Ya Du

Bifunctional metal-salen complexes as efficient catalysts for the fixation of CO2 with epoxides under solvent-free conditions.

A bifunctional cobalt-salen complex containing a Lewis acidic metal center and a quaternary phosphonium salt unit anchored on the ligand effectively catalyzes the synthesis of cyclic carbonates from CO2 and epoxides under mild conditions without the utilization of additional organic solvents or co-catalysts. The effects of various reaction variables on the catalytic performance were studied in detail and indicate an optimized reaction temperature of about I00 degrees C and CO2 pressure of around 4 MPa, although the reaction proceeds smoothly even at pressures as low as 2 MPa. The catalyst is applicable to a variety of epoxides, producing the corresponding cyclic carbonates in good yields in most cases. Furthermore, the catalyst can be easily recovered and reused several times without significant loss of its catalytic activity. This process thus represents a greener pathway for the environmentally benign chemical fixation of CO2 to produce cyclic carbonates.

Quaternary Ammonium Bromide Functionalized Polyethylene Glycol : A Highly Efficient and Recyclable Catalyst for Selective Synthesis of 5-Aryl-2-oxazolidinones from Carbon Dioxide and Aziridines Under Solvent-Free Conditions

A quaternary ammonium bromide covalently bound to polyethylene glycol (PEG, MW = 6000), i.e., PEG(6000-)(NBu(3)Br)2, was found to be an efficient and recyclable catalyst for the cycloaddition reaction of aziridines to CO(2) under mild conditions without utilization of additional organic solvents or cocatalysts. As a result, 5-aryl-2-oxazolidinone was obtained in high yield with excellent regioselectivity. The catalyst worked well for a wide variety of 1-alkyl-2-arylaziridines. Besides, the catalyst could be recovered by centrifugation and reused without significant loss of catalytic activity and selectivity.

Efficient synthesis of dimethyl carbonate from methanol, propylene oxide and CO2 catalyzed by recyclable inorganic base/phosphonium halide-functionalized polyethylene glycol

The cycloaddition of propylene oxide and CO2 to form propylene carbonate promoted by a phosphonium salt covalently bound to polyethylene glycol (PEG), and the transesterification of propylene carbonate with methanol to dimethyl carbonate (DMC) mediated by PEG-supported K2CO3, were separately investigated. Inorganic base/phosphonium halide-functionalized PEG (K2CO3/BrBu3PPEG6000PBu3Br) was shown to be active for DMC synthesis from propylene oxide, CO2 and methanol under mild reaction conditions, even under low CO2 pressure (2 bar). The effects of various reaction variables on the activity and selectivity performance are discussed in detail. The catalyst was readily separated and reused, without catalyst leaching being detected by 31P NMR. Notably, excellent yields of DMC and complete conversion of propylene carbonate were reached under the optimized reaction conditions. This procedure was successfully applied to the synthesis of other dialkyl carbonates.

Environmentally Benign Chemical Conversion of CO2 into Organic Carbonates Catalyzed by Phosphonium Salts

Quaternary phosphonium salts were proved efficient homogeneous catalysts for solvent-free synthesis of cyclic carbonates from carbon dioxide and epoxides. Propylene carbonate was produced in quantitative yield and excellent selectivity. Furthermore, a PEG-supported phosphonium salt was solidified by adding ether and cooling after reaction and recovered by a simple filtration. Hence immobilization of a phosphonium salt on PEG provides an alternative pathway for realizing homogeneous catalyst recycling.