Halogenated organometallic complexes and their use in the polymerization of unsaturated monomers

Process for the preparation of organometallic complexes comprising lanthanides, represented by the general formula,

• Me(Ar)(AlX.sub.3 R).sub.3 (I)
• comprising the steps of:
• (a) forming a suspension of a complex of the general formula:
• Me (Ar)(AlX.sub.4).sub.3 (II)
• in a solvent, said solvent being aromatic, aliphatic, or cyclo-alyphatic, and maintaining the temperature at room temperature;
• (b) adding a solution of a compound of formula:
• AlR.sub.3 (III)
• in same said solvent wherein:
• Me represents a metal of group IIIA, having atomic number 21, 39, or an atomic number of between 57 and 71,
• Ar represents benzene or a benzene substituted with from 1 to 3 alkyl groups containing from 1 to 10 carbon atoms,
• X is a halogen atom, whereas,
• R is a linear, cyclic or branched alkyl radical containing from 1 to 12 carbon atoms,
• and in such a quanity that the molar ratio (III)/(II)=1.5, and reacting at room temperature until the complete dissolution of the suspended solid (II).