Titanium and zirconium complexes with non-salicylaldimine-type imine-phenoxy chelate ligands: Syntheses, structures, and ethylene- polymerization behavior

Yasuhiko Suzuki, Hidetsugu Tanaka, Toshiyuki Oshiki, Kazuhiko Takai, Terunori Fujita

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

New Ti and Zr complexes that bear imine-phenoxy chelate ligands, [{2,4-di-tBu-6-(RCH = N)C6H4O}2MCl2] (1: M = Ti, R = Ph; 2: M = Ti, R = C6F5; 3: M = Zr, R = Ph; 4: M = Zr, R = C6F5), were synthesized and investigated as precatalysts for ethylene polymerization. 1H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X-ray crystallographic analysis of the adduct 1·HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X-ray molecular structure also indicates that one imine phenoxy group with the syn C=N configuration functions as a bidentate ligand, whereas the other, of the anti C=N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph 3C]+[B(C6F5)4] -/AliBu3 displayed moderate activity, the Ti congeners 1 and 2, in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25°C, 2 displayed a very high activity of 19900 (kg PE)(mol Ti)-1 h-1, which is comparable to that for [Cp2TiCl2] and [Cp 2ZrCl2], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C6F5 group on the imine nitrogen atom and mediated nonliving-type polymerization, unlike the corresponding salicylaldimine-type complex. Conversely, with [Ph3C]+[B(C6F 5)4]-/AliBu3 activation, 1 exhibited enhanced activity as the temperature was increased (25-75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE)(mol Ti)-1 h -1). 1H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine-phenoxy complex as the catalytically active species. The combinations 1/[Ph3C] +[B(C6F5)4]-/AliBu3 and 2/MAO also worked as high-activity catalysts for the copolymerization of ethylene and propylene.

Original languageEnglish
Pages (from-to)878-887
Number of pages10
JournalChemistry - An Asian Journal
Volume1
Issue number6
DOIs
Publication statusPublished - 2006

Fingerprint

Imines
Titanium
Polymerization
Ligands
Nitrogen
Chemical activation
X-Rays
X rays
Atoms
Temperature
Molecular Structure
Isomers
Copolymerization
Molecular structure
Nuclear magnetic resonance spectroscopy
Amines
Catalyst activity
Magnetic Resonance Spectroscopy
Thermodynamic properties
Metals

Keywords

  • Catalysts
  • Complexes
  • Polymerization
  • Titanium
  • Zirconium

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Titanium and zirconium complexes with non-salicylaldimine-type imine-phenoxy chelate ligands : Syntheses, structures, and ethylene- polymerization behavior. / Suzuki, Yasuhiko; Tanaka, Hidetsugu; Oshiki, Toshiyuki; Takai, Kazuhiko; Fujita, Terunori.

In: Chemistry - An Asian Journal, Vol. 1, No. 6, 2006, p. 878-887.

Research output: Contribution to journalArticle

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N2 - New Ti and Zr complexes that bear imine-phenoxy chelate ligands, [{2,4-di-tBu-6-(RCH = N)C6H4O}2MCl2] (1: M = Ti, R = Ph; 2: M = Ti, R = C6F5; 3: M = Zr, R = Ph; 4: M = Zr, R = C6F5), were synthesized and investigated as precatalysts for ethylene polymerization. 1H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X-ray crystallographic analysis of the adduct 1·HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X-ray molecular structure also indicates that one imine phenoxy group with the syn C=N configuration functions as a bidentate ligand, whereas the other, of the anti C=N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph 3C]+[B(C6F5)4] -/AliBu3 displayed moderate activity, the Ti congeners 1 and 2, in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25°C, 2 displayed a very high activity of 19900 (kg PE)(mol Ti)-1 h-1, which is comparable to that for [Cp2TiCl2] and [Cp 2ZrCl2], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C6F5 group on the imine nitrogen atom and mediated nonliving-type polymerization, unlike the corresponding salicylaldimine-type complex. Conversely, with [Ph3C]+[B(C6F 5)4]-/AliBu3 activation, 1 exhibited enhanced activity as the temperature was increased (25-75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE)(mol Ti)-1 h -1). 1H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine-phenoxy complex as the catalytically active species. The combinations 1/[Ph3C] +[B(C6F5)4]-/AliBu3 and 2/MAO also worked as high-activity catalysts for the copolymerization of ethylene and propylene.

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KW - Polymerization

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KW - Zirconium

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