Synthesis of cyclic carbonates through cycloaddition of electrocatalytic activated CO2 to epoxides under mild conditions

Abstract

Abstract A nickel complex, 2,4,10,12-tetramethyl-1,5,9,13-(14-nitrobenzo) tetraaza cyclopentadecinato (2-) nickel (II), exhibits an excellent electrocatalytic activity for the reduction of carbon dioxide in a acetonitrile (ACN) solution at room temperature. The results show an increase of the cathodic current, a decrease of the anodic current, and a diminution of the overpotential about 700 mV for reduction of CO2 in the presence of the complex compared to the process at the absence of the complex. The electrocatalytic cycloaddition of carbon dioxide to epoxides catalyzed by nickel (II) complex afforded cyclic carbonates under mild conditions (atmospheric CO2 pressure, room temperature). The mechanism of cycloaddition is initiated by the nucleophilic attack of electrocatalytically generated CO2 on epoxide. Then, a cyclic carbonate product is produced through the oxidation of the intermediate by the nickel (II) complex. To support this hypothesis, we have calculated the electrode potential and thermodynamic parameters of the cyclic carbonate product (propylene carbonate) theoretically using accurate ab initio calculations along with the available solvation model. Also, the redox potential of the Ni (II) complex was determined by cyclic voltammetry using a bare glassy carbon electrode (GCE) in acetonitrile/TBAP supporting electrolyte. A comparison of the redox potentials of the Ni (II) complex and the cyclic carbonate confirms the proposed mechanism.