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Heteroligated Hafnium Complexes with Enhanced Activity and Thermal Stability toward Olefin (Co)polymerization
Yongxin Liu1, Faqiang Niu1, Shaofeng Liu1,2
1Shandong Key Laboratory of High Performance Polyolefin Materials and Recycling, College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao, Shandong 266042, China.
None:
Three heteroligated Hf metal complexes, [C5H4N-CH(Me)-N-2,6-R1-C6H3][C6H5-N-C6H4-S-R2]HfMe2 (for Hf1/3, R1 = iPr and R2 = Me; for Hf2/3, R1 = Me and R2 = Me; for Hf2/4, 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 Hf1, R1 = iPr; for Hf2, R1 = Me) and thioether-amido ligands C6H5-N-C6H4-S-R2 (for L3, R2 = Me; for L4, R2 = Ph) and employed for olefin (co)polymerization. For comparison, homoligated metal analogue [C6H5-N-C6H4-S-Me]2HfMe2 (Hf3/3) was also prepared. In ethylene homopolymerization, heteroligated metal complexes (Hf1/3, Hf2/3, and Hf2/4) exhibited higher activity and better thermal stability than monoligated and homoligated metal analogues (Hf1, Hf2, and Hf3/3). In particular, Hf1/3 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.
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