Carbonyl group coordination preferences in square-planar NiII and PdII complexes of pentadentate ligands by electron-withdrawing/donating substituents

• Chirally switchable NiII and PdII complexes were designed containing different substitution patterns on the aromatic rings.
• Crystal structures of the complexes were determined by single crystal X-ray diffraction analysis.
• The coordination preference of the ligand sidearms was studied via DFT calculations.

A series of chirally switchable NiII and PdII complexes were synthesized and fully characterized by X-ray crystallography and additionally by NMR. It was found that control of the stereochemical preference between (S∗,S∗) and (S∗,R∗) diastereomers by substituent modification of the ligand sidearms was possible in the process of crystallization with the preferred coordination of the sidearms generally consistent with expectations based on the electron-donating or -withdrawing properties of the sidearm substituent groups. There were however, quite interesting and unanticipated exceptions counter to chemical intuition and it seems that only for complexes with ortho substituents are strong preferences for the coordination manner necessarily displayed in the solid state based on the electron-withdrawing or -donating properties of the substituents.

The sidearm substitution of chirally switchable NiII and PdII complexes does not perturb the macromolecular stereochemical order leading to quasidiastereomeric relationships. This allows for the design of substituent-controlled stereochemical preferences in the solid state and thus also the structural design of more advanced molecular systems with predictable macromolecular structure.Figure optionsDownload as PowerPoint slide