Chemoselectivity and stereospecificity of Cr(II) catalysts for 1,3-diene polymerization

1,3-Butadiene, isoprene, (E)- and (Z)-1,3-pentadiene were polymerized with catalyst systems based on CrCl2×(dmpe)2 and Cr(CH3)2×(dmpe)2 (dmpe = 1,2-bis(dimethylphosphino)ethane) and Al(C2H5)3 or methylaluminoxane (MAO). The chemo- and stereoselectivity of these systems are strongly influenced by monomer structure. They give 1,2 syndiotactic polybutadiene, 3,4 amorphous polyisoprene, cis-1,4 isotactic poly[(E)-pentadiene] and cis-1,4 atactic poly[(Z)-pentadiene]. The factors influencing chemo- and stereoselectivity are discussed.