Center for Molecular Systems and Organic Devices, Institute of Optoelectronic Materials, Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts and Telecommunications , 9 Wenyuan Road, Nanjing 210023, China.
Department of Chemical Engineering, Virginia Polytechnic Institute and State University , 635 Prices Fork Road, Blacksburg, Virginia 24061, United States.
J Am Chem Soc. 2017 May 3;139(17):6177-6182. doi: 10.1021/jacs.7b01462. Epub 2017 Apr 19.
Poly(α-hydroxy acids) are important biodegradable polymers with wide applications. Attempts to synthesize them from O-carboxyanhydrides with pendant functional groups by various methods, including methods involving organocatalysts or organometallics, have been plagued by uncontrolled polymerization, including epimerization for some monomers, which hampers the preparation of stereoregular high-molecular-weight polymers. Herein we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic polyesters with expected molecular weights (>140 kDa) and narrow molecular weight distributions (M/M < 1.1). Mechanistic studies indicate that the use of a low temperature (-20 °C) and photoredox Ni/Ir catalysis synergistically accelerates ring-opening and decarboxylation of the monomer for chain propagation while avoiding the formation of the undesired Ni-carbonyl complex.
聚（α-羟基酸）是一类重要的可生物降解聚合物，具有广泛的应用。人们尝试通过各种方法，包括使用有机催化剂或有机金属试剂的方法，从带有侧基官能团的 O-羧酸酐出发来合成它们，但这些方法都受到不可控聚合的困扰，包括某些单体的差向异构化，这阻碍了具有规整结构的高分子量聚合物的制备。在此，我们描述了一种有效的方案，将光氧化还原 Ni/Ir 催化与 Zn-醇盐的使用相结合，用于高效开环聚合，从而可以合成具有预期分子量（>140 kDa）和较窄分子量分布（M/M < 1.1）的等规聚酯。机理研究表明，低温（-20°C）和光氧化还原 Ni/Ir 催化的协同作用可以加速单体的开环和脱羧反应，从而促进链增长，同时避免形成不希望的 Ni-羰基配合物。
