Group 4 metallocenes useful as catalysts for the polymerization of olefins

A complex of formula (I): wherein M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from -R' 2 C-, -R' 2 C-CR' 2 -, -R' 2 Si-, -R' 2 Si-SiR' 2 -, -R' 2 Ge-, wherein each R' is independently a hydrogen atom, C1-C20-hydrocarbyl, tri(C1-C20-alkyl)silyl, C6-C20-aryl, C7-C20-arylalkyl or C7-C20-alkylaryl; each R 1 is a C4-C20 hydrocarbyl radical branched at the ²-atom to the cyclopentadienyl ring, optionally containing one or more heteroatoms belonging to groups 14-16, or is a C3-C20 hydrocarbyl radical branched at the ²-atom to the cyclopentadienyl ring where the ²-atom is an Si-atom; n is 0-3; each R 18 is the same or different and may be a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms belonging to groups 14-16; each R 4 is a hydrogen atom or a C 1-6 -hydrocarbyl radical; each W is a 5 or 6 membered aryl or heteroaryl ring wherein each atom of said ring is optionally substituted with an R 5 group; each R 5 is the same or different and is a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms belonging to groups 14-16; and optionally two adjacent R 5 groups taken together can form a further mono or multicyclic ring condensed to W optionally substituted by one or two groups R 5 .