Olefin Polymerization Reactivity of Group 4 Post-Metallocene Catalysts Bearing a Four-Membered C(sp³)-Donor Chelate Ring

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • Cham-Chuen Liu
  • Po-Kam Lo
  • Shek-Man Yiu

Related Research Unit(s)

Detail(s)

Original languageEnglish
Pages (from-to)628-635
Journal / PublicationChemCatChem
Volume11
Issue number1
Online published3 Dec 2018
Publication statusPublished - 9 Jan 2019

Abstract

The synthesis, spectroscopic and structural characterization, and olefin polymerization behavior of a family of pyridine‐2‐phenolate‐6‐arylmethine [O,N,CH(Ar)] Group 4 catalysts bearing a four‐membered N,C(sp3)‐donor metallacycle are described. The racemic [O,N,CH(Ar)] complexes adopt C1 symmetry, as confirmed by NMR spectroscopy and X‐ray crystallography. Advanced NMR experiments have been conducted to probe for possible C−H⋅⋅⋅F−C interactions within fluorinated derivatives. Use of a bis‐pyridyl ligand (Ar=py) resulted in the formation of C2v‐symmetric [O,NCHN] complexes containing a six‐membered partially delocalized N,N‐donor chelate. All complexes have been evaluated as ethylene polymerization catalysts. Notably, the Ti derivatives in conjunction with [Ph3C][B(C6F5)4]/iBu3Al display excellent catalytic efficiencies (TOF over 4×105 h−1 [atm C2H4]−1) at 22 °C, and are considerably more active than previously reported Ti−[O,N,C(σ‐aryl)] relatives. DFT calculations have been performed to gain insights into catalytic behavior. These studies indicate that although the ethylene assimilation process (comprising initial ethylene insertion into the Ti−C(methine) bond of the four‐membered chelate) is accessible, there exists a kinetic preference for normal chain propagation for some catalysts. The DFT results for the Ti−[O,N,CH(Ar)] (Ar=Ph) catalyst are consistent with the narrow molecular weight distributions of the polymers produced (Mw/Mn down to 2.2), suggesting close to single‐site character.

Research Area(s)

  • C ligands, homogeneous catalysis, metallacycles, post-metallocenes, titanium

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