Understanding the M(NHC) (NHC = N-heterocyclic carbene) bond

N-heterocyclic carbenes (NHC) is a well established class of new ligands in organometallic chemistry. Their use as ligands in many reactions catalyzed by transition metal complexes has stimulated intensive research to understand the unique features of the M(NHC) bond. This review is aimed to provide an overview of the main contributions achieved by the application of advanced computational techniques.