Analyses of Propene and 1-Hexene Oligomers from Zirconocene/MAO Catalysts - Mechanistic Implications by NMR, SEC, and MALDI-TOF MS

Abstract

A series of Cp′(C5H5)ZrCl2 and Cp′2ZrCl2 pre-catalysts (Cp′ = C5HMe4, C4Me4P, C5Me5, C5H4tBu, C5H3-1,3-tBu2, C5H2-1,2,4-tBu3) together with (C5H5)2ZrCl2 was used for the directed oligomerization of propene and 1-hexene in comparative experiments. Oligomer characterization was carried out by 1H NMR, SEC (GPC), MALDI-TOF MS, cryoscopy and Raman spectroscopy. From 1H NMR the nature and relative ratio of the double-bond end group is determined together with M̄n if every oligomer molecule contains such a double-bond end group. Normally vinylidene double bonds (from β-hydrogen elimination) are found. From 1H NMR and MALDI-TOF MS also vinyl end groups (from β-methyl elimination) are observed in the case of oligopropenes with (C4Me4P)- (C5H5)ZrCl2 and with the symmetrical methyl containing Cp′2ZrCl2 pre-catalysts. The vinylidene/vinyl ratio depends on the ligand and increases from C5HMe4 (65/35) over C4Me4P (61/39) to C5Me5 (9/91). A comparison of M̄n from 1H NMR and SEC together with MALDI-TOF MS shows that the phospholyl-zirconocenes and (C5HMe4)2ZrCl2 also exhibit chain transfer to aluminium, thereby giving saturated oligomers.