On July 28, the research group of Prof. Xie Xiaolin published an online paper entitled "Cobalt-Mediated Switchable Catalysis for One-Pot Synthesis of Cyclic Polymers (Angew Chem Int Ed 2021, 60, 16974-16979)" on Angewandte Chemie International Edition. This is another major progress in the field of biodegradable polymers.
In this paper, the first example of a switchable catalytic system that involves ring-opening copolymerization of epoxides/anhydrides/CO2 and photo-induced intramolecular radical addition has been demonstrated. It enabled the direct synthesis of well-defined cyclic polyesters and cyclic CO2-based polycarbonates from mixtures of monomers in an efficient process.
The key to this protocol is the rational design of a cobalt salen pentenoate catalyst [(salen)CoIII-OPe], whereby the ROCOP active species α-alkene-ω-O-CoIII(salen) can be quantitatively and quickly transformed into α-alkene-ω-O2C-CoIII(salen) linear precursors via migratory insertion of CO into Co-O bonds. Upon dilution of the reaction mixture, the homo-cleavage of Co-C bonds induced by visible light generates α-alkene acryl radicals that spontaneously undergo radical cyclization reaction. The resulting organocobalt incorporated cyclic polymers can serve as macroinitiator for OMRP of vinyl monomer to give facile access to tadpole-shaped polymers. Alternatively, it can react with radical scavengers such as thiol compounds to afford metal-free cyclic polymers. Notably, the modal reaction of 3-buten-1-yloxycarbonyl cobalt salen complex is suggestive of excellent regioselectivity and chemoselectivity of the radical addition reaction. This work demonstrates the possibility to synthesize cyclic polyesters with diverse functionality directly from monomer mixtures via a RC approach.
Huazhong University of Science and Technology (HUST) is the signature unit of the first author. Doctoral student Zhao Yajun is the first author; Doctoral students Zhu Shuaishuai, Bachelor student Liao Can, Prof. Xie Xiaolin, Prof. Zhou Xingpin from the School of Chemistry and Chemical Engineering (HUST), as well as Prof. Wang Xianhong from Changchun Institute of Chemical Engineering (Chinese Academy of Sciences), Academician Tang Benzhong and Prof. Lin Rongye from Hongkong University of Science and Technology are the co-authors of the paper. Postdoc researcher Wang Yong is the corresponding author. This work is sponsored by National Key R&D Plan (No.2016YFB0302400), NSFC (No.21604027) of China.
Link to the paper: https://onlinelibrary.wiley.com/doi/10.1002/anie.202106285
