Polymerization of 1,3-dienes with iron complexes based catalysts. Influence of the ligand on catalyst activity and stereospecificity

Various iron dichloride complexes with aliphatic and aromatic bidentate amine ligands have been synthesized and used, in combination with aluminium-compounds (AlR3 or methylaluminoxane), for the polymerization of 1,3-dienes. Catalyst activity, chemo- and stereoselectivity are strongly influenced by the type of ligand; systems based on iron complexes with aromatic bidentate amines (e.g. bypiridine or phenantroline), in particular, exhibit an extremely high activity, giving from butadiene a 1,2 syndiotactic polymer. These systems are also able to polymerize substituted butadienes (e.g. isoprene, (E)-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene) giving polymers with different structure from the different monomers; these results have permitted to confirm some aspects of the polymerization mechanism previously proposed.