Synthesis, X-ray structures, and controlled ring opening polymerization behavior of l-lactide using titanium complexes chelated by tetradentate diamine–diethanolate ligand

Abstract

The synthesis and characterization of LTi(O-i-Pr)₂ (1) and LTiCl₂ (2) complexes containing a new [ONNO]-type tetradentate diamine–diethanolate ligand such as (HOCMe₂CH₂NMeCH₂CH₂NMeCH₂CMe₂OH) (LH₂2) was achieved. Single-crystal X-ray analyses revealed that monomeric complexes 1 and 2 had pseudo-C₂ and pseudo-C₁ symmetric distorted octahedral geometry, respectively. Interestingly, complex 1 has fac–fac geometry for tetradentate L around a Ti centre in both solid and solution, whereas complex 2 has different geometry in solid (mer–fac, C₁) and solution (fac–fac, C₂). They are effective catalysts for the controlled ring opening polymerization of L-lactide, as shown by the linearity of the number average of the molecular weight of polylactides versus conversion, as well as narrow PDI values.