Pseudotetrahedral Zn(ii)-(R or S)-dihalogen-salicylaldiminato complexes with ?- or Δ-chirality induction at-metal

Reactions of enantiopure (S or R)-N-1-(phenyl)ethyl-2,4-X-1,X-2-salicylaldimine (S-H or R-H; X-1, X-2 = dihalogen) with Zn(ii)-nitrate give bis[(S or R)-N-1-(phenyl)ethyl-2,4-X-1,X-2-salicylaldiminato-kappa N-2,O]-zinc(ii), (Delta-ZnS or ?-ZnR) with Delta/?-chirality induction at-metal in the C-2-symmetric molecules. EI-mass spectra show parent ion peaks. X-ray structures indicate that two phenolate-oxygen and two imine-nitrogen atoms from two molecules of the Schiff bases coordinate to the Zn(ii) ion in a pseudotetrahedral geometry. Structural analyses give evidence that the S- or R-ligand chirality gives only one diastereomer Delta-ZnS or ?-ZnR in an enantiopure crystal. Gas-phase optimized structures suggest that the Delta-ZnS or ?-ZnR diastereomers are slightly more stable than ?-ZnS or Delta-ZnR by 1-2 kcal mol(-1). The intramolecular interactions were analyzed with the Independent Gradient Model (IGM) using the program Multiwfn on the optimized structures and also indicate the diastereomeric preference of Delta-ZnS1 over ?-ZnS1 (or ?-ZnR1 over Delta-ZnR1). Variable time and temperature H-1 NMR spectra support the presence of only one diastereomer ?-ZnR or Delta-ZnS in the bulk samples, backed by the simulated spectra which exhibit no diastereomerization in solution. In contrast, the reported Zn(ii)-(R or S)-salicylaldiminato/naphthaldiminato complexes show a diastereomeric mixture of both Delta- and ?-forms and a Delta reversible arrow ? equilibrium in solution. Electronic circular dichroism (ECD) spectra in solution display expected mirror-image relationships for the (S or R)-Schiff base ligands and the (S or R)-ligated complexes. Combined analyses of experimental and simulated ECD spectra further support the notion of diastereomeric excess of Delta-ZnS or ?-ZnR in solution. The overall results thus suggest the preservation of chirality at-zinc induced by S- or R-ligands in a solid or solution. Supramolecular packing analyses explore different kinds of intermolecular interactions with the strongest one for XMIDLINE HORIZONTAL ELLIPSISO. Only the halogen atom in the para position is involved in these interactions with BrMIDLINE HORIZONTAL ELLIPSISO > ClMIDLINE HORIZONTAL ELLIPSISO. Hirshfeld surface analyses also support these interactions between two molecules at a distance shorter than the sum of the vdW radii. Comparison of the experimental and simulated PXRD patterns from the single-crystal X-ray structures shows a good matching and confirms the phase purity of the bulk samples.

Automated summary

The experimental results suggest the preservation of chirality induced by S- or R-ligands at zinc in both solid and solution, with a tendency towards enantiomeric excess. Supramolecular packing analyses and Hirshfeld surface analyses support different types of intermolecular interactions, while comparison of experimental and simulated PXRD patterns shows a good match, confirming the phase purity of the samples.