Synthesis of dinuclear aluminum complexes bearing bis-phenolate ligand and application in ring-opening polymerization of ε-caprolactone

The stoichiometric reaction of bis-phenolate ligands with AlMe3 afforded zwitterionic aluminum complexes Al1-Al3, which were characterized by NMR spectroscopy and elemental analysis. The solid state structure of Al2 was determined by single-crystal X-ray diffraction, which revealed a dinuclear feature. Two Al centers were bridged by two ligands and thus formed an unusual large 24-memberedring metallacycle. In the presence of BnOH, Al1-Al3 were efficient for the ring-opening polymerization of epsilon-caprolactone in a controlled manner, and the efficiency was affected by substituents on the ligands. The polymerizations exhibited a feature of immortal catalysis with an excess of BnOH.