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.