Work

Structural and Kinetics Studies of N^O‐, O^N^O‐, and N^N‐ Schiff Base Mn Complexes as Highly Active Catalysts in the Ring‐Opening Polymerization of rac‐Lactides

Year: 2025

Type: article

Abstract: A series of manganese complexes derived from (imino)phenol/pyridine proligands have been synthesized, structurally characterized and used as catalysts in the ring‐opening polymerization (ROP) of rac‐lactides (rac‐LA). Reactions of MnCl2·4H2O salt with 2‐[((2‐hydroxyethyl)imino)methyl]phenol (L1H2) afford a tetranuclear Mn(III) complex [Mn(L1)Cl]4 (Mn1). Separately, treatment of MnCl2·4H2O with 2‐[((2‐methoxyethyl)imino)methyl]phenol (L2H) gave the mononuclear Mn(II) complex [Mn(L2)2(CH3OH)2] (Mn2). Further, reactions of (imino)pyridine proligands ((E)‐2‐((pyridine‐2‐ylmethylene)amino)ethan‐1‐ol (L3H) and (E)‐N‐(2‐methoxyethyl)‐1‐(pyrid‐2‐yl)methanimine (L4)) with MnCl2·4H2O afforded polynuclear Mn(II) complexes [Mn(L3H)Cl2]3 (Mn3) and [Mn(L4)Cl2]3 (Mn4), respectively. The molecular structure of Mn1 established the tridentate binding mode of the dianionic alkoxy‐(imino)phenol proligand ((L12−)) through the phenoxo and pendant‐arm alkoxy‐oxygen and the imine‐nitrogen atoms. In contrast, the molecular structure of Mn2 showed that the ether‐(imino)phenol pro‐ligand (L2H) is monoanionic (L2−) and bidentately coordinated to the Mn(II) metal center through the phenoxo‐oxygen and the imine‐nitrogen atoms. The dinuclear complex Mn3 contains a neutral N^N bidentately bound proligand (L3H). All the complexes (Mn1–Mn4) formed active catalysts in ROP of rac‐LA with the propagation rate constant kp of up to (4.25 ± 0.15) × 10−2 L mol−1 s−1. The polymers obtained were atactic biased (Pr = 0.55–0.59), produced with moderate control over average‐number molecular weights and were moderately dispersed (Đ up to 1.8) under melt conditions.

Source: European Journal of Inorganic Chemistry

DOI: 10.1002/ejic.202500126

Authors: Mnqobi Zikode, Asanda Ngwenya, Tabea Becker, Sonja Herres‐Pawlis, Stephen. O. Ojwach

Institutions: University of KwaZulu-Natal, RWTH Aachen University

Language: English

Topic: biodegradable polymer synthesis and properties

Subfield: Biomaterials

Field: Materials Science

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,050

Funders: Department of Science and Innovation, South Africa, RWTH Aachen University