Metallkomplexe mit biologisch wichtigen Liganden, CXXXVII [1]. Halbsandwich-Komplexe mit N, O-Chelaten und Schiff-Basen von β-Aminosäuren/ Metal Complexes of Biologically Important Ligands, CXXXVII [1]. Halfsandwich Complexes with N, O-Chelates and Schiff Bases of β-Amino Acids

Koch, Daniela; Hoffmüller, Winfried; Polborn, Kurt; Beck, Wolfgang

doi:10.1515/znb-2001-4-513

Cited by 14 publications

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“…Transition metal complexes with chiral N^O-chelate Schiff base ligands are of continued interest − and have been used efficiently as chiral catalysts. , We have recently paid attention to the syntheses, characterization, diastereoselectivity, and molecular structures of four-coordinated nonplanar chiral M( R - or S -N^O) 2 complexes (N^O = chiral deprotonated Schiff base ligands, M = Rh/Cu/Ni/Zn). − In the formation of tetrahedral or distorted tetrahedral/square-planar complexes containing two chiral N^O-chelate units, diastereoselectivity plays a major role because the resulting C 2 -symmetrical molecules may show preferential chirality at metal center (Λ- or Δ-configuration) induced by the ligand chirality. Thus, use of the enantiopure R - or S -N^O chelates can lead to the formation of diastereomeric pairs of Λ-M- R -N^O and Δ-M- R -N^O (or Δ-M- S -N^O and Λ-M- S -N^O) in a selective way, while the racemic R / S -N^O ligands give all four isomers.…”

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confidence: 99%

Synthesis, X-ray, and Spectroscopic Study of Dissymmetric Tetrahedral Zinc(II) Complexes from Chiral Schiff Base Naphthaldiminate Ligands with Apparent Exception to the ECD Exciton Chirality

et al. 2016

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Bidentate enantiopure Schiff base ligands, (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminate (R- or S-N^O), diastereoselectively provide Λ- or Δ-chiral-at-metal four-coordinated Zn(R- or S-N^O)2 {Ar = C6H5; Zn-1R or Zn-1S and p-C6H4OMe; Zn-2R or Zn-2S}. Two R- or S-N^O-chelate ligands coordinate to the zinc(II) in a tetrahedral mode and induce Λ- or Δ-configuration at the zinc metal center. In the solid state, the R- or S-ligand diastereoselectively gives Λ- or Δ-Zn configuration, respectively, and forms enantiopure crystals. Single crystal structure determinations show two symmetry-independent molecules (A and B) in each asymmetric unit to give Z' = 2 structures. Electronic circular dichroism (ECD) spectra show the expected mirror image relationship resulting from diastereomeric excess toward the Λ-Zn for R-ligands and Δ-Zn for S-ligands in solution. ECD spectra are well reproduced by TDDFT calculations, while the application of the exciton chirality method, in the common point-dipole approximation, predicts the wrong sign for the long-wavelength couplet. A dynamic diastereomeric equilibrium (Λ vs Δ) prevails for both R- and S-ligand-metal complexes in solution, respectively, evidenced by (1)H NMR spectroscopy. Variable temperature (1)H NMR spectra show a temperature-dependent shift of the diastereomeric equilibrium and confirm Δ-Zn configuration (for S-ligand) to be the most stable one and favored at low temperature. DSC analyses provide quantitative diastereomeric excess in the solid state for Zn-2R and Zn-2S, which is comparable to the results of solution studies.

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Section: Introductionmentioning

confidence: 99%

Synthesis, X-ray, and Spectroscopic Study of Dissymmetric Tetrahedral Zinc(II) Complexes from Chiral Schiff Base Naphthaldiminate Ligands with Apparent Exception to the ECD Exciton Chirality

et al. 2016

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“…Another cause for the difference in distribution between aand b-amino acids may arise from the different structures of the formed complexes with the host. The supposed bidentate interaction of the substrate with the palladium center 10 would result in a five membered ring for a-amino acids 14 and a six membered ring for b-amino acids, 15 which could lead to a difference in stability.…”

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confidence: 99%