Lactide as the Playmaker of the ROP Game: Theoretical and Experimental Investigation of Ring-Opening Polymerization of Lactide Initiated by Aminonaphtholate Zinc Complexes

A family of homo-
and heteroleptic zinc complexes bearing aminonaphtholate ligands was
synthesized and fully characterized. Using NMR spectroscopy and DFT
calculation, bis-alkoxy-bridged complexes [LZn­(μ-OR)]2 were confirmed to have dimeric structures in solution, analogous
to those obtained via X-ray crystallography. Surprisingly, a detailed
experimental and theoretical study of the catalytic activity of [LZn­(μ-OR)]2 in the ring-opening polymerization (ROP) of lactides showed
that although well-defined alkoxy dimers possess a single-site structural
motif, the most active initiator is obtained during in situ alcoholysis
of the alkylzinc precursor. These results indicate that rational ancillary
and alkoxy ligand design that takes into account its mutual interaction
on monomer coordination may be key to the synthesis of new high-performance
ROP catalysts.