Synthesis and Structural Characterization of Group 4 Metal Alkoxide Complexes of <i>N</i>,<i>N</i>,<i>N</i>′<i>,N</i>′‑Tetrakis(2-hydroxyethyl)ethylenediamine and Their Use As Initiators in the Ring-Opening Polymerization (ROP) of <i>rac</i>-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 1H 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 °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 °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 Ti4(TOEED)­(OiPr)12 was demonstrated to convert over 95% of the rac-LA within 160 min.