A homogenous binary catalyst system, n-Bu4NBr/n-Bu3N, was found to be active for the synthesis of dimethyl carbonate from styrene oxide (SO), methanol, and supercritical CO2. Under the optimized conditions, the dimethyl carbonate yield could reach 84% at SO conversion of 98%. Several parameters were studied, i.e. catalyst precursors, reaction time and temperature, methanol/epoxide feed ratio in moles, and CO2 pressure. The best compromise for the one-pot synthesis was achieved with an equimolar amount of n-Bu4NBr/n-Bu3N. A possible mechanism for the present n-Bu4NBr/n-Bu3N-catalyzed one-pot synthesis of dimethyl carbonate was proposed.

Tetraalkylammonium salts of transition-metal-substituted polyoxometalates, such as [(n-C7H15)4N]6[α-SiW11O39Co] and [(n-C7H15)4N]6[α-SiW11O39Mn], efficiently catalyze cyclic carbonate synthesis from carbon dioxide and epoxide. The catalytic activity is significantly influenced by the type of transition metal and the countercation (Co2+≈Mn2+>Ni2+>Fe3+»Cu2+; (n-C7H15) 4N+>(n-C4H9)4N+»K+). Co- or Mn-substituted catalysts required neither additional organic solvents nor additives. Thus, polyoxometalates are promising as nonhalogen anionic components of catalysts for cyclic carbonate synthesis.

Insoluble ion exchange resins, one type of polystyryl supported catalysts containing an ammonium salt or amino group, and the polar macroporous adsorption resin, are efficient and reusable heterogeneous basic catalysts for the synthesis of propylene carbonate from propylene oxide and CO2 under supercritical CO2 conditions (373K, 8MPa), which requires no additional organic solvents either for the reaction or for the separation of product. Various parameters affecting the reaction were examined. A quantitative yield (>99%) together with excellent selectivity (>99%) was obtained. The purity of product separated directly by filtration from the reaction mixture, reached more than 99.3% without further purification processes. The catalyst can be easily recovered and reused without significant loss of its catalytic activity. The process represents a simple, ecologically safer, cost-effective route to cyclic carbonates with high product quality, as well as easy product recovery and catalyst recycling.

Ruthenium and rhodium phosphine complexes catalyze the hydrosilation of olefins in dense carbon dioxide. The incorporation of polyfluorinated phosphine ligands in the conventional hydrosilation catalysts provides enhanced solubility in dense carbon dioxide resulting in a higher catalytic activity and selectivity; the best result was obtained using RuCl2[P(C6H4-p-CF3)3]3. The reaction is applicable to the synthesis of a fluorous silane coupling agent.

Polyfluoroalkyl phosphonium iodides, Rf3RPI (Rf=C4F9C2H4, C6F13C2H4, C8F17C2H4; R=Me, Rf), catalyzed propylene carbonate synthesis from propylene oxide and carbon dioxide under supercritical CO2 conditions, where propylene carbonate was spontaneously separated out of the supercritical CO2 phase. The Rf3RPI catalyst could be recycled with maintaining a high CO2 pressure and temperature by separating the propylene carbonate from the bottom of the reactor followed by supplying propylene oxide and CO2 to the upper supercritical CO2 phase in which the Rf3RPI remained.