Photocatalytic reductive carboxylation of terminal alkynes with CO2 using heterostructured ZIF-7/BiOBr under visible-light illumination

Abstract

Carboxylation of the organic compounds utilizing CO2 is a challenging task because of the higher thermodynamic stability and chemical inertness of the CO2 molecule. In the present study a straight protocol for the reductive carboxylation of terminal alkynes with CO2 has been developed, providing regioselective synthesis of α, β-unsaturated carboxylic acids using a heterostructured photocatalyst composed of Zn-benzimidazolate framework (ZIF-7) and BiOBr without any additional reducing agent at room temperature and atmospheric pressure conditions. The electron rich derivatives of phenyl acetylene substrates afforded α-acids; whereas, electron deficient substrates provided terminal acids. The DFT calculations indicated the type-II band alignment nature of ZIF-7/BiOBr in which electrons migrated from the ZIF to BiOBr and interacted with CO2 to generate CO2 radical anion at the conduction band of BiOBr.