Diastereoselection and induced chirality at-metal in distorted-tetrahedral bis[(R or S)-1-(p-R₁-C₆H₄)-N-(phenyl(pyridin-2-yl)methylene)ethanamino-κ²N,N]-Δ/Λ-copper(PF₆)₂

Abstract

The enantiopure Schiff bases (R or S)-1-(p-R₁-C₆H₄)-N-(phenyl(pyridin-2-yl)methylene)ethanamine (R₁ = H and OCH₃) are synthesized from reaction between the 2-benzoyl-pyridine and chiral-amine (R or S)-1-(p-R₁-C₆H₄)ethylamine, respectively. These Schiff bases react with the copper(II) acetate to give distorted-tetrahedral bis[(R or S)-1-(p-R₁-C₆H₄)-N-(phenyl(pyridin-2-yl)methylene)ethanamino-κ²N,N]-Δ/Λ-Cu(PF₆)₂ in the presence of NH₄PF₆. A conformational change from cis- to trans-isomer occurs in solution and thereby, the copper(II) coordinates to the solely trans-form to provide the complexes. Cyclic voltammograms demonstrate two quasi-reversible one electron charge transfer processes for the Cu²⁺/Cu⁺ and Cu⁺/Cu⁰ couples in acetonitrile. ECD spectra reveal expected mirror-image relationships and indicate enantiopurity or enantiomeric excess of the R or S-ligands and their associated complexes in solution. Comparisons of experimental and simulated ECD spectra suggest induced chirality at-metal center, which diastereoselectively provides the Δ-Cu-R or Λ-Cu-S diastereomer as major product in solution. DFT/TDDFT optimized structures and excited state properties correspond well to the experimental results.

Keywords:

• Copper(II)-chiral-N,N-chelate Schiff bases
• induced chirality at-metal and diastereoselection
• chiroptical properties
• cis-to-trans interconversion
• DFT/TDDFT

Acknowledgements

We acknowledge Wazed Miah Science Research Centre (WMSRC) at Jahangirnagar University, Dhaka, Bangladesh for obtaining CV data. Our sincere thanks to Professor W. Houry and Mr. V. Bhandari, Department of Biochemistry, Faculty of Medicine, University of Toronto, for obtaining ECD spectra. We thank Professor C. Janiak, Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität Düsseldorf, Germany for many useful discussions. We are also grateful to Professor A.B.P. Lever, Department of Chemistry, York University, Toronto, and the Computecanada.ca (https://ccdb.computecanada.ca/) Ontario, Canada for using computational resources.

Disclosure statement

No potential conflict of interest was reported by the authors.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.