Novel bridged bis-azulenyl and bis-tetrahydroazulenyl hafnocenes: Synthesis, structure, and propylene polymerization behavior

Novel bridged bis-azulenyl hafnocenes: dichlorodimethylsilylenebis(2-methyl-4-phenyl-4H-azulenyl) hafnium (4a) and dichlorodimethylsilylenebis[2-ethyl-4-(4-chlorophenyl)-4H-azulenyl] hafnium (4b) were synthesized from 2-methylazulene and 2-ethylazulene, respectively. Hydrogenation of 4a and 4b gave novel bis-tetrahydroazulenyl hafnocenes: dichlorodimethylsilylenebis(2-methyl-4-phenyl-4H-5,6,7,8-tetrahydroazulenyl) hafnium (5a) and dichlorodimethylsilylenebis[2-ethyl-4-(4-chlorophenyl)-4H-5,6,7,8-tetrahydroazulenyl] hafnium (5b). The structures of 4a and 5b were determined by X-ray crystallographic analysis to fold C2 symmetry. These hafnocenes were found to be active catalysts for propylene polymerization in the presence of methylaluminoxane (MAO), and the preliminary polymerization behavior of these catalysts was evaluated. The melting point and molecular weight of resultant polypropylene were higher than those of the bis-azulenyl zirconocenes. In particular, a high melting point (160 °C for 5a and 161 °C for 5b) was observed with the bis-tetrahydroazulenyl system, although the activities by these hafnocenes were lower than those by the corresponding zirconocenes.