Publikationsserver der RWTH Aachen University
Funktionalisierte hierarchisch gebildete Helicate
Abstract
dc:descriptionThe work bases on synthesis and study of helicates formed by hierarchical self-assembly. Self-assembly plays an important role in nature as well as in many chemical processes. Small building blocks assemble to supramolecules. For molecular recognition, perfect design of the sub-units is essential to generate one defined species. A variety of catechol-ligands bearing a carbonyl function in three position were synthesised. These ligands, titanium(IV) and lithium form in a hierarchical self-assembly dinuclear triple stranded helicates. The first recognition step generates a mononuclear complex of three ligands and one metal ion. In a second recognition process two mononuclear complexes connect by three lithium ions to a helicate. Due to statistics a racemic mixture of P- and M- helicate is formed. The helicate has a stable configuration, while the mononuclear complex undergoes fast racemization and configuration change. An equilibrium between both complexes exists. A strong carbonyl donor (ester) and a methanol (weak lithium solvation) leads to the helicate as major product, while dimethylsulfoxid (strong lithium solvation) and weak carbonyl donors (aldehyde) shift the equilibrium to the mononuclear species. The system was modified in different positions to study the influence of parts of the complex. Boron(III) as coordination centre leads to dinuclear double stranded helicates, which show blue to green fluorescence. Also the organic ligands were modified by introducing new units to generate functional helicates. A ligand with two hexylester-units at the catechol core was synthesised. Mixing this ligand with titanium(IV) and lithium leads to oligomeric complexes. Replacing lithium by potassium switches the system to the monomer as single product. Another ligand bearing a thiomorpholin unit was made to generate monolayers on gold surfaces. Studies are still in process. To understand solvent influence on hierarchical self-assembly, two different types of ligands were synthesised by modifying the ester function in three position of the catechol. One type bears long alkyl chains to make the complex soluble in non-polar solvents like chloroform or benzene. The other extreme is water as solvent. For complexation studies in water, a ligand with a carboxylic unit was prepared. Titanium complexes with both ligands were studied by NMR- techniques and ESI-MS. In non-polar solvents the helicate is the only product due to weak lithium solvation. In water, an equilibrium of monomer and dimer is detected due to strong lithium solvation by solvent molecules. Another approach was to produce dendrimers in one step by supramolecular assembly. Ligands bearing a Frechet-unit (zero to third generation) were synthesised, they form with titanium(IV) and lithium dense dendrimers consisting of six ligands and two metal ions. Helical twist of these complexes was proven by solid state structure. The last part of the thesis deals with diastereoslective influence of enantiomerical pure ligands on helicate formation. Titanium complexes with different enantiomerical pure ligands were synthesised. These helicates were analysed by NMR- and CD-techniques. NMR measurements showed more or less diastereoselective induction depending on the distance of the chiral centre to the coordination unit. Chiral information was transferred from ligand to supramolecule and selective formation of one enantiomer was achieved. CD-measurement in methanol as well as in dimethylsulfoxid were carried out. In combination with tddft-calculations the absolute configuration was determined. Switching between monomer and dimer is possible by solvent change. First studies also indicate a different configuration for mononuclear complex and helicate made of the same ligand. Versatility of the concept was proven by investigations in synthesis and study of hierarchical assembled helicates based on 3-carbonyl-catechol-ligands in combination with titanium(IV) and lithium.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2009
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Baumert, Miriam
- Contributors dc:contributor
-
- Albrecht, Markus
Subjects
dc:subject × 9Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger