Abstract: A catalyst system comprising a) a metal complex of the formula CyLMZp, wherein M is a group 4 metal Z is an anionic ligand, p is number of 1 to 2, preferably 2 Cy is a cyclopentadienyl-type ligand and, L is a ligand of the formula wherein each A is independently selected from the group consisting of nitrogen and phosphorus and R1, R2, and R4 are independently selected from the group consisting of hydrogen, unsubstituted or substituted hydrocarbyl, unsubstituted or substituted silyl and unsubstituted or substituted germyl residues, and b) a boron containing activator, characterized in that the molar ratio of the boron of the activator to M of the metal complex is greater than 2.5.