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

The synthesis of the first alkoxide-bridged
indium complex supported by a chiral dinucleating ligand platform
(1), along with its zinc analogue (2), 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 (7) 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 (rac-LA) to afford highly heterotactic poly­(lactic acid)
(PLA; Pr > 0.85). The indium complex
bearing an achiral ligand affords essentially atactic PLA from meso-LA. The role of the dinucleating ligand structure in
catalyst synthesis and polymerization activity is discussed.