During the last decades an enormous advancement has been made in the design and synthesis of "well-defined' or "single-site" catalysts for the polymerization of olefins. The majority of these catalysts belong to the metallocene ensemble, although some are known that contains one cyclopentadienyl ring and (for example) a pendant amido ligand. Complexes containing many other functionalities including chelating diamido or chelating benzamidinate ancillary ligands have received attention as potential Ziegler-Natta catalysts. 

We have investigated the α-olefin polymerization chemistry catalyzed by several group 4 bis(benzamidinate) complexes. We have shown that we are able to tune the stereoregularity of various polymers just by changing the monomer concentration during the polymerization to obtain elastomers. In addition, we will show unique imidazoline-2-iminato complexes allowing to reduce the amount of the cocatalyst (MAO=methylalumoxane) to impressive values. The presentation will also show recent results with new systems.