Coupling Reactions of CO2 and Epoxides

Another important transformation is the coupling of COj and epoxides. The coupling reactions ofCOj and epoxides generate cyclic carbonates or polycarbonates, which are important chemical products in industry [17]. Thus far, there are a number of theoretical studies on the mechanism of these coupling reactions catalyzed by transition metal complexes [18]. 

It is now well estabUshed that the mechanism of the transition metal-catalyzed coupling reactions of CO, and epoxides includes three main steps, epoxides oxidative addition, CO2 insertion, and reductive elimination of carbonates. The important issue of the mechanism is whether first to activate the epoxides or C02- In the following paragraphs, we will discuss a couple of examples to illustrate the mechanistic details. 

Experimentally, Pasquale found that Ni(PPh3)2 is a good catalyst for the coupling reaction between CO2 and epoxyethane [19]. Control experiments 

Summarizing the results discussed above, we see that in the Ni(PH3)2-catalyzed coupling reaction of COj and epoxyethane, the epoxide was first oxidatively added to Ni(PH3)2 to form oxametallacyclobutane, followed by CO2 insertion. However, in the (BDI)ZnOMe-catalyzed coupling reaction of CO2 and cyclohexene oxide, CO2 insertion occurs first. These results indicate that CO2 inserts preferentially 

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In this chapter, we have reviewed theoretical studies of selected transition metal-catalyzed transformation of CO2 (i) hydrogenation of CO2 with H2 (ii) coupling reactions of CO2 and epoxides (iii) reduction of CO2 with organoborons (iv) carboxylation of olefins with CO2 and (v) hydrocarboxylation of olefins with CO ... 

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