Mn^III Porphyrins: Catalytic Coupling of Epoxides with CO₂ under Mild Conditions and Mechanistic Considerations

Abstract

A series of 5,10,15,20‐tetrakis(2,3‐dichlorophenyl)porphyrinate complexes of manganese(III) [MnIII(T2,3DCPP)X] with six different axial ligands (X=NO3−, AcO−, IO3−, Br−, Cl−, HO−) were investigated as catalysts in the cycloaddition reactions of CO2 and styrene oxide (SO), under mild conditions, i. e., atmospheric pressure and 60 °C. [MnIIIT(2,3DCPP)IO3] showed the best catalytic performance, selectively producing the respective cyclic carbonate from diverse epoxides using tetrabutylammonium bromide as a nucleophile source. Mechanistic considerations were inferred from electronic spectra and spectrophotometric titrations, showing that there are a series of equilibriums involved in the formation of the catalytic active species. Stability constants for the proposed equilibrium models were determined using SQUAD software. A catalytic cycle has been proposed based on those observations.

Cycloaddition Reactions of Epoxides and CO2 by the Novel Imidazolium‐Functionalized Metalloporphyrins: Optimization and Analysis using Response Surface Methodology

“…The resulting cyclic carbonates are widely used as intermediates, aprotic polar solvents, electrolytes in lithium ion batteries, raw materials, and fuel additives etc . Recent communications show that metalloporphyrins work cooperatively with quaternary ammonium salts for the cycloaddition of epoxides and CO 2 to produce cyclic carbonates . In particular, the ammonium‐functionalized metalloporphyrins with suitable anions have attracted growing attention.…”

A flexible bis‐Co(III) porphyrin cage as a bimetallic catalyst for the conversion of CO2 and epoxides into cyclic carbonates

“…The bimetallic Co(III) porphyrin cage offers several interesting features regarding such mechanism. Different hexacoordinated Co(III)Cl porphyrins with pyridine and epoxide as axial ligands can be involved in this reaction [18f,22b,27] and the distance between the two metal centres can be adjusted due to the flexible linkers [19,28] . For the epoxide ring‐opening step, a cooperative action of the two catalytic sites in which one axial chloride ligand promotes intramolecular ring opening of the epoxide bound to the other Co(III) site could account for the increased catalytic activity [29] .…”

Metal and Co‐Catalyst Free CO2 Conversion with a Bifunctional Covalent Organic Framework (COF)

“…So far, various catalytic systems, both homogeneous and heterogeneous with different compositions, have been explored for CO 2 cycloaddition reaction. [10][11][12][13][14][15][16] However, they always need a large amount of cocatalyst as well as high reaction temperature and CO 2 pressure, which complicate the separated and synthetic processes with extra cost and environment pollution. [17,18] Thus, it is in urgent need to rationally construct high-efficient and genuine heterogeneous catalytic systems for CO 2 conversion.…”

“…Nevertheless, the CO 2 conversion usually requires strict reaction conditions due to the thermodynamically stable and inert nature of CO 2 . So far, various catalytic systems, both homogeneous and heterogeneous with different compositions, have been explored for CO 2 cycloaddition reaction . However, they always need a large amount of co‐catalyst as well as high reaction temperature and CO 2 pressure, which complicate the separated and synthetic processes with extra cost and environment pollution .…”