Highly Efficient Catalysts for the Dimerization of α-Olefins

The aim of my work was the catalytic dimerization of a-olefins, especially the dimerization of propylene. The focus was laid on the optimization of product selectivity, catalyst lifetime, and product separation. Previous studies in our group have shown the enormous potential of bis(imino)pyridin vanadium(III) complexes as catalysts for the oligomerization and dimerization of ethylene after activation with MAO. A series of new and literature known complexes was synthesized and tested for the homogeneous catalytic dimerization of propylene after activation with MAO. High selectivities towards dimeric products and within the hexene isomers were observed. The evaluation of the dimerization reactions showed a remarkable influence of the substitution pattern at the ligand framework on the product distribution. Steric demanding substituents at the ortho positions of the iminophenyl ring had positive effects on the dimer yield. The influence of triphenylphosphine as an additive was investigated and strong dependencies could be observed. Addition of triphenylphosphine had no effect on the dimer / oligomers ratio but resulted in the formation of mainly 4-methyl-1-pentene instead of 2-methyl-1-pentene (without additive). Because of the moderate activities of 95–215 10e3 g(dimer)/mol h of the vanadium catalysts, the optimization of the catalytic activity was studied with a phosphine chelated nickel system in the presence of EtAlCl2. Very high activities of up to 52•10e6 g(dimer)/mol•h were observed with an activation ratio of 1:1000 (Ni:Al). These results are comparable to the most active literature known systems. Applying this activation ratio, catalyst life time experiments were performed. Even after seven repetitions of the dimerization experiments, the catalysts showed high activities of up to 87 % of the starting activity. Higher activation ratios resulted in higher selectivities of dimeric products (94 %) but lower activities. After the heterogenization of the catalysts, the amounts of dimeric products were constantly 100%. Under homogeneous and heterogeneous reaction conditions, the same product distributions within the dimer fractions were observed. The use of a fixed bed reactor changed the contact times of the reactants and the catalyst and consequently prevented the formation of higher oligomers and determined the product selectivities. The facile product separation of a heterogeneous system is a great advantage in contrast to the homogeneous system. The simplification of the product separation was the idea for the design of a series of catalysts for the dimerization of propylene. Nickel complexes with phenoxyimine or bisimine ligands were substituted with functional groups for a subsequent covalent linkage with a core shell support material. This silica functionalized magnetic iron core can be separated from the reaction solution by a strong magnetic field. The nickel complexes showed comparable high selectivities and activities for the dimerization of propylene after activation with MAO both under “free” and supported conditions in a closed system. Under both settings, the same products were formed. The described complexes can be used in open or closed systems and offer a high potential for a number of applications. The last chapter of this thesis deals with a very selective system for the dimerization of α-olefins C3-C6 and cis-butene. The special shape of the ligand allows various coordination states for the central metal. The early and late transition metals titanium, cobalt and nickel were combined in different ratios with the potential ligand and tested in dimerization reactions after activation with MAO. While nickel complexes provided the highest activities for the short chain olefins propylene and 1-butene, titanium complexes were more active for the higher olefins 1-pentene and 1-hexene. A change of the activation ratio from 1:500 to 1:1000 raised the activities in all cases. Nickel containing complexes showed high selectivities of even 100% for dimeric products. Titanium and cobalt complexes were selective as well, but did not reach the values of the nickel system.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2010

Author dc:creator

• Lang, Julian

Contributors dc:contributor

• Alt, Helmut

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/363/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:363