(S)-N-[(2-hydroxynaphthalen-1-yl)methylidene]valine – A valuable ligand for the preparation of chiral complexes

A chiral tridentate ONO Schiff base ligand has been prepared from valine and o-hydroxynaphthaldeyhde. The reactions of this ligand with organoelement halides from group 4 and 14 lead to chiral pentacoordinate and hexacoordinate complexes. The electron density distribution around the central atoms has been investigated with solid state NMR and quantum chemical methods. [Display omitted] •Chiral tridentate Schiff base ligand from l-valine and 2-hydroxy-1-naphthaldehyde.•Pentacoordinate and hexacoordinate complexes with group 4 and 14 elements.•Stronger distortion of trigonal bipyramid from Si to Ge to Sn in pentacoordination.•Combined NMR-DFT-analysis of electron density distribution around the central atoms. The reaction of (S)-N-[(2-hydroxynaphthalen-1-yl)methylidene]valine (H2L), 1, with organoelement halides from group 4 and 14 leads to different hypercoordinated complexes depending on the substitution of the starting material. The dianion of 1 therein acts as tridentate ligand in κ3O,N,O’ coordination mode. Complexes with silicon, germanium, tin, and titanium have been prepared in that way and are presented here as proof of concept. With one exception diorganoelement chlorides R2ECl2 yield pentacoordinate complexes LER2. Element tetrachlorides yield hexacoordinate complexes L2E. The prepared compounds were characterized via NMR, IR and UV/Vis spectroscopy, elemental and X-ray structure analysis. Furthermore solid state NMR measurements and chemical shift tensor analysis with the help of quantum chemical methods were used to investigate the electron density distribution around the central atoms of several products. This study demonstrates the ability of 1 to form chiral hypercoordinate complexes with different elements.