Heteroligated Hafnium Complexes with Enhanced Activity and Thermal Stability toward Olefin (Co)polymerization

Three heteroligated Hf metal complexes, [C₅H₄N-CH(Me)-N-2,6-R¹-C₆H₃][C₆H₅-N-C₆H₄-S-R²]HfMe₂ (for <b>Hf1/3</b>, R¹ = ^<i>i</i>Pr and R² = Me; for <b>Hf2/3</b>, R¹ = Me and R² = Me; for <b>Hf2/4</b>, R¹ = Me and R² = Ph), have been prepared from orthogonal reactions between pyridyl-amido Hf complexes [C₅H₄N-CH(Me)-N-2,6-R¹-C₆H₃]HfMe₃ (for <b>Hf1</b>, R¹ = ^<i>i</i>Pr; for <b>Hf2</b>, R¹ = Me) and thioether-amido ligands C₆H₅-N-C₆H₄-S-R² (for <b>L3</b>, R² = Me; for <b>L4</b>, R² = Ph) and employed for olefin (co)polymerization. For comparison, homoligated metal analogue [C₆H₅-N-C₆H₄-S-Me]₂HfMe₂ (<b>Hf3/3</b>) was also prepared. In ethylene homopolymerization, heteroligated metal complexes (<b>Hf1/3</b>, <b>Hf2/3</b>, and <b>Hf2/4</b>) exhibited higher activity and better thermal stability than monoligated and homoligated metal analogues (<b>Hf1</b>, <b>Hf2</b>, and <b>Hf3/3</b>). In particular, <b>Hf1/3</b> showed an activity as high as 2.82 × 10⁷ g of polymer (mol of Hf)^-1 h^-1 and yielded polyethylene with a high molecular weight of up to 1 million. In ethylene/1-octene copolymerization, heteroligated metal complexes displayed superior thermal stability again and thus exhibited higher activity than their monoligated and homoligated metal analogues at a high temperature of 120 °C. Moreover, heteroligated metal complexes demonstrated tunable copolymerization capability due to their diverse structures. Therefore, the strategy of designing heteroligated metal catalysts not only enriches the pool of polyolefin catalysts but also endows them with attractive performances, including higher activity, greater thermal stability, and tunable copolymerization properties.