Department of Chemistry, Fudan University, Shanghai 200433, China.
Chem Soc Rev. 2015 Apr 7;44(7):1898-921. doi: 10.1039/c4cs00441h. Epub 2015 Jan 22.
Since the discovery of a stable N-heterocyclic carbene (NHC), the use of NHCs in chemistry has developed rapidly over the past two decades. These interesting compounds are predominantly employed in organometallic chemistry as ligands for various metal centers, and as organocatalysts for a variety of transformations. In particular, the NHC transition metal complexes have received widespread attention, and significant progress has been made in the development of group 4 NHC-complexes in the last few years. These group 4 NHC-complexes are of interest because of their unique structural properties, and their potential application in organic transformations and catalysis. This review covers the superior design strategies for NHC ligands to stabilize early transition metals and well-defined group 4 metal complexes with mono- and multi-dentate NHC ligands. In this context, four types of NHC-complexes, i.e., carbon-functionalized NHCs, nitrogen-functionalized NHCs, oxygen-functionalized NHCs and nitrogen/oxygen-functionalized unsymmetric NHCs, are described. In addition, the use of group 4 NHC-complexes as catalysts in olefin (co)polymerization, ring-opening polymerization of rac-lactide, copolymerization of epoxides and CO2, as well as hydroamination/cyclization of aminoalkenes, is presented. Furthermore, limitations and challenges are discussed.
自稳定 N-杂环卡宾（NHC）被发现以来，NHC 在过去二十年中的化学应用得到了快速发展。这些有趣的化合物主要被用作各种金属中心的配体在金属有机化学中，以及作为各种转化的有机催化剂。特别是，NHC 过渡金属配合物受到了广泛关注，近年来在开发第 4 族 NHC 配合物方面取得了重大进展。这些第 4 族 NHC 配合物因其独特的结构性质及其在有机转化和催化中的潜在应用而受到关注。本综述涵盖了用于稳定早期过渡金属和具有单齿和多齿 NHC 配体的定义明确的第 4 族金属配合物的 NHC 配体的优越设计策略。在这种情况下，描述了四种类型的 NHC 配合物，即碳功能化 NHC、氮功能化 NHC、氧功能化 NHC 和氮/氧功能化不对称 NHC。此外，还介绍了第 4 族 NHC 配合物作为催化剂在烯烃（共）聚合、rac-丙交酯开环聚合、环氧化物和 CO2 共聚以及氨基烯烃的氢胺化/环化中的应用。此外，还讨论了局限性和挑战。
