Controlled Isospecific Polymerization of α-Olefins by Hafnium Complex Incorporating with a trans-Cyclooctanediyl-Bridged [OSSO]-Type Bis(phenolate) Ligand

Treatment of trans-cyclooctanediyl-bridged [OSSO]-type ligand 1 with Hf(CH2Ph)4 in toluene afforded the corresponding hafnium(IV) dibenzyl complex 5 as pale yellow crystals. X-ray crystallographic analysis of 5 revealed that the six-coordinated hafnium center incorporated in the [OSSO]-type ligand 1 adopted cis-α configuration, and two benzyl ligands were coordinated to hafnium center by η1-fashion. In the polymerization of 1-hexene, the combination of hafnium complex 5 and B(C6F5)3, (Ph3C)[B(C6F5)4], or dMAO (dried methylaluminoxane) as an activator provided poly(1-hexene)s with perfect isotacticity ([mmmm] > 95%) and high molecular weights (Mw = 74 800–421 000 g mol–1). The combination of 5/dMAO catalyst system, in particular, exhibited fairly high activity of 2100 g mmol (5)−1 h–1, which is quite higher than those of previously reported [OSSO]-type hafnium complexes. In addition, the polymerization of 4-methyl-1-pentene (4-MP) catalyzed by the 5/(Ph3C)[B(C6F5)4] system at room temperature produced comp...

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