Transition Metal-Promoted Carboxylation of Unsaturated Compounds with CO2

Carbon dioxide (CO2), a resourceful, renewable, and non-toxic C1 resource, is of great significance if applied to produce value-added chemicals. In recent years, CO2 valorization has been well exploited as expected. Among them, functionalizing organic substrates with CO2 to synthesize high value-added carboxylic acid compounds is extremely attractive. Since carboxylic acids and its derivatives are essential structural motifs in pharmaceuticals, pesticides, fine chemicals, commodities, and natural products. Moreover, dicarboxylic acids are very appealing monomers for the manufacture of functional plastics and rubbers. Therefore, considerable efforts have been devoted to developing synthetic methods of carboxylic acids and expanding their applications. Notably, carboxylation reactions of unsaturated organic compounds (e.g., alkenes, alkynes, aromatic hydrocarbons) with CO2 catalyzed by transition metals have been regarded as an efficacious way to synthesize diverse functionalized carboxylic acids and its derivatives. In this chapter, we summarize the advancement of carboxylation reactions of unsaturated compounds such as (1) carboxylation of C–H bond, (2) heterocarboxylation, (3) hydrocarboxylation, and (4) dicarboxylation, promoted by transition metal complexes such as Ni, Cu, Pd, Au, Rh, and so on. We are focusing on their rationales behind and several kinds of important products which include aryl carboxylic acid, α, β-unsaturated carboxylic acid, functionalized carboxylic acid, and dicarboxylic acid.