1345892-25-2Relevant academic research and scientific papers
Chirality and diastereoselection of Δ/?-configured tetrahedral zinc complexes through enantiopure Schiff base complexes: Combined vibrational circular dichroism, density functional theory, 1H NMR, and X-ray structural studies
Chamayou, Anne-Christine,Lüdeke, Steffen,Brecht, Volker,Freedman, Teresa B.,Nafie, Laurence A.,Janiak, Christoph
, p. 11363 - 11374 (2011)
The metal-centered Δ/?-chirality of four-coordinated, nonplanar Zn(A^B)2 complexes is correlated to the chirality of the bidentate enantiopure (R)-A^B or (S)-A^B Schiff base building blocks [A^B = (R)- or (S)-N-(1-(4-X-phenyl)ethyl) salicylaldiminato-κ2N,O with X = OCH3, Cl, Br]. In the solid-state the (R) ligand chirality induces a ?-M configuration and the (S) ligand chirality quantitatively gives the Δ-M configuration upon crystallization as deduced from X-ray single crystal studies. The diastereoselections of the pseudotetrahedral zinc-Schiff base complexes in CDCl3 solution were investigated by 1H NMR and by vibrational circular dichroism (VCD) spectroscopy. The appearance of two signals for the Schiff-base -CH=N- imine proton in 1H NMR indicates an equilibrium of both Δ- and ?-diastereomers with a diastereomeric ratio of roughly 20:80% for all three ligands. VCD proved to be very sensitive to the metal-centered Δ/?-chirality because of a characteristic band representing coupled vibrations of the two ligand's C=N stretch modes. The absolute configuration was assigned on the basis of agreement in sign with theoretical VCD spectra from Density Functional Theory calculations.
