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Synthesis and characterization of chiral monodentate pseudo-peptide ligands and supramolecular asymmetric catalysis with their metal complexes

In recent years, supramolecular catalysis has overlapped with many areas of synthetic, material and biological chemistry.[1, 2] It has been postulated that a supramolecular catalyst should contain a functional group for the catalysis and a motif for the assembly process via non-covalent interactions, i.e. π–π stacking, hydrogen bonding, electrostatic or van der Waals interactions. Supramolecular catalysis is particularly attractive because it often uses only simple monodentate ligands, easily accessible in a few synthetic steps. In the present work, chiral monodentate pseudo-peptide ligands L1 – L10 were prepared. The phosphorus donor atoms in L1 – L10 can bind transition metals like Rh(I), Pt(II) or Pd(II) with a 2 : 1 ligand to metal stoichiometry. In the resulting supramolecular L2M complexes, the pedant amino acids can form inter-strand hydrogen bonds, while the central aromatic unit can exhibit π – π stacking. Longer and/or branched amino acid chains in L6 – 10 allow the formation of more inter-strand hydrogen bonds and therefore stronger supramolecular interactions. The prepared metal complexes were characterized by various spectroscopic techniques and tested as catalysts in model asymmetric reactions.

monodentate ligands; supramolecular chemistry; asymmetric catalysis

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