Abstract: The invention relates to a polymerization catalyst system comprising a catalytic complex formed by activating a transition metal compound which comprises a metal selected from group 3 through 10 of the periodic table, preferably from group 4, 5, or 6 of the periodic table, and a group 13, 15, or 16 heterocyclic fused cyclopentadienide ligand. In one embodiment the inventive transition metal compound is represented by the [L]mM[A]n(S)o wherein M is a transition metal selected from groups 3 through 10 of the periodic table, and at least one of L is group 13, 15, or 16 heterocyclic fused cyclopentadienide ligand. Also disclosed is a polymerization process utilizing the catalyst systems of the invention. Ethylene polymerizations or copolymerizations with dimethyl (&eegr;5-pentamethylcyclopentadienyl)(1-azaindenyl) zirconium and bis(5-methyl-cyclopenta[b]thiophene) zirconium dichloride, activated by tris(pentafluorophenyl) boron and methylalumoxane, respectively, are illustrated.

Abstract: The invention encompasses late transition metal catalyst systems and their use in polymerization processes, particularly in solution, 2-phase suspension and super-critical phase polymerization of ethylene-containing polymers. Preferred embodiments include the use of a late transition metal catalyst system comprising a Group 8, 9, 10, or 11 metal complex stabilized by a bidentate ligand structure for polymerization under elevated ethylene pressure, or concentration, conditions.