Ruthenium-Based Heterocyclic Carbene-Coordinated Olefin Metathesis Catalysts

Nearly 400 ruthenium heterocyclic carbene-corodinated olefin metathesis catalysts were prepared, which offer a wide array of structures and activities that will benefit specific applications such as aqueous and asymmetric reactions. Carbenes are strong Lewis bases, acting as excellent s-donors and poor π-acceptors, and afford metal-carbon bonds that are usually less labile than the related metal-phosphine bonds. In 1998, Herrmann and co-workers reported the synthesis of the first heterocyclic carbene-containing ruthenium-based metathesis catalysts in which both phosphine ligands were replaced by NHC (N-heterocyclic carbene). In another significant contribution to the field of ruthenium based metathesis, the Hoveyda group reported the synthesis of isopropoxystyrene-coordinated catalyst. The general reactivity can be understood in terms of the effect of a ligand on the initiation formation of the 14-electron species and the turnover of the olefin complex.