Mesoionic carbenes are a subclass of the family of N-heterocyclic carbenes that generally feature less heteroatom stabilization of the carbenic carbon and hence impart specific donor properties and reactivity schemes when coordinated to a transition metal. Therefore, mesoionic carbenes and their complexes have attracted considerable attention both from a fundamental point of view as well as for application in catalysis and beyond. As a follow-up of an earlier Chemical Reviews overview from 2009, the organometallic chemistry of N-heterocyclic carbenes with reduced heteroatom stabilization is compiled for the 2008–2017 period, including specifically the chemistry of complexes containing 1,2,3-triazolylidenes, 4-imidazolylidenes, and related 5-membered N-heterocyclic carbenes with reduced heteratom stabilization such as (is)oxazolylidenes, pyrrazolylidenes, and thiazolylidenes, as well as pyridylidenes as 6-membered N-heterocyclic carbenes with reduced heteroatom stabilization. For each ligand subclass, metalation strategies, electronic and steric properties, and applications, in particular, in metal-mediated catalysis, are compiled. Mesoionic carbenes demonstrate particularly high activity in (water) oxidation, hydrogen transfer reactions, and cyclization reactions. Unique features of these ligands are identified such as their dipolar structure, their specific donor properties, as well as stability aspects of the ligand and the complexes, which provides opportunities for further research.

中文翻译：

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中离子和相关的杂原子稳定的N-杂环碳烯络合物：合成，催化和其他应用程序。

中离子碳烯是N-杂环碳烯家族的一个子类，通常具有较低的碳碳杂原子稳定度，因此与过渡金属配位时可赋予特定的供体性质和反应性。因此，从基本的观点以及在催化中及其他方面的应用而言，中离子卡宾及其复合物已引起相当大的关注。作为早期化学审查的后续措施从2009年的概述开始，对杂原子稳定度降低的N-杂环卡宾的有机金属化学进行了2008-2017年的汇编，其中特别包括含有1,2,3-三唑基，4-咪唑基和相关的5元N的配合物的化学。杂原子稳定度降低的β-杂环卡宾，如（is）恶唑基，吡唑基亚烷基和噻唑基，以及吡啶基作为六元N-杂环卡宾，具有降低的杂原子稳定性。对于每个配体子类，特别是金属化策略，电子和空间特性及其应用，特别是在金属介导的催化作用中，都得到了汇编。中离子卡宾在（水）氧化，氢转移反应和环化反应中表现出特别高的活性。