Stereochemistry of six-coordinated tungsten(VI) complexes having one rigid chiral bidentate ligand and two flexible bidentate ligands: Stereo-selective formation of Δ- and Λ-forms induced by the chiral ligand

Abstract

Six-coordinated tungsten(VI) complexes with one rigid chiral bidentate ligand, 1,1′-bi-2-naphthol (bino) 1, and two flexible bidentate ligands (f-bls), pinacol (pin) or ethylene glycol (en), were prepared, and their stereochemistry was discussed. Generally, metal complexes with three f-bls produce enantiomeric Δ- and Λ-forms. Other types of isomerism are produced by f-bls, which are attributable to their conformation, i.e., δ- and λ-forms. Although the conformational isomerism of Δ- and Λ-enantiomers produces diastereomers, the energy differences between the diastereomers are small, less than several kcal mol−1. Therefore, the conformational isomerism of f-bls is not significant in coordination chemistry. We found that the introduction of one rigid chiral bidentate ligand controls the Δ- and Λ-stereochemistry of the complex. The conformation of (R)-bino produces the Δ-isomer, and that of (S)-bino affords the Λ-isomer. We also performed theoretical studies to support our observations.