A metallocene complex of a metal of group 4 of the periodic table having the following formula: wherein: - M is a metal selected from titanium, zirconium and hafnium, coordinatively bonded to a first η 5 -cyclopentadienyl group; - R' represents an unsaturated hydrocarbyl group; - R" represents an optional group anionically bonded to the metal M, consisting of an organic or inorganic radical, different from cyclopentadienyl or substituted cyclopentadienyl; - the groups R 1, R 2, R 3, R 4 and R 5, each independently represent, an atom or radical bonded to said first η 5 - cyclopentadienyl group, and is selected from hydrogen or a suitable organic or inorganic substituent of said cyclopentadienyl group; - R 6 represents a suitable organic or inorganic group, anionically bonded to the metal M; - "w" has the value of 0 or 1, depending on whether the R" group is absent or present in formula; characterized in that said R' group consists of an unsaturated oligomeric group having the following formula: -(A x D y U z)R I wherein: - A represents any monomeric unit deriving from a vinylaromatic group polymerizable by means of anionic polymerization, having from 6 to 20 carbon atoms; - D represents any monomeric unit deriving from a conjugated diolefin polymerizable by means of anionic polymerization, having from 4 to 20 carbon atoms; - U represents any generic optional monomeric unit deriving from an unsaturated compound copolymerizable with any of the above conjugated di-olefins D or vinylaromatic compounds A; - R I represents an aliphatic, cycloaliphatic, aromatic or alkyl aromatic group having from 1 to 20 carbon atoms; - each index "x" and "y" can be independently zero or an integer, provided the sum (x+y) is equal to or higher than 2; - "z" can be zero or an integer ranging from 1 to 20; with the proviso that, when R 6 is a η 5 -cyclopentadienyl or substituted η 5 -cyclopentadienyl group and R' is -(A x)R I, R" is different from -(A x)R I. - M is a metal selected from titanium, zirconium and hafnium, coordinatively bonded to a first η 5 -cyclopentadienyl group; - R' represents an unsaturated hydrocarbyl group; - R" represents an optional group anionically bonded to the metal M, consisting of an organic or inorganic radical, different from cyclopentadienyl or substituted cyclopentadienyl; - the groups R 1, R 2, R 3, R 4 and R 5, each independently represent, an atom or radical bonded to said first η 5 - cyclopentadienyl group, and is selected from hydrogen or a suitable organic or inorganic substituent of said cyclopentadienyl group; - R 6 represents a suitable organic or inorganic group, anionically bonded to the metal M; - "w" has the value of 0 or 1, depending on whether the R" group is absent or present in formula; characterized in that said R' group consists of an unsaturated oligomeric group having the following formula: -(A x D y U z)R I - A represents any monomeric unit deriving from a vinylaromatic group polymerizable by means of anionic polymerization, having from 6 to 20 carbon atoms; - D represents any monomeric unit deriving from a conjugated diolefin polymerizable by means of anionic polymerization, having from 4 to 20 carbon atoms; - U represents any generic optional monomeric unit deriving from an unsaturated compound copolymerizable with any of the above conjugated di-olefins D or vinylaromatic compounds A; - R I represents an aliphatic, cycloaliphatic, aromatic or alkyl aromatic group having from 1 to 20 carbon atoms; - each index "x" and "y" can be independently zero or an integer, provided the sum (x+y) is equal to or higher than 2; - "z" can be zero or an integer ranging from 1 to 20; with the proviso that, when R 6 is a η 5 -cyclopentadienyl or substituted η 5 -cyclopentadienyl group and R' is -(A x)R I, R" is different from -(A x)R I.