The present invention provides a catalyst precursor and catalyst system comprising the precursor, an embodiment of the precursor is selected from the following structures: (I), (II), (III) and (IV) wherein T is a bridging group; M is selected from Groups 3 to 7 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; R is a non-bulky substituent that has relatively low steric hindrance with respect to X; and R' is a bulky substituent that is sterically hindering with respect to Y.