Synthese von immobilisierten Übergangsmetall-Salen-Komplexen, deren Charakterisierung und Einsatz in der enantioselektiven Epoxidierung von 1,2-Dihydronaphthalin

Synthesis of immobilized transitionmetal-salen-complexes, their characterization and use in enatioselective epoxidation of 1,2-dihydronaphthalene by Dipl.-Chem. Eugen Möllmann born in Sindi/Estonia Several transitionmetal-salen-complexes were immobilized in mesoporous materials. These were synthesized starting from commercially available X-, Y- and DAY-zeolites by combining different dealumination methods. As a result the created mesopores are completely surrounded by micropores. During the dealumination process the zeolites were analyzed by 27Al- and 29Si-MAS-NMR methods. The starting as well as the final material were additionally characterized by N2 adsorption. For a complete characterization of the geometry of the created mesopores two independent MAS-NMR methods were applied. Mean pore diameters were obtained by measuring the chemical shift of adsorbed 129Xe. A poresize distribution was calculated from measurements of the freezing point depression of water that is occluded inside the pores. The modified zeolites were used as carrier materials for chiral transitionmetal-salen-complexes. The synthesis of the complexes inside the mesopores (ship in a bottle principle) was done taking the template synthesis approach. The final catalysts were characterized by elemental analysis, UV-Vis and IR spectroscopy and then applied in the enantioselective epoxidation of 1,2-dihydronaphthalene. Screening of several oxygen donor systems revealed that molecular oxygen in combination with sacrificial aldehydes didn't result in a transfer of chiral information. H2O2 in combination with ammonium acetate results in average enantiomeric excesses and low conversions due to a destruction of the catalyst. Experiments with basic NaOCl-solutions showed significantly better enantiomeric excess and conversions on one hand, on the other hand the carrier material was dissolved by the basic aqueous system. As a result a recyclization was like in the previous systems not possible. Switching to a suspension of Ca(OCl)2 in acetone left the zeolite structure unharmed so that a recyclization became possible. In a recycled run selectivities and enantiomeric excesses were lower while conversions stayed at the same level. To investigate the dynamics of an immobilized salen complex, molecular dynamics calculations were done. The simulation temperatures were varied between 240 and 310 K for an unsubstituted Co-salen-complex inside and outside of a zeolite matrix. From mechanisms for the enantioselective epoxidation with salen catalysts discussed in literature the observables were derived. As a result the occluded complex is more distorted than the free complex and therefore is more likely to block a path for the approach of the substrate. Furthermore due to the immobilization the complex is more confined to a given conformation. This is a hint for the ability of the zeolite to stabilize conformations at higher temperature.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Möllmann, Eugen

Contributors dc:contributor

• Hölderich, Wolfgang F.

• info:eu-repo/classification/ddc/540
• Flaschenschiffkatalysator
• Übergangsmetallkomplexe
• Salen
• Wirtsmolekül
• Zeolith
• Mesoporöser Kristall
• Dihydronaphtaline
• Epoxidation
• Asymmetrische
• Chemie
• Immobilisierung
• ship in a bottle
• enantioselektive Katalyse
• Salen Komplexe
• Molecular Modelling

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121023%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59217