Titanium complexes containing new dianionic tetradentate [ONNO]-type ligands with benzyl substituents on bridging nitrogen atoms: Syntheses, X-ray structures, and catalytic activities in ring opening polymerization of lactide

Several titanium isopropoxides 1–8 have been prepared by the reaction of Ti(O-i-Pr)4 with a series of corresponding tetradentate Salan-type [ONNO] ligands with benzyl or methyl substituents on bridging nitrogen atoms. They have been characterized by 1H NMR, 13C{1H} NMR, and elemental analysis. Solid state structures of compounds 2, 4, 6, and 7 have been determined by X-ray crystallography. X-ray diffraction analysis and 1H NMR confirmed that these titanium complexes were all monomeric species with a six-coordinated central titanium in their solid and solution structures. Complexes 2, 4, 6, and 8 with benzyl substituents on bridging nitrogens gave PLA with higher molecular weight than compounds 1, 3, 5, and 7 with methyl substituents did.

Several types of titanium complexes 1–8 containing various substituted Salan-type [ONNO] ligands (Lig1–Lig8) were synthesized. The substituents on phenyl ring and Salan ligand backbone exerted significant influence upon the catalytic activity and molecular weight of PLA polymers obtained.Figure optionsDownload as PowerPoint slide