Electronic Tuning of Iminotriphenolate Ligands for Titanium(IV)-catalyzed Ring-opening Copolymerization of Cyclic Anhydrides and Epoxides

Abstract

Alternating ring-opening copolymerization (ROCOP) is a versatile synthetic method for preparing polyesters using relatively inexpensive and readily available monomers, epoxides and cyclic anhydrides. In this study, a new type of titanium (IV) complex coordinated with iminophenolate ligands was developed as an efficient catalyst for alternating ROCOP. As found in the crystal structures, iminophenolate titanium (IV) complexes exhibited octahedral geometries owing to geometrical constraints. Electronic tuning of iminophenolate ligands revealed that chloro-substituted ligands are more efficient than other ligands with electron-withdrawing or electron-donating ligands. Density functional theory computation provided reaction profiles where octahedral intermediates and transition states were stabilized, and the chlorine substituent was the most efficient in stabilizing the transition state for the epoxide opening step.