N-Heterocyclic Carbenes

Product name: N-Heterocyclic Carbenes

Product Description:
N-Heterocyclic carbenes NHC are stable singlet carbenes that can act as excellent two electron donor ligands towards almost any element in the periodic table. They coordinate strongly to late transition metals and heavy main group elements, but are also known to bind to early transition metals and the lanthanoids.

NHC derive their excellent stability from their unique electronic structure. The carbene carbon atom is sp 2-hybridised featuring two σ-bonds to the adjacent nitrogen atoms ("pull" stabilisation due to large electronegativity of nitrogen) and an electron lone pair in the remaining sp 2-hybrid orbital. Two π N → π C donor interactions from the electron lone pairs on nitrogen into the "empty" p-orbital of the carbene carbon atom complete the electron configuration on the carbene carbon atom ("push" stabilisation) and gives the NHC its stability.

Product Application: Since the by far most common application of NHC ia as ligands in homogenous catalysis, methods for the preparation of the respective precatalyst complexes have been devised. They comprise i) synthesis of the free carbene and subsequent coordination to the metal, ii) in situ deprotonation of imidazolium in the presence of a metal complex, iii)reaction of the imidazolium salt with Ag 2O to form the silver NHC complex and subsequent carbene transfer to the desired metal fragment, iv) reaction of the imidazolium salt with a basic metal salt (i.e. an acetate).