Homogeneous Catalysis Promoted by Carbon Dioxide

Supercritical CO2 (scCO2), which is recognized as CO2 heated and pressurized beyond its critical point (T c = 31.06 °C, P c = 7.38 MPa), is considered to be a suitable candidate for the replacement of conventional organic solvents, owing to its unique physical properties, such as abundantly available and cheap, nontoxic and environmentally benign, nonflammable and nonreactive even under oxidative conditions, high gaseous miscibility, effective mass transfer, easily tunable properties with subtle variation of pressure or temperature, weakening of the solvent interactions around the reacting species, and easy separation and recycling. In particular, smart use of dense CO2 would pronouncedly enhance the selectivity of target products and improve catalytic efficiency and lifetime of the catalyst. In this chapter, utilization of scCO2 as innovative and environmentally friendly reaction medium for chemical syntheses and especially for the metal-catalyzed reactions, including hydrogenation (asymmetric hydrogenation, hydrogenation, and hydroboration of styrene), carbonylation (hydroformylation, hydroesterification), C–C forming reaction (Diels–Alder cycloaddition, coupling reaction, olefin metathesis, Aldol reaction, miscellaneous reactions), oxidation reaction (oxidation reaction of alcohols, aldehydes, hydrocarbon and olefins, Baeyer–Villiger reaction), and polymerization (free radical polymerization, cationic polymerization, metal-catalyzed polymerization) is summarized.