Mononuclear and Dinuclear Complexes of Allylated alpha-Diimines as Catalysts for the Polymerization of Ethylene

It was the goal of this project to synthesize dinuclear catalysts that provide two different active sites for the oligomerization and polymerization of alpha-olefins, especially ethylene. The plan of synthesis involves precursors consisting of a diimine moiety coordinated to a late or early transition metal and a metallocene or half sandwich moiety. In order to achieve these goals, some alpha-diimine compounds were functionalized with allyl or alkyl halide groups and then coupled with a metallocene or a half sandwich complex. Three different alpha-diimine compounds were synthesized and characterized by GC-MS, 1H NMR, and 13C NMR spectroscopy. These compounds are bearing allyl functions at their backbones and different ortho substituents at the arene moieties of their frameworks. 21 different complexes were prepared using these compounds and they were characterized by mass spectroscopy and elemental analysis. These complexes were activated with methylalumoxane (MAO) and tested for the catalytic polymerization of ethylene. The ethylene polymerization results revealed that the bulkier the substituents at the aryl rings of the catalyst structure, the lower the polymerization activity. These results are compatible with the chain running mechanism which suggests that bulky substituents can hinder the monomers from reaching the active catalytic centers due to their interaction with the axial coordination sites of the metal centers. The palladium catalysts showed no polymerization activity as distinguished behavior. That may attribute to the allyl functions attached to the backbone of the catalyst structures which can interact with the active sites of the palladium catalysts resulting in blocking the active sites and deactivating the catalyst. Five alpha-diimine complexes bearing allyl groups were coupled with a bridged zirconocene complex possessing a hydride silane moiety via hydrosilylation reaction in the presence of Karstedts catalyst to afford five new dinuclear precursors. These dinuclear precursors were activated with methylalumoxane (MAO) and tested for the polymerization of ethylene. The bridged silyl zirconocene moiety is the same for all these dinuclear complexes. Therefore, the ethylene polymerization activities of their catalysts showed a dependence on the variant metal centers of the á-diimine moiety. The trend of polymerization activities was: Ni > Pd > V > Zr > Ti. The produced polyethylenes were analyzed via gel permeation chromatography (GPC). The GPC results showed broad molecular weight distributions due to the dual sites of these catalysts. The GPC spectrum of polyethylene produced with the dinuclear catalyst 13 was discussed as an example and compared with the GPC spectrum of polyethylene produced with its mononuclear catalyst 6f. Six novel dinuclear precursors consisting of alpha-diimine moieties connected to half sandwich metallocene complexes were prepared and characterized via mass spectroscopy and elemental analysis. These dinuclear precursors were activated with methylalumoxane (MAO) and tested for the polymerization of ethylene. The ethylene polymerization activities of these dinuclear catalysts demonstrated a dependence on the size of the ortho substituents at the aryl rings of the catalysts structures. The results of ethylene polymerization agreed with the chain running mechanism: the bulkier the substituents the lower the polymerization activities. The results of gel permeation chromatography (GPC) of polyethylene produced by these catalysts exhibited bimodal molecular weight distributions. These results can be assigned to the different active sites of the dinuclear catalysts. The GPC spectra of polyethylenes produced with the dinuclear catalysts 18a,b were discussed as examples.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2009

Author dc:creator

• Al-Shammari, Haif

Contributors dc:contributor

• Alt, Helmut G.

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/444/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:444