Yang Guan-Wen, Zhang Yao-Yao, Xie Rui, Wu Guang-Peng
MOE Laboratory of Macromolecular Synthesis and Functionalization, Adsorption and Separation Materials and Technologies of Zhejiang Province, Department of Polymer Science and Engineering, Zhejiang University, Zhe Da Road 38, Hangzhou, 310027, China.
Angew Chem Int Ed Engl. 2020 Sep 21;59(39):16910-16917. doi: 10.1002/anie.202002815. Epub 2020 Jul 27.
This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring-opening polymerization (ROP) of epoxides under mild conditions. The bifunctional catalyst incorporates two 9-borabicyclo[3.3.1]nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>10 g mol ). Based on the investigations on crystal structure of catalyst, MALDI-TOF, and B NMR spectroscopy, an intramolecular ammonium cation assisted S 2 mechanism is proposed and verified by DFT calculations.
本手稿描述了一种具有前所未有的反应活性的双功能有机催化剂，用于在温和条件下通过环氧化物的开环聚合（ROP）合成聚醚。该双功能催化剂在两端包含两个9-硼双环[3.3.1]壬烷中心作为用于环氧化物活化的路易斯酸性位点，在中间包含一个卤化季铵作为引发位点。该催化剂可以很容易地从市售原料分两步制备，规模可达千克级，产率约为100%。有机硼催化剂介导的环氧化物ROP在低催化剂负载量（5 ppm）下表现出活性聚合行为，并能够合成分子量超过百万克每摩尔（>10 g mol）的聚醚。基于对催化剂晶体结构、基质辅助激光解吸电离飞行时间质谱（MALDI-TOF）和硼核磁共振（¹¹B NMR）光谱的研究，提出了一种分子内铵阳离子辅助的双分子亲核取代（SN2）机理，并通过密度泛函理论（DFT）计算进行了验证。
