An overview of N-heterocyclic carbenes

N-heterocyclic carbenes are powerful tools in organic chemistry, with many commercially important applications; this overview describes their properties and potential uses. N-heterocyclic carbenes are cyclic molecules that contain one carbene and at least one nitrogen atom within the carbene-containing ring structure. These molecules are widely used as ancillary ligands for the preparation of transition-metal-based catalysts and can be highly active organocatalysts in their own right. For these reasons, they have been used in a broad range of synthetic organic chemistry applications, including commercially important processes. In this Review, the authors provide a concise overview of N-heterocyclic carbene chemistry, summarizing their general structure and chemical properties, and then highlighting how the unique reactivity of these molecules has been used in a broad range of interesting organic and organometallic transformations. The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.