Mechanism of fixation of CO2 with an epoxide catalyzed by ZnBr2 and a choline chloride co-catalyst: a DFT study

摘要

To explore the reason for the high activity of the cycloaddition reaction of PO (propylene oxide) with CO2 catalyzed by ZnBr2/CH (choline chloride) co-catalyst, the mechanism has been constructed using a DFT (density functional theory) method. The combination of CH and ZnBr2 will generate three new stable complexes, i.e., [Ch](2)[ZnBr2Cl2], Ch(+)ZnBr(2)Cl(-), and Ch(+)ZnBrCl(2)(-). The latter two are derived from the dissociation of [Ch](2)[ZnBr2Cl2]. The detailed mechanism of a coupling reaction catalyzed by the more stable complex Ch(+)ZnBrCl(2)(-) is explored. It has been elucidated that the attack from the Zn complex and the Br- anion is the major factor in promoting the cleavage of the C-O bond of PO. Finally, the performance of [Ch](2)[ZnBr2Cl2] is also investigated, providing less activity, indicating that it should dissociate to gain better catalytic effect.