Chiral ligands play a central role in enantioselective transition-metal catalysis. The success of achiral N-heterocyclic carbenes (NHCs) as stable electron-rich neutral ligands in homogeneous catalysis led to the development of a manifold of chiral NHCs as stereodirecting ancillary ligands for various enantioselective transformations. Due to the modular design of NHCs and the ease of access to their azolium salt precursors, tailor-made NHCs are readily available. Many chiral NHC scaffolds have been synthesised and tested in catalysis. Herein, we highlight only those NHC structures which have enabled high degrees of enantioselectivity in transition-metal catalysis. Following a brief introduction to the field of chiral NHCs, this tutorial review introduces different categories of chiral NHCs and provides a guide to the structural fine-tuning of ligand requirements and stereochemical models.

中文翻译：

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用于不对称过渡金属催化的特权手性N-杂环卡宾配体

手性配体在对映选择性过渡金属催化中起核心作用。非手性N-杂环卡宾（NHCs）作为稳定的富电子中性配体在均相催化中的成功导致了手性NHC的流形化作为各种对映选择性转化的立体定向辅助配体的发展。由于NHC的模块化设计以及易于获得其偶氮盐前体的优势，因此可以轻松获得量身定制的NHC。已经合成了许多手性NHC支架并进行了催化测试。本文中，我们仅重点介绍那些在过渡金属催化中具有高度对映选择性的NHC结构。在简要介绍了手性NHC领域之后，