Ruthenium Complexes Bearing N-Heterocyclic Carbene (NHC) Ligands

The vast family of ruthenium complexes with nucleophilic N-heterocyclic carbene (NHC) ligands is selectively discussed as an improved alternative to their parent diphosphane ruthenium counterparts previously applied in olefin metathesis reactions. The survey covers work done to-date on the ruthenium alkylidene, vinylidene, allenylidene and indenylidene complexes bearing imidazolin-2-ylidene and dihydroimidazolin-2-ylidene carbenes, as well as a number of immobilised ruthenium complexes having these types of ligands. Examples of chiral compounds complete the spectrum of NHC ruthenium complexes. Synthetic methods, catalytic properties and application profile in ring-closing metathesis, cross metathesis, ring-opening metathesis and metathesis polymerisation are highlighted.