Synthesis of Bridged and Unbridged Group (lV) Metallocene Complexes as Catalyst Precursors for Ethylene Polymerization

The aim of this project was the synthesis and characterization of novel bridged and unbridged bis(indenyl) complexes of group IV metals including a study of their catalytic performance in the homogeneous polymerization of ethylene. To accomplish this goal, various ligand precursors were prepared which include 1- and 2-substituted silylindenyl compounds, 1,2-bis(inden-1-yldimethylsilyl)benzene, 2,2’-bis(inden-1-ylmethyl)-1,1’-biphenyl and 9-substituted silylfluorenes. The corresponding dichloride complexes of group IV metals were synthesized and used as catalyst precursors in ethylene polymerization reactions. The first part of this work deals with the synthesis of symmetrical unbridged complexes of zirconium and hafnium derived from 1- and 2-substituted silylindenes and the investigation of their potential in ethylene polymerization reactions. The 1-substituted silyindenyl compounds were obtained by the reactions of chlorosilanes and indenyllithium. The 2-substituted silylindenyl ligand precursors were obtained by a Grignard coupling reaction of aryldimethylchlorosilanes and 2-bromoindene. The corresponding dichloride complexes were synthesized by deprotonation of the substituted indenyl compounds with n-butyllithium and subsequent reactions with zirconium or hafnium tetrachloride in diethyl ether. Applying MAO as a co-catalyst, the synthesized complexes were used in the polymerization of ethylene and the dependence of the activity on the substitution pattern was studied. Among the 1-substituted metallocene catalysts 13-18, catalyst 17 bearing a fluoro atom at the para position of the silyl phenyl group showed the highest activity (4470 kg PE/mol cat. h) while catalyst 16 bearing a methoxy group at the same position was the least active (50 kg PE/mol cat. h). A similar trend was observed for the 2-substituted catalysts (19-24). In general, the 1-substituted catalysts were much more active than the 2-substituted counterparts. The obtained polymers were analyzed by differential scanning calorimetry (DSC) and viscosimetry. The second part describes the synthesis and characterization of a new class of ansa bis(indenyl) complexes of zirconium and hafnium in which the two indenyl moieties are linked at the 1-,1’-positions via a 1,2-bis(dimethylsilyl)-benzene unit. The ligand precursor was prepared via three reaction steps including Grignard coupling of chlorodimethylsilane and 1,2-dibromobenzene, PdCl2-catalyzed chlorination, and the reaction with indenyllithium. The corresponding zirconium and hafnium complexes were obtained by deprotonation of the corresponding bis-(indenyl) compound with n-BuLi followed by metalation reactions of MCl4 (M = Zr, Hf) in THF. The solid state molecular structures of both complexes were established by single crystal X-ray diffraction analyses. In ethylene polymerization reactions, both complexes exhibited high activities. The zirconocene catalyst 34 showed a higher activity (7610 kg PE/mol cat. h) compared to the hafnium catalyst 35 (3590 kg PE/mol cat. h). A second type of ansa-metallocene complexes was synthesized and tested in the homogeneous polymerization of ethylene. The ligand system comprises two indenyl moieties tethered at 3,3’-positions via a 2,2’-dimethyl biphenyl bridge. The ligand precursor was obtained by the reduction of diphenic acid using lithium aluminum hydride (LiAlH4), the reaction with phosphorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by reactions of the corresponding metal tetrachloride. The series of the unsubstituted ansa-complexes (R = H) showed higher activities compared to the methyl substituted counterparts. The zirconium complex 42 showed the highest activity (12460 kg PE/mol cat. h) followed by the hafnium complex 43 (3820 kg PE/mol cat. h) while the titanium complex 40 was inactive which could be attributed to thermal instability and a tendency to decomposition. The introduction of methyl groups at the 1-position of the indenyl moieties leads to a remarkable decrease in the activity probably due to steric hindrance resulting from the two methyl groups. The obtained polyethylenes were analyzed by differential scanning calorimetry (DSC) and viscosimetry. A series of symmetric unbridged 9-substituted dimethyl(tolyl)silyl-fluorenyl complexes of zirconium and hafnium was synthesized, characterized and tested in catalytic ethylene polymerization reactions. These complexes were inactive in the MAO assisted polymerization of ethylene. This could be referred to their instability towards ring-slippage reactions changing the hapticity (η5→ η3→ η1) of the fluorenyl rings.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2011

Author dc:creator

• Abdelbagi, Mohamed Elnaiem Mohamed

Contributors dc:contributor

• Alt, Helmut G.

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/271/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:271