Tetranuclear N-Methyl Aminodiethylate Aluminum Complexes as Efficient Catalysts for Ring-Opening Polymerization of Substituted Epoxides

Abstract

Polyether materials, derived from the ring-opening polymerization (ROP) of epoxides, are widely used in biomedicine and functional materials. However, due to the steric hindrance of the high-freedom substituents, monosubstituted epoxides are difficult to activate and exhibit the characteristics of being difficult to polymerize. In addition, traditional anionic ring-opening polymerization (AROP) usually has functional group tolerance problems. As such, it is of great significance to develop efficient catalytic systems to achieve the polymerization of monosubstituted epoxides. In this work, a series of tetranuclear aluminum complexes [Al(R¹)₃(ONO)AlR²]₂ (ONO = N-methyl aminodiethylate ligand) featuring the neutral AlR₃ molecules coordinated to oxygen atoms on ligand framework have been synthesized and characterized. These complexes can efficiently catalyze cyclohexene oxide (CHO) polymerization through the synergistic effect between aluminum metals, and the iso-butyl substituted tetra-aluminum complex [Al(ⁱBu)₃(ONO)Al(ⁱBu)]₂ shows the highest reactivity (TOF of 3792 h^–1) at 30 °C. Notably, this tetranuclear catalyst demonstrates exceptional catalytic activity in the polymerization of monosubstituted epoxide substrates. Mechanistic investigations elucidate the distinct roles of the aluminum centers in the synergistic catalytic systems for the first time: the neutral AlR₃ moiety serves as the initiator for ROP, whereas the Al–R group functions as a Lewis acidic activator that facilitates epoxide monomer activation. This study provides important guidance for the controlled synthesis of polyether architectures from monosubstituted epoxide precursors.

Keywords

Aluminum complex / Epoxide / Ring-opening polymerization / Polyether / Synergistic catalysis / N,O ligands / Homogeneous catalysis / Tetranuclear

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2025 SIOC, CAS, Shanghai, & WILEY-VCH GmbH