Alkyl-substituted cyclopentadienyl- and phospholyl-zirconium/MAO catalysts for propene and 1-hexene oligomerization

The directed oligomerization of propene and 1-hexene was carried out with a series of Cp′(C5H5)ZrCl2 and Cp2′ZrCl2 pre-catalysts (Cp′=C5HMe4, C4Me4P, C5Me5, C5H4tBu, C5H3-1,3-tBu2, C5H2-1,2,4-tBu3) together with (C5H5)2ZrCl2. Oligomers in the molar mass range 300–1500g/mol for propene and 200–3000g/mol for 1-hexene were synthesized at 50°C. The majority of oligomer molecules contain a double-bond end group. Oligomer characterization was carried out by gel permeation chromatography (GPC), 1H and 13C NMR. Vinylidene double bonds (from β-hydrogen elimination) are solely found for the tert-butyl-substituted zirconocenes and for most of the unsymmetrical methyl-substituted Cp′(C5H5)ZrCl2 systems (except Cp′=phospholyl). With (C4Me4P)(C5H5)ZrCl2 and with the symmetrical methyl-containing Cp2′ZrCl2 pre-catalysts, also vinyl end groups (from β-methyl elimination) are observed in the case of oligopropenes. The vinylidene/vinyl ratio depends on the ligand and the vinyl content increases from C5HMe4 (65/35) over C4Me4P (61/39) to C5Me5 (9/91). The phospholyl zirconocenes and (C5HMe4)2ZrCl2 also exhibit chain-transfer to aluminum thereby giving saturated oligomers.