Theoretical Mechanistic Studies on Redox-Switchable Polymerization of Trimethylene Carbonate Catalyzed by an Indium Complex Bearing a Ferrocene-Based Ligand

The
redox-switchable mechanism of trimethylene carbonate (TMC)
polymerization catalyzed by an indium complex bearing a ferrocene-based
alkoxide phosfen chelating ligand has been elucidated by density functional
theory (DFT) calculations. Having achieved agreement between computational
results and available experimental findings, it is found that the
ring-opening of TMC moiety has higher energy barrier than that for
migratory insertion and serves as a rate-determining step of the polymerization
reaction. In comparison with the reduced state of the indium complex,
the experimentally observed higher activity of the oxidized form could
attribute to the oxidation-induced elongation and thus weakening of
the In–N bond of the complex, which strengthened the interaction
between the TMC unit and indium metal center and hence stabilized
the corresponding transition states. Such geometry and binding changes
upon oxidation are manifested by the analyses of structure, bond indexes,
and energy decomposition.