A complex of formula (I) wherein M is zirconium or hafnium; each X independently is a sigma ligand; L is a divalent bridge selected from —R′2C—, —R′2C—CR′2—, —R′2Si—, —R′2Si—SiR′2—, —R′2Ge—, wherein each R′ is independently a hydrogen atom or a C1-C20-hydrocarbyl .group optionally containing one or more silicon atoms or heteroatoms of Group 14-16 of the periodic table or fluorine atoms, and optionally two R′ groups taken together can form a ring; R2 and R2′ are each independently a C1-C20 hydrocarbyl group, —OC1-20 hydrocarbyl group or —SC1-20 hydrocarbyl group; R5 is a —OC1-20 hydrocarbyl group or —SC1-20 hydrocarbyl group, said R5 group being optionally substituted by one or more halo groups; R5′ is hydrogen or a C1-20 hydrocarbyl group; —OC1-20 hydrocarbyl group or —SC1-20 hydrocarbyl group; said C1-20 hydrocarbyl group being optionally substituted by one or more halo groups; R6 and R6′ are each independently a C1-20 hydrocarbyl group; —OC1-20 hydrocarbyl group or —SC1-20 hydrocarbyl group; each R1 and R1′ are independently —CH2Rx wherein Rx are each independently H, or a C1-20 hydrocarbyl group, optionally containing heteroatoms.