The role of Lewis acidity in bis(β-diketonate)zirconium(IV) complexes as catalysts for the ring-opening polymerization of δ-valerolactone

Abstract

Poly(δ-valerolactone) (PVL) is a polymer that has garnered significant researcher interest due to its intriguing features and prospective uses across numerous domains, particularly in medicine. This work aimed to assess the influence of the Lewis acidity of the bis(β-diketonate)Zr catalyst complex on the ring-opening polymerization of δ-valerolactone. The ligand in the compound contains an electron-donating group, specifically the methyl group (2a). Furthermore, electron-withdrawing groups employed include phenyl (2b–2c) and trifluoromethyl groups (2d). Characterization data indicate that PVL has been successfully synthesized with a bis(β-diketonate)Zr complex catalyst. The hierarchy of Lewis acid strength for the bis(β-diketonate)Zr complex is 2c > 2b > 2d ≫ 2a. The sequence of PVL DP from highest to lowest is 2b, 2c, 2d and 2a. Nonetheless, the elevated Lewis acidity of complex 2c does not provide PVL with the greatest degree of polymerization. The steric barrier of complex 2c, which contains two phenyl groups, is larger than that in complex 2b. Consequently, the coordination process of the nucleophilic monomer with the electrophilic zirconium central atom becomes increasingly difficult.