Highly Active and Isospecific Styrene Polymerization Catalyzed by Zirconium Complexes Bearing Aryl-substituted [OSSO]-Type Bis(phenolate) Ligands

[OSSO]-type dibenzyl zirconium(IV) complexes 9 and 10 possessing aryl substituents ortho to the phenoxide moieties (ortho substituents, phenyl and 2,6-dimethylphenyl (Dmp)) were synthesized and characterized. Upon activation with dMAO (dried methylaluminoxane), complex 9 was found to promote highly isospecific styrene polymerizations ([mm] = 97.5%-99%) with high molecular weights M-w up to 181,000 gmmol(-1). When the Dmp-substituted pre-catalyst 10/dMAO system was used, the highest activity, over 7700 g<bold>mmol</bold>(10)(-1)h(-1), was recorded involving the formation of precisely isospecific polystyrenes of [mm] more than 99%.