Half-sandwich β-diketonato complexes of zirconium and their application as catalysts to ethylene polymerization

Abstract

The bis(β-diketonato) Zr complexes CpZr(acac)2Cl (acac = acetylacetonato) (1) and Cp*Zr(acac)2Cl (2) can be synthesized by the reaction of Cp′ZrCl3(Cp′ = Cp or Cp*) with 2 equiv of lithium acetylacetonate. CpZr(acac)2Cl (1) can be quantitatively prepared by treatment of Cp2ZrCl2 with excess acetylacetone. The tris(β-diketonato) Zr complex CpZr(tfac)3 (tfac = trisfluoroacetylacetonato) (3) has been prepared by treatment of CpZrCl3 with sodium trisfluoroacetylacetonate. The replacement of both chlorine atoms and one Cp group from zirconocene dichloride by nonfluorinated diketone, acetylacetone, readily occurs at room temperature in triethylamine medium, offering the tris(β-diketonato) Zr complex CpZr(acac)3 (4). The complexes were characterized by 1H NMR spectroscopic methods. In addition, the molecular structures of complexes 3 and 4 have been determined by X-ray diffraction methods. When activated by excess methylaluminoxane (MAO), these complexes were active for ethylene polymerization, offering polyethylenes with high molecular weights and narrow molecular weight distributions. Complex 4 showed a very high ethylene polymerization activity of up to 7100 kg PE/mol Zr·h at 5 atm. Complexes 1 and 2 were also active for ethylene/1-hexene copolymerization.