Titanium complexes containing tridentate [ONO] type Schiff base ligands for the cycloaddition reaction of CO2 to propylene oxide

Abstract

New titanium complexes, TiLCl2(THF) and TiL2, containing the tridentate chiral Schiff-base ligand, L, prepared from the condensation reaction of 2,4-pentadione and (1R,2S)-(−)-1-aminoindanol, were synthesized and characterized by various analytical methods including X-ray crystallography. Ligand L acted as a dianionic tridentate ligand and, owing to a chiral center in the aminoindanol part, imparted chirality to its titanium complexes. The newly synthesized titanium complexes and previously reported analogous Ti complexes were used as catalysts in the cycloaddition of CO2 to propylene oxide as the first representatives of titanium complexes with tridentate Schiff base ligands to have been used for this purpose. These complexes provided high selectivity toward cyclic propylene carbonate (>99%) and showed considerable activities with TOF values up to 131 h−1 in comparison with the previously reported catalyst systems.