Kinetic Study on the Coupling of CO2 and Epoxides Catalyzed by Co(III) Complex with an Inter- or Intramolecular Nucleophilic Cocatalyst
Kinetic Study on the Coupling of CO2 and Epoxides Catalyzed by Co(III) Complex with an Inter- or Intramolecular Nucleophilic Cocatalyst
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Co(III)配合物与分子间或分子内亲核助催化剂催化CO2与环氧化物偶联的动力学研究
DOI：
10.1021/ma302580s
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发表时间：
2013-02-26
期刊：
影响因子：
5.5
通讯作者：
Lu, Xiao-Bing
中科院分区：
文献类型：
--
作者：
Liu, Jie;Ren, Wei-Min;Lu, Xiao-Bing
水杨醛二胺三价钴配合物在分子间或分子内亲核助催化剂的存在下，已被证明是二氧化碳和环氧化物共聚的优良催化剂，以选择性地提供具有完美交替性质的相应的聚碳酸酯。特别是含有季铵盐的双官能团钴(III)-Salen络合物，即使在高温和极低的催化剂负载量下也能更有效地催化这种共聚。用原位红外光谱法研究了两种不同催化剂体系(Salen(III)X1/(Bu4NX)-Bu-n和含季铵盐的双功能催化剂2，X=2，4-二硝基苯氧基)在CO_2与环氧化物(环氧丙烷或环己烯)偶联反应中的反应动力学。在二元催化剂体系中很容易发现诱导期，诱导期的长度明显依赖于催化剂的负载量。相反，在双功能催化剂2中没有观察到诱导期，整个反应路径符合催化剂浓度的一级依赖关系。1/(Bu4NX)-Bu-n二元催化体系的反应级数为1.61，表明了共聚反应的复杂性。测定了二元催化剂1/(Bu4NX)-Bu-n体系催化二氧化碳和环氧丙烷偶联反应的环碳酸酯和共聚物生成的活化能分别为50.1和33.8kJ/mol，而双功能催化剂2的相应活化能分别为77.0kJ/mol和29.5kJ/mol。环状碳酸酯与共聚物形成的活化能的巨大差异是双功能催化剂体系即使在高温下也具有良好的共聚物形成选择性的原因。在CO_2与环氧环己烷偶联体系中，二元催化剂1/(Bu4NX)-Bu-n体系的共聚反应活化能为47.9kJ/mol，高于双功能催化剂2的31.7kJ/mol。
Trivalent cobalt complexes of salicylaldimine in the presence of an inter- or intramolecular nucleophilic cocatalyst have proven to be excellent catalysts for the copolymerization of CO2 and epoxides to selectively afford the corresponding polycarbonates in perfectly alternating nature. Especially, bifunctional cobalt(III)-salen complexes bearing an appended quaternary ammonium salt are more efficient in catalyzing this copolymerization even at high temperatures and extremely low catalyst loading. The present study focuses on comparative kinetics of two different catalyst systems (binary catalyst system of salen(III)X 1/(Bu4NX)-Bu-n and bifunctional catalyst 2 bearing an appended quaternary ammonium salt, X = 2,4-dinitrophenoxide) for coupling CO2 and epoxides (propylene oxide or cyclohexene oxide) by means of in situ infrared spectroscopy. An induction period was readily found in the binary catalyst system, and its length significantly depends on catalyst loading. Contrarily, no induction period was observed in the bifunctional catalyst 2, in which the overall reaction pathway is consistent with the first-order dependence on catalyst concentration. A reaction order of 1.61 of catalyst concentration was obtained from the binary 1/(Bu4NX)-Bu-n catalyst system, indicating the complexity of the copolymerization. The energies of activation determined for cyclic carbonate and copolymer formation in the coupling reaction of CO2 and propylene oxide catalyzed by the binary 1/(Bu4NX)-Bu-n system are 50.1 and 33.8 kJ/mol, respectively, compared to the corresponding values in the bifunctional catalyst 2 of 77.0 and 29.5 kJ/mol. The big difference in the energies of activation for cyclic carbonate versus copolymer formation accounts for the excellent selectivity for copolymer formation in the bifunctional catalyst systems even at elevated temperatures. In the coupling system of CO2 and cyclohexene oxide, the energy of activation for copolymer (E-a) formation is 47.9 kJ/mol for the binary 1/(Bu4NX)-Bu-n catalyst system, higher than 31.7 kJ/mol determined in the bifunctional catalyst 2.