Reactivity and Mechanism Studies of Hydrogen Evolution Catalyzed by Copper Corroles

Several copper corrole complexes were synthesized, and their catalytic activities for hydrogen (H₂) evolution were examined. Our results showed that substituents at the meso positions of corrole macrocycles played significant roles in regulating the redox and thus the catalytic properties of copper corrole complexes: strong electron-withdrawing substituents can improve the catalysis for hydrogen evolution, while electron-donating substituents are not favored in this system. The copper complex of 5,15-pentafluorophenyl-10-(4-nitrophenyl)­corrole (1) was shown to have the best electrocatalytic performance among copper corroles examined. Complex 1 can electrocatalyze H₂ evolution using trifluoroacetic acid (TFA) as the proton source in acetonitrile. In cyclic voltammetry, the value of i_cat/i_p = 303 (i_cat is the catalytic current, i_p is the one-electron peak current of 1 in the absence of acid) at a scan rate of 100 mV s^–1 and 20 °C is remarkable. Electrochemical and spectroscopic measurements revealed that 1 has the desired stability in concentrated TFA acid solution and is unchanged by functioning as an electrocatalyst. Stopped-flow, spectroelectrochemistry, and theoretical studies provided valuable insights into the mechanism of hydrogen evolution mediated by 1. Doubly reduced 1 is the catalytic active species that reacts with a proton to give the hydride intermediate for subsequent generation of H₂.