Application of the 2-Pyridone Hydrogen-Bonding Motif in Supramolecular Catalysis and in Phenanthroline Based Ligands

Abstract: This thesis concentrates on the development, synthesis and evaluation of supramolecular systems, assembled from its components by means of hydrogen bonding, using the self-complementary 2-pyridone motif. The thesis is divided in two parts. 1) Supramolecular catalysis: Substrate selectivity is imposed on a derivative of Jacobsen's catalyst, an Mn(salen) complex with 2-quinolone hydrogen-bonding groups in the 5,5'-positions, by noncovalently attaching a receptor functionality, a Zn(tetraarylporphyrin) with appending 2-pyridone groups. The hydrogen-bonding functionalities are arranged in a way to favor the formation of a dynamic macrocyclic heterodimer. The resulting catalytic system shows substrate selectivity in the Jacobsen-Katsuki (J-K) epoxidation, favoring pyridine appended styrene derivatives, capable of binding to the receptor, over phenyl appended ones. The substrate- and enantioselectivity of the catalyst as well as its reactivity and stability have been probed at various reaction conditions to obtain an understanding of the mechanisms underlying the substrate selectivity. In the interpretation of the results of the catalysis experiments, novel aspects on the mechanism of J-K epoxidation have emerged. Suggestions on how to improve the substrate selectivity in future generations of the present supramolecular catalytic system have also been derived from these results. 2) Phenanthroline based ligands: Solid state structures of a 2-pyridone fused phenanthroline based (phenamide) ligand and its Cu(I) complex were analyzed. Both revealed unexpected hydrogen bonding behavior of the 2-pyridone moiety. The free ligand crystallized in the highly unusual packing mode P-1 Z = 7, Z' = 3.5. The Cu(I) complex is a potential building block for chiral linear hydrogen-bonded coordination polymers, but the Cu(I) complex of the first generation of phenamide ligand did not produce the anticipated polymer structure in the solid state. The observed structure was a result of competition between hydrogen-bonding and pi-stacking.