Catalyst system for producing polyethylene copolymers in a high temperature solution polymerization process

Catalyst system for producing ethylene copolymers in a high temperature solution process, the catalyst system comprising (i) a metallocene complex of formula (I), M is Hf or a mixture with Zr, provided that more than 50% by moles of the complex of Formula I has M=Hf, X is a sigma ligand, R are the same or different from each other and can be saturated linear or branched C1-C10 alkyl, C5-C10 aryl, C6-C20 alkylaryl or C6-C20 arylalkyl groups, which can optionally contain up to 2 heteroatoms or silicon atoms, R1 is a C6-C20-aryl, which can be unsubstituted or substituted by one or up to 5 linear or branched C1-C10 alkyl group(s), R2 is a saturated linear or cyclic C3-C20 alkyl group or a branched CR3R4R5 group, wherein R3 is hydrogen or an C1-C20 alkyl group and R4 and R5 are the same or are different and can be an C1-C20 alkyl group and (ii) a boron containing cocatalyst.