Atmospheric-Pressure Conversion of CO<sub>2</sub> to Cyclic Carbonates over Constrained Dinuclear Iron Catalysts
Sreenath Pappuru, Dina Shpasser, Raanan Carmieli, Pini Shekhter, Friederike C. Jentoft, Oz M. Gazit
Abstract
High Resolution Image Download MS PowerPoint Slide The conversion of CO 2 and epoxides to cyclic carbonates over a silica-supported di-iron(III) complex having a reduced Robson macrocycle ligand system is shown to proceed at 1 atm and 80 °C, exclusively producing the cis -cyclohexene carbonate from cyclohexene oxide. We examine the effect of immobilization configuration to show that the complex grafted in a semirigid configuration catalytically outperforms the rigid, flexible configurations and even the homogeneous counterparts. Using the semirigid catalyst, we are able to obtain a TON of up to 800 and a TOF of up to 37 h –1 under 1 atm CO 2 . The catalyst is shown to be recyclable with only minor leaching and no change to product selectivity. We further examine a range of epoxides with varying electron-withdrawing/donating properties. This work highlights the benefit arising from the constraining effect of a solid surface, akin to the role of hydrogen bonds in enzyme catalysts, and the importance of correctly balancing it.