The present invention provides a catalyst precursor, a catalyst system comprising the precursor, and a polymerization method using the catalyst system, an embodiment of the precursor is selected from the following structures: wherein T is a bridging group; M is selected from Groups 3 to 13 atoms, and the Lanthanide series of atoms the Periodic Table of the Elements; Z is a coordination ligand; each L is a monovalent, bivalent, or trivalent anionic ligand; X and Y are each independently selected from nitrogen, oxygen, sulfur, and phosphorus; each R can be the same or different and is a bulky substituent that is sterically hindering with respect to X and Y.