engleski

Rh(I) catalyzed enantioselective hydrogenation using chiral monodentate pseudo-peptide ligands

After the discovery of Wilkinson's homogenous hydrogenation catalyst [RhCl(PPh3)3], chiral phosphine ligands have been used in catalytic enantioselective hydrogenation, with particular emphasis on industrial pplications. Chelating bisphosphorous ligands generally show greater enantioselectivities if compared to monodentate ligands, but moderate to excelent enantioselectivities in catalytic hydrogenation can be achieved with monodentate phosphorous ligands as well. The advantages of monodentate ligands are easier synthesis and straightforward structural variations (ligand library), for finetuning the catalytic properties. Herein, enantionselective catalytic hydrogenation of the model substrate 2-acetamidoacrylate methyl ester is performed by the in situ formed Rh(I) complexes of monodentate triphenylphosphine derived ligands (L) with RhL2 stoichiometry. The ligands, monosubstituted with amino acid chains differing in lenght and peptide sequence (up to three amino acids), were obtained by coupling p-(diphenylphosphine)benzioc acid with the corresponding amino acid or peptide and fully characterized by spectroscopic methods. The catalysis results indicate positive correlation between enantioselectivity and the amino acid chain lenght.

monodentate ligands; supramolecular chemistry; asymmetric catalysis

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