Darensbourg Donald J, Yarbrough Jason C, Ortiz Cesar, Fang Cindy C
Department of Chemistry, Texas A&M University, College Station, TX 77843, USA.
J Am Chem Soc. 2003 Jun 25;125(25):7586-91. doi: 10.1021/ja034863e.
The catalysis of the reaction of carbon dioxide with epoxides (cyclohexene oxide or propylene oxide) using the (salen)Cr(III)Cl complex as catalyst, where H(2)salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexenediimine (1), to provide copolymer and cyclic carbonate has been investigated by in situ infrared spectroscopy. As previously demonstrated for the cyclohexene oxide/CO(2) reaction in the presence of complex 1, coupling of propylene oxide and carbon dioxide was found to occur by way of a pathway first-order in catalyst concentration. Unlike the cyclohexene oxide/carbon dioxide reaction catalyzed by complex 1, which affords completely alternating copolymer and only small quantities of trans-cyclic cyclohexyl carbonate, under similar conditions propylene oxide/carbon dioxide produces mostly cyclic propylene carbonate. Comparative kinetic measurements were performed as a function of reaction temperature to assess the activation barrier for production of cyclic carbonates and polycarbonates for the two different classes of epoxides, i.e., alicyclic (cyclohexene oxide) and aliphatic (propylene oxide). As anticipated in both instances the unimolecular pathway for cyclic carbonate formation has a larger energy of activation than the bimolecular enchainment pathway. That is, the energies of activation determined for cyclic propylene carbonate and poly(propylene carbonate) formation were 100.5 and 67.6 kJ.mol(-1), respectively, compared to the corresponding values for cyclic cyclohexyl carbonate and poly(cyclohexylene carbonate) production of 133 and 46.9 kJ.mol(-1). The small energy difference in the two concurrent reactions for the propylene oxide/CO(2) process (33 kJ.mol(-1)) accounts for the large quantity of cyclic carbonate produced at elevated temperatures in this instance.
以（salen）Cr（III）Cl配合物为催化剂，其中H(2)salen = N,N'-双（3,5-二叔丁基水杨醛）-1,2-环己二亚胺（1），通过原位红外光谱研究了其催化二氧化碳与环氧化物（环氧环己烷或环氧丙烷）反应以生成共聚物和环状碳酸酯的过程。如之前在配合物1存在下环氧环己烷/CO(2)反应所证明的那样，发现环氧丙烷与二氧化碳的偶联通过一条对催化剂浓度呈一级反应的途径发生。与配合物1催化的环氧环己烷/二氧化碳反应不同，该反应生成完全交替的共聚物且仅产生少量反式环状碳酸环己酯，在相似条件下环氧丙烷/二氧化碳反应主要生成环状碳酸丙烯酯。进行了作为反应温度函数的比较动力学测量，以评估两种不同类型环氧化物，即脂环族（环氧环己烷）和脂肪族（环氧丙烷）生成环状碳酸酯和聚碳酸酯的活化能垒。在这两种情况下，正如预期的那样，环状碳酸酯形成的单分子途径比双分子链增长途径具有更高的活化能。也就是说，测定的环状碳酸丙烯酯和聚（碳酸丙烯酯）形成的活化能分别为100.5和67.6 kJ·mol(-1)，而环状碳酸环己酯和聚（碳酸环己酯）生成的相应值为133和46.9 kJ·mol(-1)。环氧丙烷/CO(2)过程中两个并行反应的小能量差（33 kJ·mol(-1)）解释了在此情况下高温下产生大量环状碳酸酯的原因。
