Reversible On/Off Switching of Lactide Cyclopolymerization with a Redox-Active Formazanate Ligand

Redox-switching of
a formazanate zinc catalyst in ring-opening
polymerization (ROP) of lactide is described. Using a redox-active
ligand bound to an inert metal ion (Zn2+) allows modulation
of the catalytic activity by reversible reduction/oxidation chemistry
at a purely organic fragment. A combination of kinetic and spectroscopic
studies, together with mass spectrometry of the catalysis mixture,
provides insight in the nature of the active species and the initiation
of lactide ring-opening polymerization. The mechanistic data highlight
the key role of the redox-active ligand and provide a rationale for
the formation of cyclic polymer.