A Mn(II)-porphyrin based metal-organic framework (MOF) for visible-light-assisted cycloaddition of carbon dioxide with epoxides

The construction of a microporous 3D supramolecular Mn(II)-porphyrin metal-organic framework, [{Mn(TCPP)0.5(H2O)2}.2H2O]n (MOF1) (where, TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) exhibiting unprecedented visible-light-assisted cycloaddition of CO2 with epoxides to generate cyclic carbonates at mild conditions of room temperature (RT) and 1 bar CO2 has been reported. Single crystal structure determination reveals that MOF1 has an interesting microporous 2D network structure with 1D channels of dimension, 6.32 × 11.88 Å2 along the crystallographic c-axis. The 2D networks are further interacting through O-H⋯O hydrogen bonding interaction between carboxylate oxygen and hydrogen of water molecules coordinated to Mn(II) center forming a 3D supramolecular framework. Gas adsorption studies revealed selective adsorption property of MOF1 for CO2 (selectivity constants for CO2/H2 = 39, CO2/N2 = 19, CO2/Ar = 21) with the isosteric heat of adsorption value of 32.9 kJ/mol. Further, MOF1 acts as an efficient recyclable heterogeneous catalyst for cycloaddition of CO2 with epoxides to generate cyclic carbonates with high selectivity and yield at mild conditions of RT and 1 bar of CO2. More interestingly, the rate of catalytic conversion of CO2 was enhanced with irradiation of visible light owing to good visible light absorption property of the porphyrin linker. The enhanced catalytic activity of MOF1 under the irradiation of visible-light has been attributed to the in situ generation of thermal energy by photo-thermal effect. Therefore, herein, for the first time, visible-light-assisted efficient cycloaddition of CO2 with epoxides catalyzed by a Mn(II)-porphyrin MOF has been reported.