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.

Graphical abstractSeveral 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 full-size imageDownload as PowerPoint slide