he cyclopentadienyl ring associated therewith can be joined together to form a ring containing from 4 to about 20 carbon atoms, R3 is a bridging group, n is 0 or 1, Y is a heteroatom-containing ligand in which the heteroatom is coordinated to M, M is a transition metal having a valence of from 3 to 6, each X is a non-cyclopentadienyl ligand and is, independently, halogen or a hydrocarbyl, oxyhydro