Coinage Metal Complexes of Chiral N-Heterocyclic Carbene Ligands: Syntheses and Applications in Asymmetric Catalysis

Chiral N-heterocyclic carbenes (NHCs) have become ligands of choice due to their remarkable catalytic activity in organic transformation reactions. Combining the chiral NHC ligand family and coinage metals became a productive area of research. The organometallic chemistry of coinage metals with the chiral N-heterocyclic carbene (NHC) ligands is reviewed, with a special emphasis on the synthesis, characterization and possible applications obtained. Significant sections are devoted to the various recently developed coinage metal-chiral NHC complexes and a detailed comparison of their activities which aims to rationalize the structure-activity relationships. Various methods of preparations of coinage metal-chiral NHC complexes along with some typical examples of reactivity and mechanisms are covered. Cu-chiral NHC complexes involved in conjugated additions, allylic substitutions, boration of alkenes, hydrosilylation of ketones and formation of alkenes are covered, along with some remarkable examples and reactivity of Ag-chiral NHC complexes. Finally, applications of Au-chiral NHC complexes in the asymmetric cyclization of ester-functionalized 1,6-enynes, 1,6-enyneamines and substituted propargyloxymethanes are also reviewed.