N-Heterocyclic Carbenes as Ligands for Olefin Metathesis Catalysts

Abstract

Olefin metathesis is a powerful tool to form carbon—carbon double bonds in organic and polymer chemistry. The introduction of N-heterocyclic carbenes as ligands for ruthenium catalysts led to an impressive evolution in olefin metathesis. Indeed, the NHC—ruthenium complexes (second generation) display higher activity and reactivity compared to the parent phosphine-based complexes (first generation). In this chapter the improvements of the second generation catalysts will be illustrated. We will further present a brief discussion of the mechanism and the synthesis of NHC-containing olefin metathesis catalysts. In the final part, a survey of currently available second generation catalysts will be discussed with a particular emphasis on structural modifications of the NHC ligand.