Polymerization of 1,3-Butadiene with Catalysts Based on Cobalt Dichloride Complexes with Aminophosphines: Switching the Regioselectivity by Varying the MAO/Co Molar Ratio

Several novel cobalt dichloride complexes with amino-phosphine bidentate ligands were synthesized and characterized. For some of them single crystals were obtained and their molecular structure was determined by X-ray diffraction method. All the complexes were then used in combination with MAO for the polymerization of 1,3-butadiene, obtaining polymers with different structures (i.e., predominantly 1,2 or cis-1,4) mainly depending on the type of ligand and on the MAO/Co molar ratio. The behavior of these novel catalysts was compared with that exhibited, in the polymerization of the same monomer, by the systems CoCl2(PR3)2-MAO and CoCl2(PRPh2)2-MAO (R = alkyl or cycloalkyl group), and by the systems based on cobalt dichloride complexes with various bi- and tridentate ligands (e.g., diphosphines, bis-imines, pyridyl-imines, bis-iminopy- ridines). The comparison between the different systems allowed us to make some clarity about the actual and effective role played by the various types of ligands in the polymerization of conjugated dienes with catalytic systems CoCl2(L)-MAO, in which L = mono-, bi-, or tri-dentate ligand.