Catalyst system for polymerization of an olefin

The present invention relates to a catalyst system comprising a procatalyst, a co-catalyst and an external electron donor, wherein the external electron donor comprises a compound having the structure according to Formula I': Si (L)n (OR11)4-n-m(R12)m wherein, Si is a silicon atom with valency 4+; O is an oxygen atom with valency 2- and O is bonded to Si via a silicon-oxygen bond; n is 1, 2, 3 or 4; m is 0, 1, 2 or 3 n+m≤4 each R11 group is independently selected from the group consisting of linear, branched and cyclic alkyl having at most 20 carbon atoms and aromatic substituted and unsubstituted hydrocarbyl having 6 to 20 carbon atoms; each R12 group is independently selected from the group consisting of linear, branched and cyclic alkyl having at most 20 carbon atoms and aromatic substituted and unsubstituted hydrocarbyl having 6 to 20 carbon atoms; each L group is independently a group represented by the following structure, Formula II, wherein, L is bonded to the silicon atom via the nitrogen-silicon bond; L has a single substituent on the nitrogen atom, where this single substituent is an imine carbon atom; and X and Y are independently selected from the group consisting of a hydrogen atom; a heteroatom selected from group 13, 14, 15, 16 or 17 of the lUPAC Periodic Table of the Elements; a linear, branched and cyclic alkyl having at most 20 carbon atoms, optionally containing a heteroatom selected from group 13, 14, 15, 16 or 17 of the lUPAC Periodic Table of the Elements and an aromatic substituted and unsubstituted hydrocarbyl having 6 to 20 carbon atoms, optionally containing a heteroatom selected from group 13, 14, 15, 16 or 17 of the lUPAC Periodic Table of the Elements.