Synthese und Untersuchung pentadentater Liganden und ihrer Lanthanoid(III)-Komplexe

Coordination compounds of lanthanide(III)salts show interesting properties and are used e.g. as lewis acid catalysts in organic synthesis. The precise knowledge about interactions between ligand and Ln(III)-cation as well as the investigation of new ligand systems with low coordination numbers is of particular importance for the application of a complex compound as catalytic system that meets the requirements of efficient catalysis. With regard to these challenges pentadentate, planar ligands were synthesised and used in coordination studies with lanthanide(III) salts. The ligands are based on pyridine with hydrazone- and imine residues in 2,6-position. By introduction of alkyl, aromatic and chiral residues at the hydrazone/ imine functions the ligand system was modified. With the integration of S-containing functions a further modification of the system was achieved. The coordination studies aimed at the formation of 1:1-ligand/metallion-complexes, where the coordination sphere is dominated by the five donor atoms of the ligand. The remaining free coordination sites are filled up by counter anions or solvent molecules. During a catalytic reaction this weak bound molecules can be displaced by substrates, which are possibly activated by coordination to the metal centre. The coordination studies were performed in a stoichiometry of one equivalent metal salt to one equivalent ligand. The small Lu(III)-cation exclusively formed 1:1-complexes. With the bigger La(III)-cation the formation of 1:1- as well as 2:1-ligand/metal ion-complexes was observed. Because of the size of La(III) the coordination of two ligand molecules to the metal centre is sterically enabled but was observed only for some ligands. Until now we can not say which properties of the ligands lead to the exclusive formation of the 1:1 species. We obtained chiral ligands by the introduction of chiral residues as mandelic acid or different amino acids. The absolute configuration of some selected lanthanide(III) complexes was determined by UV- and CD-spectroscopy. We could show the existence of (S,S)-enantiomeres. One X-ray structure of particular interest for this thesis was obtained. It is a 1:1-complex with La(III), whose coordination sphere is filled up with one counter anion and four water molecules. The complex has a charge of two plus, which leads to increased lewis acidity. Furthermore it has free coordination sites available. Therefore the optimal preconditions for an active catalytic system were given and the complex was tested in a first catalytic reaction. This was a Diels-Alder reaction between an oxazolidinone-derivative and cyclopentadiene. The Diels-Alder reaction did not take place. Nevertheless a catalytic reaction was observed. The result was an unexpected hydrolysis of the oxazolidinone that coordinates to the metal centre. So the catalytic cleavage of an amide bond of one of the educts was observed during the test reaction. Now an adequate reaction for further research has to be found. In this thesis a new approach to a ligand family was opened up and the easy, versatile modification of the system was demonstrated. Beside the synthesis of chiral complexes a promising cationc 1:1-complex was obtained and its catalytic activity already could be shown. The application in an adequate reaction and catalytic trials with chiral systems open new challenges