Novel zirconium complexes with constrained cyclic β-enaminoketonato ligands: improved catalytic capability toward ethylene polymerization. Issue 25 (31st May 2016)

• Record Type: Journal Article
• Authors: Wang, Kai-Ti; Wang, Yong-Xia; Wang, Bin; Li, Yan-Guo; Li, Yue-Sheng
• Is Part Of: Dalton transactions. Volume 45:Issue 25(2016)
• Page Start: 10308
• Page End: 10318
• Publication Date: 2016-05-31
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt01391k
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The synthesized bis(β-enaminoketonato) zirconium complexes bearing a cyclic skeleton exhibited improved capabilities toward ethylene polymerization even at high temperatures. Abstract : Novel Zr(iv ) and Hf(iv ) complexes bearing two constrained bulky β-enaminoketonato ligands {[ArNCH–C8 H3 (CH2 ) n (R)O]2 MBn2, M = Zr or Hf; n = 1, 2 or 3; R = H or C6 H5 ; Ar = C6 H5 or C6 F5 } 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.