Ternary metallocene catalyst systems based on metallocene dichlorides and AlBu 3i/[PhNMe 2H][B(C 6F 5) 4] : NMR investigations of the influence of Al/Zr ratios on alkylation and on formation of the precursor of the active metallocene species

Abstract

The formation of the precursors of the polymerization-active species of the metallocene dichlorides Cp 2ZrCl 2 and Ph 2C(CpFlu)ZrCl 2 by successive reaction with AlBu 3 i and [PhNMe 2H][B(C 6F 5) 4] was investigated by means of NMR spectroscopy. More than two equivalents of AlBu 3 i are required for total conversion of the metallocene dichlorides in the first step. The reaction of Ph 2C(CpFlu)ZrCl 2 with AlBu 3 i leads exclusively to the mono- iso-butyl complex Ph 2C(CpFlu)ZrClBu i, independent of the surplus AlBu 3 i used, whereas in the case of Cp 2ZrCl 2 a series of metallocene products are observed, depending on the Al/Zr ratio used. When this ratio was increased to above 10, the reaction could be exclusively directed to form the dimer metallocene complex [Cp 2ZrH 2·AlBu 3 i] 2. The reaction of [PhNMe 2H][B(C 6F 5) 4] with metallocene/aluminium alkyl mixtures prepared with 10, 20, 50 and 100 equivalents of AlBu 3 i leads to the precipitation of an oily liquid, which contains resulting cationic metallocene complexes. These liquid phases can be purified by extraction and subsequently used for NMR measurements. With one exception, mixtures of two or three different cationic metallocene products are obtained, depending on the Al/Zr ratio and on the metallocene ligand used. An Al/Zr ratio of 100 the reaction of the Ph 2C(CpFlu)ZrCl 2/AlBu 3 i mixture with [PhNMe 2H][B(C 6F 5) 4] exclusively leads to the cationic heterodinuclear metallocene complex [Ph 2C(CpFlu)Zr-μ-H-μ-(C 4H 7)-AlBu 2 i] +, a novel type of allyl-bridged cation, which was characterized by NMR data. None of the reactions of metallocene dichloride/aluminium alkyl mixtures with [PhNMe 2H][B(C 6F 5) 4] lead to the degradation of [B(C 6F 5) 4] −, whereas in the absence of metallocenes AlBu 3 i reacts with [PhNMe 2H][B(C 6F 5) 4] to give AlBu 3− x i(C 6F 5) x compounds. Based on these results and with additional information from the literature a mechanism is proposed to explain the formation of [Ph 2C(CpFlu)Zr-μ-H-μ-(C 4H 7)-AlBu 2 i] +.