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 g·mmol(−1). When the Dmp-substituted pre-catalyst 10/dMAO system was used, the highest activity, over 7700 g·mmol(10)(−1)·h(−1), was recorded involving the formation of precisely isospecific polystyrenes of [mm] more than 99%.