Highly active Mn(III) meso-tetrakis(2,3-dichlorophenyl)porphyrin catalysts for the cycloaddition of CO2 with epoxides

• Published in: Journal of CO2 utilization 2019-03, Vol.30, p.100-106
• Main Authors: Milani, Jorge Luiz Sônego, Meireles, Alexandre Moreira, Cabral, Bruno Noschang, de Almeida Bezerra, Werberson, Martins, Felipe Terra, da Silva Martins, Dayse Carvalho, das Chagas, Rafael Pavão
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Cyclic carbonate; Homogeneous catalysis; Manganese complexes; Metalloporphyrins
• ISSN: 2212-9820; 2212-9839
• DOI: 10.1016/j.jcou.2018.12.017

•New class of MnIII-porphyrin catalysts.•Highly active catalytic system for the cycloaddition reaction of CO2 with epoxides.•Excellent conversions, TONs and TOFs in the synthesis of cyclic carbonates.•Recyclable catalytic system. A new free-base porphyrin, meso-tetrakis(2,3-dichlorophenyl)porphyrin, (H2T2,3-DCPP) and the respective manganese(III) complexes [MnIII(T2,3-DCPP)X] with six different axial ligands (NO3−, AcO−, IO3−, Br−, Cl−, HO−) were synthesized and characterized. The molecular structure of [MnIII(T2,3-DCPP)Cl] was also confirmed by single crystal X-ray diffraction. The complexes, when combined with tetrabutylammonium halides as nucleophile source cocatalysts, were highly active catalysts in the solvent-free cycloaddition reactions of carbon dioxide with styrene oxide, selectively producing the respective cyclic carbonate. The complex [MnIII(T2,3-DCPP)Cl] was used to evaluate a series of parameters in the system and efficiently catalyzed the transformation of various epoxides using TBAI as cocatalyst, 30 bar of CO2 at 100 °C, producing nearly quantitative conversions in most of the cases. Remarkable TON values of 500,000 and 434,780 were achieved, respectively, for propylene oxide and styrene oxide using [MnIII(T2,3-DCPP)Cl] as catalyst. Recycling experiments were conducted and the system maintains high conversion rates after eight runs, which indicated a high stability and reusability of the catalyst.