N-(2-(Diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydro-quinolin-8-amines iron(ii) complexes: structural diversity and the ring opening polymerization of ε-caprolactone

Yun Wang; Wenjuan Zhang; Xing Wang; Weiwei Zuo; Xiaopan Xue; Yanping Ma; Wen-Hua Sun

doi:10.1039/d3ra05867k

N-(2-(Diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydro-quinolin-8-amines iron(ii) complexes: structural diversity and the ring opening polymerization of ε-caprolactone

RSC Adv. 2023 Oct 12;13(43):29866-29878. doi: 10.1039/d3ra05867k. eCollection 2023 Oct 11.

Authors

Yun Wang^{1

2

3}, Wenjuan Zhang^{1

2}, Xing Wang^{2

3}, Weiwei Zuo¹, Xiaopan Xue², Yanping Ma³, Wen-Hua Sun³

Affiliations

¹ State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University Shanghai 201620 China zhangwj@bift.edu.cn zuoweiwei@dhu.edu.cn.
² Beijing Key Laboratory of Clothing Materials R&D and Assessment, Beijing Engineering Research Center of Textile Nanofiber, School of Materials Science and Engineering, Beijing Institute of Fashion Technology Beijing 100029 China zhangwj@bift.edu.cn.
³ Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences Beijing 100190 China whsun@iccas.ac.cn.

Abstract

A series of N-(2-(diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydroquinolin-8-amines was prepared and used in individually reacting with iron chloride under nitrogen atmosphere to form their iron(ii) complexes Fe1-Fe6. All compounds were characterized using FT-IR spectroscopy and elemental analyses, the organic compounds were confirmed with NMR measurements, and the iron complexes were submitted to single-crystal X-ray diffraction, revealing Fe1, Fe2, Fe4, Fe5, and Fe6 as either mono- or di-nuclear forms. Forming a binary system in situ with two equivalents of LiCH₂SiMe₃, all iron complexes Fe1-Fe6 efficiently initiated the ring opening polymerization of ε-caprolactone, achieving the TOF up to 8.8 × 10³ h^-1. More importantly, the resultant polycaprolactone (PCL) possessed high molecular weights with the M_n range of 9.21-24.3 × 10⁴ g mol^-1, being a rare case of the iron(ii) catalyst in producing PCL with such high molecular weight. The ¹H NMR and MALDI-TOF investigations demonstrated that the PCLs were linear features capped with a methoxy group or CH₂SiMe₃ or cyclic structure that varied with the molar ratio of [ε-CL]/Fe.