Transitiemetal complexes with N-heterocyclic carbene ligands (NHC or imidazolidine) are known for a long time, only recently one discovers the possibilities of this group of ligands. Variation of the substituents on the N-atoms serves to change the electronic and steric properties of the NHC-ligands. Applying this opportunity in the field of homogeneous catalysis will result into "tunned" catalysts depending on the reaction conditions. Another strength of the NHC-ligands is the variety of metal centra which can be used to coordinate. Several new immobilisation techniques becomes possible now. Not only immobilisation on an inert support (organic or inorganic) but also anchoring in ionic solvents.