N-heterocyclic carbenes have been used as ligands for metals compounds that are function as catalysts to perform a variety of organic chemical transformations. These catalysts have been used in olefin metathesis, cross coupling reactions to form C-C or C-N bonds, and in hydrogenations of ketones and alkenes as well as other miscellaneous reactions. The N-heterocyclic ligands have improved the yields of these reactions as well as increased their scopes. Many research groups around the world have become interested N-heterocyclic carbenes as ligands for catalysts which has resulted in the rapid development of the ligands and the catalysts that use them. It is possible that the N-heterocyclic ligands will replace phosphine ligands in a variety of catalyst systems
