Synthesis, Structure, and Polymerization Behavior of Bridged Zirconocenes Bearing Seven-Membered Rings

Bridged zirconocenes bearing seven-membered rings dichlorodimethylsilylenebis(2-methyl-4-phenyl-4-H-azulenyl)zirconium (3a) and dichlorodimethylsilylenebis(2-methyl-4-phenyl-4-H-5,6,7,8-tetrahydroazulenyl)zirconium (4) were synthesized. A silylene-bridged ligand was obtained by the reaction of 2-methylazulene, phenyllithium, and dichlorodimethylsilane. After lithiation of the ligand by n-butyllithium, reaction with zirconium tetrachloride gave a rac and meso mixture of 3. The structure was confirmed by X-ray crystallographic analysis. It was found that both of the phenyl groups at the 4-position are oriented outside toward the metal center and the seven-membered ring is not planar. Furthermore, reaction with hydrogen in the presence of platinum oxide gave 4. When activated with methylaluminoxane, these complexes showed high catalytic activity for polymerization of propene to give isotactic polypropylene.