The Role of Nitrogen Donors in Zinc Catalysts for Lactide Ring-Opening Polymerization

The electronic effects
of nitrogen donors in zinc catalysts for ring-opening polymerization
of cyclic esters were investigated. Alkyl and benzyloxy zinc complexes
supported by tridentate diamino- and aminoimino phenolate ligands
were synthesized, and their solid-state and solution structures characterized.
The solution-state structures showed that the alkyl complexes are
mononuclear, while the alkoxy complexes are dimeric with the ligands
coordinated with different denticities depending on the nature of
the ligand donors. The catalytic activities of these compounds toward
the ring-opening polymerization of racemic lactide were studied and
showed that catalysts with secondary and imine nitrogen donors are
more active than analogues with tertiary amines.