(Salen)Co(II)/n-Bu4NX Catalysts for the Coupling of CO2 and Oxetane: Selectivity for Cyclic Carbonate Formation in the Production of Poly(trimethylene carbonate)
(Salen)Co(II)/n-Bu4NX Catalysts for the Coupling of CO2 and Oxetane: Selectivity for Cyclic Carbonate Formation in the Production of Poly(trimethylene carbonate)
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DOI：
10.1021/ma9002006
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发表时间：
2009-06-23
期刊：
影响因子：
5.5
通讯作者：
Moncada, Adriana I.
中科院分区：
文献类型：
--
作者：
Darensbourg, Donald J.;Moncada, Adriana I.
在阴离子引发剂如溴化物的存在下，The(salen)Co(II)complex((1R，2R)-(-)-1，2-cyclohexanediamino-N，N‘-bis(3，5-di-tert-butyl-salicylidene)cobalt(II))已被证明是氧杂环己烷和二氧化碳偶联的非常有效的催化体系，提供相应的聚碳酸酯的醚键最少。用原位红外光谱研究了环氧乙烷与二氧化碳的偶联反应机理，首次生成的产物为碳酸三亚甲酯(TMC)。TMC是在阴离子引发剂将氧杂环己烷开环后，二氧化碳插入钴-氧键后，通过反咬机制形成的。共聚物的形成主要是在溶液中存在阴离子的情况下，通过预制的碳酸三亚甲酯的阴离子开环聚合进行的。好的离开基团的阴离子，即溴化物和碘化物，通过这一路线最有效地提供共聚物。在存在大于2当量的阴离子时，共聚产物的总生成速率降低，可能是由于氧杂环己烷单体与钴中心的结合受到抑制。然而，在这些条件下，通过TMC的ROP形成的共聚物被促进，质谱学证据表明TMC形成了二聚体。
The(salen)Co(II)complex((1R,2R)-(-)-1,2-cyclohexanediamino-N,N'-bis(3,5-di-tert-butyl-salicylidene)cobalt(II)) in the presence of an anion initiator, e.g. bromide, has been shown to be a very effective catalytic system for the coupling of oxetane and carbon dioxide, to provide the corresponding polycarbonate with minimal amount of ether linkages. The mechanism of the coupling of oxetane and carbon dioxide has been studied by in situ infrared spectroscopy, where the first formed product is trimethylene carbonate (TMC). TMC is formed by a backbiting mechanism following ring-opening of oxetane by the anion initiator, subsequent to CO2 insertion into the cobalt-oxygen bond. The formation of the copolymer is shown to proceed mostly by way of the anionic ring-opening polymerization of preformed trimethylene carbonate in the presence of an anion in solution. Anions that are good leaving groups, i.e., bromide and iodide, are most effective at affording copolymer via this route. In the presence of greater than 2 equiv of anions the overall rate of copolymer production is decreased, presumably due to inhibition of oxetane monomer binding to the cobalt center. However, under these conditions copolymer formation through ROP of TMC is enhanced, with mass spectral evidence found for the formation of a dimer of TMC.