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 icat/ip = 303 (icat is the catalytic current, ip 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.