Cationic allenylidene ruthenium complexes, [Ru=C=C=CPh2(L)(p-cymene)]PF6 (L = PCy3, 1,3-dimesityl-4,5-dihyroimidazol-2-ylidene) are implemented as versatile catalyst for the controlled atom transfer radical polymerization of vinylmonomers and deliver high molecular weight polymers with. a quite narrow molecular weight distribution. Improvements on the activity can be made by adding additives or transforming the. allenylidene entity into a corresponding Fischer carbene.