Titanium complexes containing bidentate benzotriazole ligands as catalysts for the ring opening polymerization of lactide

Abstract

The selective syntheses of titanium complexes containing the 2-(2H-benzo[d][1,2,3]triazol-2-yl)-4,6-ditert-pentylphenol (LH) ligand, namely [LTiCl2(mu-Cl)](2) (1), LTiCl3(THF) (2), L2Ti(NMe2)2 (3), L2TiCl2 (4) and L2Ti(O-i-Pr)2 (5), were achieved by changing the solvents or metal precursors. The solid state structures of 1-5 were revealed by single-crystal X-ray analyses. Complexes 2 and 5 showed a fast thermal exchange process of the benzotriazole ligand L. Among 1-5, complex 5 was proven as a highly effective catalyst for the controlled ring opening polymerization (ROP) of lactide (LA), as shown by the linearity of the molecular weight versus [LafTij ratio as well as very narrow PDI values of the PLA polymers obtained.