Coordination chemistry of ditopic carbanionic N-heterocyclic carbenes

• A comprehensive review of the chemistry of ditopic carbanionic N-heterocyclic carbenes (dcNHCs) is provided.
• The isolation of dcNHCs as alkali-metal salts is described.
• The reactivity of alkali metal salts of dNHCs is reviewed.

The chemistry of N-heterocyclic carbenes, particularly imidazol-2-ylidenes, has been exhaustively documented in the literature. Amongst the many bond activation reactions available for such species (CH, CC and NC), it has recently become apparent that deprotonation of the alkenic backbone can give rise to ditopic carbanionic carbenes, i.e. anionic species capable of bonding to Lewis acidic centres via two different carbon sites (C2 and C4 or C4 and C5). In this article, we aim to provide a comprehensive review of the chemistry of such species, with a particular focus on their isolation as alkali-metal salts and their subsequent reactivity.

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