Synthesis and characterization of TiL2 complexes with tridentate (ONO) (S)-NOBIN Schiff-base ligands

Abstract

Tridentate (ONO) C[subscript 1]-symmetric Schiff base ligands were synthesized by the condensation of (S)-2-amino-2'-hydroxy-1,1'-binaphthyalene with 4-hydroxy-3-phenanthrenecarboxaldehyde or 1-hydroxybenz[a]anthracene-2-carboxaldehyde. C[subscript 2]-symmetric titanium(IV) Schiff base complexes, TiL[subscript 2], were synthesized and characterized with these ligands. The complex with the benz[a]anthryl unit crystallizes in a facial coordination mode, OC-6-1'3'-C, whereas complex with phenanthryl unit crystallizes in a meridional mode, OC-6-22'-A. A comparison between the complexes and the ligands were done in solution using circular dichroism spectroscopy. Preliminary catalytic studies showed that these complexes can catalyze asymmetric carbonyl-ene addition reactions of 2-methoxypropene with aromatic aldehydes with moderate selectivity. The ligands and complexes were characterized by NMR, HRMS, single crystal X-ray diffraction and CD spectroscopy.