Metal alkyl-arene having general formula (I) or (Ia): M (η6-arene)2AlqXrRs (I) M (η6-arene)AlqXrRs (Ia) wherein: —M represents zirconium (Zr), hafnium (Hf), or mixtures thereof, preferably zirconium; —arene represents a benzene, or a benzene 10 substituted with from 1 to 6 linear or branched C1-C6 alkyl groups, or mixtures thereof; —X represents a halogen atom selected from chlorine, bromine, fluorine, iodine, preferably chlorine; —R represents a linear or branched C1-C15 alkyl group; —q is a number ranging from 2 to 6, preferably 3 for a metal alkyl-arene having general formula (I), 2 for a metal alkyl-arene having general formula (Ia); —r is a number ranging from 1 to 20, preferably 9 for a metal alkyl-arene having general formula (I), 6 for a metal alkyl-arene having general formula (Ia); —s is a number ranging from 1 to 6, preferably 2. Said metal alkyl-arene can be advantageously used for the preparation of solid components of catalysts for the (co)polymerization of α-olefins.