N-heterocyclic carbenes (NHCs) are a widely used class of ligands that have enabled an exciting variety of organometallic chemistry and catalysis. As researchers design and customize these ligands for specific applications, various design concepts have emerged. This review covers several of these design concepts and their impact on and promise for organometallic chemistry and catalysis. These concepts are bulky ligands that remain flexible for substrate binding and reactivity, ring-expanded NHCs with different steric and electronic properties, NHCs appended to supramolecular assemblies that control the microenvironment around the metal center; and NHCs with pendant labile functional groups.

N-杂环卡宾（NHCs）是一类广泛使用的配体，可实现各种令人兴奋的有机金属化学和催化作用。随着研究人员针对特定应用设计和定制这些配体，出现了各种设计概念。这篇综述涵盖了这些设计概念中的几个及其对有机金属化学和催化的影响和前景。这些概念是体积庞大的配体，它们对于底物的结合和反应仍然保持柔性，具有不同的空间和电子特性的环膨胀NHC，附着在控制金属中心周围微环境的超分子组装体上的NHC；和带有不稳定侧基的NHC。