Organometallic compounds heterocyclic carbenes

Carbene transfer reactions with participation of organometallic compounds bearing heterocyclic substituents 99CSR315. 

Af-Heterocyclic carbenes and phosphine ligands can bind metal centers in a somewhat similar feshion via dative coordination using a lone pair of electrons. Therefore, phosphines are often considered to be the closest neighbors to NHCs in terms of organometallic chemistry. However, the properties of these two classes of compounds can be quite different, and can yield, for example, catalysts with quite different reactivity. The use of NHCs in olefin metathesis [25] and in palladium catalysis [26], for example, has allowed the preparation of highly active and stable species that are now at the forefront of their fields. Various studies have been conducted to explore the nature of bonding between NHCs and metal centers. Diez-Gonzalez and Nolan reviewed some aspects of NHC coordination to metal centers in 2007 [27]. 

Due to the ability of imidazolium compounds to form metallic Af-heterocyclic carbene complexes, imidazolium-based ionosilicas have widely been studied for the formation of silica-supported NHC species and found wide applications in organometallic catalysis. However, ionic species recently found to promote a large variety of reactions due to their ionic nature. Cooperative nucleophilic-electrophilic activation is a widely accepted concept in catalysis, and due to their ionic nature, ionic liquid should be considered as bifunctional catalysts. 

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