To curtail the accumulation of CO₂ concentration in the atmosphere, different strategies have been adopted at present. Among them, one of the possible methods of reducing CO₂ level involves transforming it into useful organic compounds. In this line, converting CO₂ to cyclic carbonates is a topic of interest as cyclic carbonates are commercially important chemicals. Recently, Honores and co-workers have experimentally prepared cyclic carbonates from cycloaddition of CO₂ and ethylene oxide/propylene oxide/Epichlorohydrin catalyzed by Co-ethylenediamine (en) complexes using [BMIm][BF₄] ionic liquid as solvent. This work explores the complete reaction mechanism of the cycloaddition reaction at B3LYP/LANL2DZ(6−31G*) level of density functional theory. Two mechanist routes were computed: first route deals with the reaction mechanism without the presence of ionic liquid and second route deals with the ionic liquid involved reaction mechanism. In both the routes, the ring closure step was calculated to be the rate-determining step with an activation barrier in the range of 47.87–52.23 kcal/mol in the absence of ionic liquid and 48.82 to 35.29 kcal/mol in the presence of ionic liquid. Interestingly, the involvement of ionic liquids in the reaction mechanism was found to remarkably reduce the activation free energy barriers by 2.12–19.31 kcal/mol in all the steps along the proposed mechanism. Geometrical analysis indicated that the ability of ionic liquids to form intermolecular hydrogen bonding interaction with the catalyst and substrate is the reason behind the decrease in the barriers. In order to quantify the strength of the hydrogen bonding interactions, NBO analysis was performed on key transition state geometries and n_B-F → σ*_H-N hydrogen bonding interactions between anionic part of IL and en ligand framework were found to possess significant second-order stabilization energies. Overall, this study sheds light on the mechanistic details of the cycloaddition reaction of CO₂ and epoxide and also substantiates that the ionic liquids are efficient green solvents which can be employed in similar catalytic reactions to achieve more efficiency.

为了减少大气中CO ₂浓度的积累，目前已经采用了不同的策略。其中，降低CO ₂水平的一种可能方法是将其转化为有用的有机化合物。在这条生产线中，将 CO ₂转化为环状碳酸酯是一个令人感兴趣的话题，因为环状碳酸酯是商业上重要的化学品。最近，Honores 及其同事使用 [BMIm][BF ₄由 Co-乙二胺 (en) 配合物催化CO ₂和环氧乙烷/环氧丙烷/环氧氯丙烷的环加成反应实验制备了环状碳酸酯。] 离子液体作溶剂。本工作在密度泛函理论的 B3LYP/LANL2DZ(6−31G*) 水平上探索了环加成反应的完整反应机理。计算了两条机理路线：第一条路线处理不存在离子液体的反应机理，第二条路线处理涉及离子液体的反应机理。在这两种路线中，闭环步骤被计算为速率决定步骤，在不存在离子液体的情况下活化势垒范围为 47.87-52.23 kcal/mol，在离子液体存在下为 48.82 至 35.29 kcal/mol液体。有趣的是，离子液体参与反应机理被发现在沿所提出机理的所有步骤中将活化自由能垒显着降低了 2.12-19.31 kcal/mol。几何分析表明，离子液体与催化剂和底物形成分子间氢键相互作用的能力是势垒降低的原因。为了量化氢键相互作用的强度，对关键的过渡态几何形状和 n 进行了 NBO 分析。_{发现 BF} → σ* _HN在 IL 的阴离子部分和 en 配体框架之间的氢键相互作用具有显着的二级稳定能。总体而言，这项研究揭示了 CO ₂和环氧化物的环加成反应的机理细节，并证实了离子液体是高效的绿色溶剂，可用于类似的催化反应以实现更高的效率。