hide
Free keywords:
-
Abstract:
N-heterocyclic carbene (NHC) ligands have become universal ligands in organometallic and inorganic coordination chemistry and their application in homogeneous transition metal complex catalysis has already become state of the art. Beside scientific progress towards readily available NHC ligands synthesis of new and even more efficient NHC ligands is of main interest, either in organometallic catalysis or as organocatalysts themselves. Up to now asymmetric catalysis with NHC ligands represents one of the most challenging fields herein and only some examples of NHC based asymmetric inductions are reported.
The first part of the present master thesis is based on the synthesis of the, in terms of C-C/C-N-rotation, complete rigid N-heterocyclic carbene ligand 1 containing chirality, which is introduced through a pair of camphor building blocks. The synthesis of the N-heterocyclic carbene ligand 1 was accomplished in 11 steps.
The key step in synthesis was the intramolecular, twofold ring-closure reaction to bis((7,7-dimethyl-norbornane)-1,3-oxazine) (12) in step 10. For this purpose various methods and two test-compounds possessing related structural architectures were investigated.
Care was especially taken on the separation as well as on characterization of the corresponding diastereomers (exo, exo-, endo, exo-11 – 13 and endo, endo-11) formed during synthesis. Furthermore, new routes in order to shorten the total synthesis of the target imidazolium salt 1 were conceived and investigated.
In the second part, synthesis and immobilization of the symmetric NHC ligand 23 onto a hydridodimethylpolysiloxane support is described and experiments towards transition-metal complex formation were conducted. Immobilization and formation of active transition-metal complexes on such a support is expected to show improved performance combining the advantages of homogeneous and heterogeneous catalysis.
