Novel zirconium complexes with constrained cyclic β-enaminoketonato ligands: improved catalytic capability toward ethylene polymerization
writer：Kai-Ti Wang, Yong-Xia Wang, Bin Wang, Yan-Guo Li*， Yue-Sheng Li*
keywords：Zr(IV) and Hf(IV) complexes，constrained cyclic β-enaminoketonato， ethylene polymerization
source：期刊
Issue time：2016年
Novel Zr(IV) and Hf(IV) complexes bearing two constrained bulky β-enaminoketonato ligands {[ArNvCH– C8H3(CH2)n(R)O]2MBn2, M = Zr or Hf; n = 1, 2 or 3; R = H or C6H5; Ar = C6H5 or C6F5} were synthesized and clearly characterized. X-ray crystal structure analysis reveals that these complexes adopt a distorted octahedral geometry. Compared with non-constrained analogues, the Zr(IV) complexes with a cyclic skeleton exhibited high catalytic activities (up to 16.4 kgPE mmolZr?1 h?1) toward ethylene polymerization at ambient pressure and elevated temperatures. Moreover, the catalytic properties of these complexes could be governed exquisitely by appropriate variation of the N-aryl substituents and the size of the benzocyclane. The Zr(IV) complexes bearing a non-flfluorinated N-aryl group yielded oligomers, while the flfluorinated analogues bearing a fifive-membered or six-membered cyclane group produced high molecular weight polyethylenes (33.4–306 kg mol?1) under similar conditions on account of the suppression effffects on β-H elimination. The Zr(IV) complexes are more active toward ethylene polymerization than the Hf(IV) analogues, and the resulting polymers exhibited higher molecular weight and narrower molecular weight distribution.