title: Novel zirconium complexes with constrained cyclic β-enaminoketonato ligands: improved catalytic capability toward ethylene polymerization.
abstract: Novel Zr(iv) and Hf(iv) complexes bearing two constrained bulky β-enaminoketonato ligands {[ArN[double bond, length as m-dash]CH-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-fluorinated N-aryl group yielded oligomers, while the fluorinated analogues bearing a five-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 effects 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.
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China. liyg@ciac.jl.cn and University of Chinese Academy of Sciences, Changchun Branch, Changchun 130022, China.
authors.forename: Kai-Ti
authors.initials: KT
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China. liyg@ciac.jl.cn.
authors.forename: Yong-Xia
authors.initials: YX
authors.lastname: Wang
authors.affiliation: Tianjin Key Lab Composite & Functional Materials, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China. ysli@tju.edu.cn.
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China. liyg@ciac.jl.cn.
authors.forename: Yan-Guo
authors.initials: YG
authors.lastname: Li
authors.affiliation: Tianjin Key Lab Composite & Functional Materials, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China. ysli@tju.edu.cn and University of Chinese Academy of Sciences, Changchun Branch, Changchun 130022, China.
authors.forename: Yue-Sheng
authors.initials: YS
authors.lastname: Li