Polymerization of 1,3-butadiene catalyzed by Co(ii) and Ni(ii) complexes of 6,6′-dihydroxy-2,2′-bipyridine ligands: 1,4-cis-polymerization versus isospecific 1,2-polymerization†

Abstract

Co and Ni complexes having the 6,6′-dihydroxy-2,2′-bipyridine (DHBP) ligand [CoCl₂(dhbp), NiBr₂(dhbp)] in the presence of organoaluminum cocatalysts showed much higher catalytic activity in 1,3-butadiene polymerization than the complexes having the 2,2′-bipyridine or 6,6′-dimethoxy-2,2′-bipyridine ligand without hydroxy groups. The polybutadienes obtained had 1,4-cis structure (up to 94.6%). In contrast, addition of 5-norbornene-2-methyl amine in 1,3-butadiene polymerization catalyzed by NiBr₂(dhbp)/methylaluminoxane (MAO) caused a marked change in the microstructure of the polybutadiene to the iso-1,2-structure with high chemo- and stereoselectivities (mm > 99%).