Synthesis and Structural Characterization of Group 4 Metal Alkoxide Complexes of N,N,N′,N′-Tetrakis(2-hydroxyethyl)ethylenediamine and Their Use As Initiators in the Ring-Opening Polymerization (ROP) of rac-Lactide under Industrially Relevant Conditions

A series of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (TOEEDH4) ligand precursors and their group 4 metal complexes have been prepared. The complexes have been characterized by single-crystal X-ray diffraction and H-1 NMR spectroscopy, highlighting the ability to systematically vary the number of TOEED ligands within the system. Initial catalytic data for the solvent-free, ring-opening polymerization of rac-lactide (rac-LA), a promising degradable polymer produced from renewable resources, is reported. At 135 degrees C, it has been demonstrated that the activity of the complexes is enhanced by increasing the number of labile isopropoxide groups. When the temperature was further increased to 165 degrees C, all complexes demonstrated a far higher activity irrespective of the identity of the metal or number of labile initiator groups. Polymerization kinetics were monitored in real time using FT-IR spectroscopy with a diamond composite insertion probe and Ti-4(TOEED)((OPr)-Pr-i)(12) was demonstrated to convert over 95% of the rac-LA within 160 min.