Characterization of Diastereomeric Equilibria of Pseudotetrahedral Bis[(R or S)‐N‐1‐(Ar)Ethylsalicylaldiminato‐κ²N,O]zinc(II) with Λ/Δ‐Chirality‐At‐Metal Induction

Abstract

A family of bis[(R or S)‐N‐1‐(Ar)ethylsalicylaldiminato‐κ2N,O]‐Δ/Λ‐zinc(II) {Ar=C6H5 (ZnRL1 or ZnSL1), p‐CH3OC6H4 (ZnRL2 or ZnSL2) and p‐ClC6H4 (ZnRL3 or ZnSL3)} compounds was synthesized and investigated by multiple methods. They feature Λ/Δ‐chirality‐at‐metal induction along the pseudo‐C2 axis of the molecules. The chirality induction is quantitative in the solid state, explored by X‐ray crystallography and powder X‐ray diffraction (PXRD), where R or S‐ligated complexes diastereoselectively yield Λ or Δ‐configuration at the metal. On the other hand, Λ and Δ‐diastereomers co‐exist in solution. The Λ⇆Δ equilibrium is solvent‐ and temperature‐dependent. Electronic circular dichroism (ECD) spectra confirm the existence of a diastereomeric excess of Λ‐ZnRL1−3 or Δ‐ZnSL1−3 in solution. DSC analysis reveals thermally induced irreversible phase transformation from a crystalline solid to an isotropic liquid phase. ECD spectra were reproduced by DFT geometry optimizations and time‐dependent DFT (TD‐DFT) calculations, providing ultimate proof of the dominant chirality atmetal in solution.