Dinucleating Ligand Platforms Supporting Indium and Zinc Catalysts for Cyclic Ester Polymerization

Abstract

The synthesis of the first alkoxide-bridged indium complex supported by a chiral dinucleating ligand platform (<b>1</b>), along with its zinc analogue (<b>2</b>), is reported. Both complexes are synthesized in a one-pot reaction starting from a chiral dinucleating bis­(diamino)­phenolate ligand platform, sodium ethoxide, and respective metal salts. The dinucleating indium analogue (<b>7</b>) based on an achiral ligand backbone is also reported. Indium complexes bearing either the chiral or achiral ligand catalyze the ring-opening polymerization of racemic lactide (<i>rac</i>-LA) to afford highly heterotactic poly­(lactic acid) (PLA; <i>P</i>_r > 0.85). The indium complex bearing an achiral ligand affords essentially atactic PLA from <i>meso</i>-LA. The role of the dinucleating ligand structure in catalyst synthesis and polymerization activity is discussed