The mechanistic study of CO₂ coupling with propylene oxide (PO) into cyclic carbonate catalyzed by (CH₃)₄PI has been investigated using the B₃LYP/6-311++G (d, p)/B₃LYP/6-31G (d) level of theory for non-iodine atoms and LANL2DZ was used, together with its associated basis set for the iodine atom. Two hypothetical reaction mechanisms were proposed for the studied reaction and thermodynamic and kinetic parameters were computed for each step to determine the more favorable route. The density functional theory (DFT) study reveals that the reaction prefers to proceed through a three-step mechanism (pathway II) than a tri-molecular intermediate (pathway I) where the CO₂ and the catalyst act simultaneously on the PO ring. The rate-determining step of the catalytic reaction is found to be the ring-opening step with an energy barrier of 27.1 kcal/mol (pathway II) in the gas phase, which is kinetically more favorable than that of non-catalytic CO₂ fixation with a relatively higher barrier of 63.7 kcal/mol. The synergetic effect of MgCl₂ is tested as a cocatalyst for the (CH₃)₄PI/MgCl₂ catalyzed reaction and it gave a better result and minimized the activation energy for the reaction and the rate-determining step was the ring closure with the free energy of activation 18.8 kcal/mol in the gas phase. The polarizable continuum model was used to account for the solvent effect, obtaining the best results of 23.1 kcal/mol in water for pathway I and 16.5 kcal/mol and 14.9 kcal/mol in dimethyl sulfoxide for pathway II and binary system, respectively.

中文翻译：

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(CH3)4PI·MgCl2催化CO2与环氧丙烷偶联反应的机理研究

_{使用B 3} LYP/6-311++G (d, p)/B ₃ LYP/6研究了(CH ₃ ) ₄ PI催化CO ₂与环氧丙烷(PO)偶联生成环状碳酸酯的机理。使用了非碘原子和 LANL2DZ 的 -31G (d) 水平理论，以及碘原子的相关基组。为所研究的反应提出了两种假设的反应机制，并为每个步骤计算了热力学和动力学参数以确定更有利的路线。密度泛函理论 (DFT) 研究表明，与 CO ₂并且催化剂同时作用在PO环上。发现催化反应的速率决定步骤是开环步骤，在气相中的能垒为 27.1 kcal/mol（途径 II），这在动力学上比非催化 CO ₂固定更有利具有相对较高的屏障，为 63.7 kcal/mol。_{MgCl 2}的协同效应作为 (CH ₃ ) ₄ PI/MgCl _{2的助催化剂进行了测试}催化反应，它给出了更好的结果，并且最小化了反应的活化能，并且速率决定步骤是在气相中活化自由能为18.8 kcal / mol的环闭合。极化连续介质模型用于解释溶剂效应，在路径 I 的水中获得了 23.1 kcal/mol 的最佳结果，在二甲基亚砜中获得了 16.5 kcal/mol 和 14.9 kcal/mol 的最佳结果，对于路径 II 和二元系统，分别。