Synthesis of Metal N-Heterocyclic Carbene Complexes

N-heterocyclic carbene ligands(NHCs) are playing an increasingly important role in many areas such as organometallic, organic synthetic, pharmaceutical and polymer chemistry While numerous powerful catalytic systems incorporating NHC ligands have been described, methods of synthesizing them have advanced more slowly This review describes the recent progress of the methods used in the preparation of N-heterocyclic carbene complexes According to the nature of the NHC precursor and to the activation method employed, the common routes for preparing NHC-metal complexes are insertion of metal ions Into the carbon-carbon double bonds of highly electron-rich alkenes, coordination of preformed, isolated free carbenes, deprotonation of an Imidazolium salt with an external base or with metal complex having a basic ligand, thermal decomposition of corresponding carbene adducts, transmetallation from a silver-NHC complex or from a gold-NHC complex, oxidative addition of the C2-X (X = Me, halogen, H) bond of an imidazolium precursor In addition, our research group firstly found that iron, cobalt, nickel, and copper complexes of N-heterocyclic carbenes can be directly synthesized by using commercially available metal powders