Synthesis and Characterization of N,N,O-Tridentate Aminophenolate Zinc Complexes and Their Catalysis in the Ring-Opening Polymerization of Lactides.

Wei-Yi Lu,Kuo-Hui Wu,Chu-Chieh Lin,Hsuan-Ying Chen

doi:10.3389/fchem.2019.00189

Wei-Yi Lu, Kuo-Hui Wu + Show 2 more

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https://doi.org/10.3389/fchem.2019.00189

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Abstract

A series of aminophenolate ligands with various pendant groups and associated ethyl Zn complexes were synthesized and studied as catalysts for the ring-opening polymerization (ROP) of lactides (LAs). The thiophenylmethyl group (L4ZnEt) increased the catalytic activity more than the benzyl group (L1ZnEt) did, and 2-fluorobenzyl (L3ZnEt) and 2-methoxybenzyl (L2ZnEt) groups had the opposite effect. In addition, the LA polymerization mechanism proved by Nuclear Magnetic Resonance and Density Function Theory was that LA was attracted by H···O bond of an α-hydrogen of the LA molecule and the phenoxyl oxygen of the catalyst. After the dissociation of amino group from the Zn atom, the benzyl alcohol initiated LA without replacing the ethyl group of Zn complex. It is the first case where the ethyl group is regarded as a ligand and cannot be replaced by benzyl alcohol, and this information is very important for the mechanism study of ROP.

Highlights

Because petrochemical polymers such as polystyrene, polypropylene, polyethylene, and poly(vinyl chloride) can be produced and cheaply, they are widely used as disposable packaging materials
The Zn complex synthesis can be identified by the 1H Nuclear Magnetic Resonance (NMR) spectrum
The results revealed that the thiophenylmethyl group of L4ZnEt increased the catalytic activity of Zn complexes more than the benzyl group of L1ZnEt did, and that 2-fluorobenzyl and 2-methoxybenzyl groups decreased the catalytic activity of the complexes

Summary

Introduction

Because petrochemical polymers such as polystyrene, polypropylene, polyethylene, and poly(vinyl chloride) can be produced and cheaply, they are widely used as disposable packaging materials. The X-ray structure of L1ZnEt (CCDC 1574177), Figure 3 revealed a four-coordinated, mononuclear Zn complex with one ethyl group and one aminophenolate ligand.

Results

Conclusion