Bifunctional Metal‐Salen Complexes as Efficient Catalysts for the Fixation of CO₂ with Epoxides under Solvent‐Free Conditions

Abstract

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.

Guanidine Hydrochloride/ZnI2 as Heterogeneous Catalyst for Conversion of CO2 and Epoxides to Cyclic Carbonates under Mild Conditions

“…The desired product yield was obtained even at low CO2 pressure of 1.0 MPa over GndCl/ZnI2 catalysts. A similar effect of CO2 pressure on catalytic activity was observed in other catalytic systems [6,[25][26][27], which could be explained by the fact that the introduced CO2 was dissolved in propylene oxide or "liquefied" by the formation of a CO2-PO complex [23]. In the low-pressure range, increasing CO2 pressure led to an increase of CO2-PO concentration in the liquid phase and thus enhanced the PC yield.…”

Multinuclear Cu(II) Schiff Base Complex as Efficient Catalyst for the Chemical Coupling of CO2 and Epoxides: Synthesis, X-ray Structural Characterization and Catalytic Activity

“…CO 2 is a particularly attractive alternative feedstock as it is inexpensive, highly naturally abundant, and the byproduct of many industrial processes, including combustion [1]. The reactions of CO 2 with metal complexes has been extensively studied, revealing potential pathways for catalytic reactions [2][3][4][5]. However the thermodynamic stability of CO 2 has hampered its utility as a reagent for chemical synthesis; in fact its high stability makes it an ideal medium for many chemical processes [2,6].…”

Coupling of carbon dioxide with neat propylene oxide catalyzed by aminebisphenolato cobalt(II)/(III) complexes and ionic co-catalysts

“…Subsequently, it was shown that in these examples the phenolic ligands themselves could perform such reactions and similar TONs could be obtained without the need for a metal [11]. A range of bifunctional cobalt-salen complexes have been reported that under the appropriate conditions either copolymerize or form cyclic carbonates from propylene oxide and carbon dioxide [12][13][14][15]. We have recently reported a series of well-characterized Co(II) complexes [16].…”