes (NHCs) for the design and construction of frustrated Lewis pairs (FLPs) is outlined in this review. Stable carbene-borane adducts are briefly discussed, followed by a detailed survey of the reactivity of NHCs, in particular Arduengo-type imidazolin-2-ylidenes, towards B(C6F5)3. Structural and electronic NHC modification by variation of substituents and ring-size affords either stable normal adducts or FLPs, which undergo manifold deactivation reactions in the absence of substrates, e.g., by abnormal adduct formation, self-dehydrogenation, and other types of C-H and C-F bond activation. The degree of frustration is correlated with the calculated energies for the formation of the normal adducts NHC·B(C6F5)3, allowing one to predict and rationalize their reactivity towards small molecules such as dihydrogen, ethers, alkynes, main group elements, carbon dioxide, and nitrous oxide. Other carbene-based FLP systems with a variety of alternative Lewis acids such as boranes, alanes, and carbon-based Lewis acids are also covered, whenever "frustration" is observed. A brief introduction of structurally related bifunctional FLPs based on borylated N-heterocycles is also included.
本综述概述了使用氮杂环卡宾（NHCs）设计和构建受阻路易斯酸碱对（FLPs）的情况。文中简要讨论了稳定的卡宾-硼烷加合物，随后详细研究了NHCs，特别是阿杜恩戈型咪唑啉-2-亚基与B(C6F5)3的反应活性。通过改变取代基和环大小对NHC进行结构和电子修饰，可得到稳定的正常加合物或FLPs，它们在没有底物的情况下会发生多种失活反应，例如通过形成异常加合物、自脱氢以及其他类型的C-H和C-F键活化。受阻程度与形成正常加合物NHC·B(C6F5)3的计算能量相关，这使得人们能够预测并合理解释它们对诸如氢气、醚、炔烃、主族元素、二氧化碳和一氧化二氮等小分子的反应活性。只要观察到“受阻”现象，还会涵盖其他基于卡宾的FLP体系，这些体系具有各种替代路易斯酸，如硼烷、铝烷和碳基路易斯酸。文中还简要介绍了基于硼化氮杂环的结构相关双功能FLPs。
