High Oxidation State Transition Metal Complexes Ligated with N-Heterocyclic Carbenes

N-heterocyclic carbenes (NHCs) found numerous applications as ligands for transition metal complexes during the last two decades. Only recently, however, increasing attention is turning to high oxidation state organometallics with NHC ligands. A surprising number of stable complexes of that type have been described mainly during the last five years and several of them have potential for application in both homogeneous and heterogeneous catalysis of organic reactions. This article describes the preparation and characteristics of these high oxidation state organometallic complexes with NHC ligands and gives an outlook on their possible applications. Keywords: N-heterocyclic carbenes (NHCs), NHC ligands, transition metal complexes, organometallics, heterogeneous catalysis, oxidation state