Ring-Opening Polymerization of ε-Caprolactone by Using Aluminum Complexes Bearing Aryl Thioether Phenolates: Labile Thioether Chelation

Someswara Rao Kosuru; Yu-Lun Chang; Po-Yu Chen; Wei Lee; Yi-Chun Lai; Shangwu Ding; Hsuan-Ying Chen; Hsing-Yin Chen; Yung-Chi Chang

doi:10.1021/acs.inorgchem.1c03683

Ring-Opening Polymerization of ε-Caprolactone by Using Aluminum Complexes Bearing Aryl Thioether Phenolates: Labile Thioether Chelation

Inorg Chem. 2022 Mar 7;61(9):3997-4008. doi: 10.1021/acs.inorgchem.1c03683. Epub 2022 Jan 12.

Authors

Someswara Rao Kosuru¹, Yu-Lun Chang¹, Po-Yu Chen¹, Wei Lee¹, Yi-Chun Lai¹, Shangwu Ding^{1

2}, Hsuan-Ying Chen^{1

2

3}, Hsing-Yin Chen¹, Yung-Chi Chang⁴

Affiliations

¹ Department of Medicinal and Applied Chemistry, Drug Development and Value Creation Research Center, Kaohsiung Medical University, Kaohsiung, Taiwan 80708, ROC.
² Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan 80424, ROC.
³ Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung 80708, Taiwan, ROC.
⁴ Leiden Institute of Chemistry, Faculty of Science, Leiden University, 2300 RA Leiden, The Netherlands.

PMID: 35020371
DOI: 10.1021/acs.inorgchem.1c03683

Abstract

In this study, aluminum complexes bearing ferrocene-based and arylthiomethylphenolate ligands were synthesized, and their catalytic activity for ε-caprolactone (CL) polymerization was investigated. The catalytic activity of the reduced form of Al complexes was higher than that of the oxidized form. The CL polymerization rate of the reduced form fcO₂AlMe (75 min, conversion = 100%) was higher than that of the oxidized form fc^oxO₂AlMe (4320 min, conversion = 45%), and the CL polymerization rate of fc(OAlMe₂)₂ (40 min, conversion = 100%) was higher than that of fc^ox(OAlMe₂)₂ (60 min, conversion = 97%). Electron deficiency substituents on phenolate decreased the catalytic activity of Al complexes bearing arylthiomethylphenolate ligands. Density functional theory calculations revealed that thioether coordination stabilized the transition state (TS1) and that the oxidized form fc^ox(OAlMe₂)₂ exhibited weaker thioether coordination and higher activation energy in TS1 compared with those of the reduced form fcO₂AlMe. In addition, our study determined that the thioether group is a suitable chelating group for Al catalysts in CL polymerization due to its labile nature.