Synthesis of Group (lV) Transition Metal Complexes and their Applications as Catalysts for Ethylene Polymerization

The aim of the project included the synthesis and characterization of new group (IV) metal complexes and their applications as catalysts in homogeneous ethylene polymerization reactions. For this purpose, different types of organic compounds and their group (IV) metal complexes were synthesized and tested for ethylene polymerization after activation with MAO. The first part of this work describes the synthesis of symmetric and asymmetric metallocene dichloride complexes bearing bulky alkoxy substituents on indenyl moieties and the investigation of their potential as ethylene polymerization catalysts. Indenyl compounds bearing bulky alkoxy substituents can be prepared by refluxing phenol or naphthol derivatives with w-bromo-1-indenylalkanes and potassium carbonate in the presence of catalytic amounts of 18-crown-6 in acetone. They can be prepared in better yields by the reaction of w-bromo-1-phenoxyalkanes with indenyl lithium. Symmetric metallocene dichloride complexes were synthesized by deprotonating the alkoxy substituted indenyl compounds with n-butyllithium followed by the reaction with metal tetrachlorides. Asymmetric metallocene dichloride complexes were synthesized by deprotonating alkoxy substituted indenyl compounds with n-butyllithium followed by the reaction with indenyl zirconium trichloride. The second part of this work deals with the synthesis of bis (indenyl) zirconium dichloride complexes bearing bulky 9-methyl fluorenyl substituents. 9-Methyl fluorenyl substituted indenyl compounds can be synthesized by the reaction of w-bromo-1-indenylalkanes with the lithium salt of 9-methyl fluorene. The reaction of zirconium tetrachloride with the lithium salts of the substituted indenyl compounds afford the bis (indenyl) zirconium dichloride complexes in good yields. Asymmetric chelating diamide complexes of titanium and zirconium were also synthesized and tested for ethylene polymerization as a part of the project. Reaction of the desired aniline with an appropriate dibromoalkane compound affords the N-substituted bromoalkyl aniline derivative which can react with tertiary butyl amine to yield the desired asymmetric diamine compound. Deprotonation of the diamine compounds with n-butyllithium followed by the reaction with titanium tetrachloride or zirconium tetrachloride yields the desired chelating diamide complexes. Titanium and zirconium complexes with a Schiff base derivative of 2-(2-aminophenyl)benzothiazole were also synthesized. The reaction of 2-(2-aminophenyl)benzothiazole with benzaldehyde yields its Schiff base derivative which can react with titanium tetrachloride or zirconium tetrachloride to afford the desired complexes. The above mentioned complexes were used for homogeneous ethylene polymerization after activation with MAO (M:Al = 1:2000). The alkoxy substituted metallocene catalysts showed good to moderate activities which depend on the length of the bridging alkylidene chain between alkoxy group and indenyl ligand of the zirconocene dichloride complex as well as the steric bulk of the alkoxy substituent. The activity maximum (27467 kg PE/mol cat. h) was found for a chain length of four carbon atoms. Further increase or decrease in the chain length resulted in a decrease of activity. The decrease of steric bulk at the phenoxy group also resulted in a decrease of activity. The 9-methyl fluorenyl substituted metallocene catalysts showed good activities towards ethylene polymerization. The catalyst with butylidene bridge between 9-methyl fluorenyl group and indenyl ligand showed the maximum activity (15786 kg PE/mol cat. h). The activated asymmetric chelating diamide complexes of titanium and zirconium (M:Al = 1:1000) showed low activities. The complex bearing bulky isopropyl groups at the aniline moiety showed the highest activity (263 kg PE/mol cat. h). The activity decreased by decreasing the steric bulk at the aniline moiety. Titanium and zirconium complexes of the Schiff base derivative of 2-(2-aminophenyl) benzothiazole also showed low activities (432 and 276 kg PE/mol cat. h) after activation with MAO (M:Al = 1:2000). A possible reason for the low activity could be the coordination of the sulphur atom to the active species. The symmetric alkoxy substituted metallocene catalysts produced polyethylenes of lower melting points, melting enthalpies, crystallinities and viscosity average molecular weights (112.9 J/mol, 126 °C, 0.39 and 270000 g/mol than their asymmetric analogues (155.3 J/mol, 137.2 °C, 0.54 and 420000 g/mol). The polyethylenes produced by 9-methyl fluorenyl substituted metallocene catalysts are of medium melting points, melting enthalpies and crystallinities (142 J/mol, 129.3 °C and 0.49). The polyethylenes produced by the asymmetric chelating diamide catalysts have medium melting points but low melting enthalpies and crystallinities (137.8 J/mol, 116.5 °C and 0.44).

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2010

Author dc:creator

• Ahmad, Khalil

Contributors dc:contributor

• Alt, Prof. Dr. Helmut G.

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/362/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:362