Synthesis and characterisation of permethylindenyl zirconium complexes and their use in ethylene polymerisation

Abstract

We report the synthesis of two zirconocenes, dimethylsilylbis(hexamethylindenyl) zirconium dichloride, rac-(SBI*)ZrCl_2, and ⁿbutyldimethylsilyl(hexamethylindenyl) zirconium trichloride, [(Ind*SiMe₂ⁿBu)Zr(μ-Cl)Cl₂]₂. The complexes were characterised by NMR spectroscopy and X-ray crystallography, and the bonding was evaluated using density functional theory. rac-(SBI*)ZrCl₂ demonstrated a very high activity for solution phase polymerisation of ethylene (ca. 22 500 kg_PE⁻¹ mol_Zr⁻¹ h⁻¹ bar⁻¹). Both rac-(SBI*)ZrCl₂ and rac-(EBI*)ZrCl₂ (EBI* = ethylenebis(hexamethylindenyl)) have been supported on MAO modified silica and AMOST layered double hydroxides (AMO-LDHs), and evaluated as catalysts in the slurry-phase polymerisation of ethylene. The highest catalytic polymerisation activities for rac-(SBI*)ZrCl₂ and rac-(EBI*)ZrCl₂ on the layered double hydroxides were 9657 and 4325 kg_PE⁻¹ mol_Zr⁻¹ h⁻¹ bar⁻¹ respectively, for MAO modified Mg₂Al–SO₄ LDH. However, rac-(EBI*)ZrCl₂ was a three times more active catalyst than rac-(SBI*)ZrCl₂ when supported on silica.