𝛽-Tetrathiocyano Cobalt(III) Corroles as Redox-Tunable Molecular Catalysts for Hydrogen Evolution

The development of efficient molecular catalysts based on earth-abundant metals is essential for sustainable hydrogen production. Here, we report two new 𝛽-tetrathiocyano cobalt(III) corrole complexes bearing axial pyridine ligands, designed to examine the influence of strongly electron-withdrawing thiocyanate substituents on the electronic structure and catalytic activity of cobalt corroles toward the hydrogen evolution reaction (HER). Spectroscopic characterization together with SC-XRD reveals a distorted octahedral coordination environment around the cobalt center and a significantly saddle-distorted corrole macrocycle. Electronic absorption spectroscopy and TD-DFT calculations show that the frontier orbitals are predominantly ligand-centered, consistent with an electronically innocent Co(III) ground state. Electrochemical studies reveal two sequential reduction processes leading to catalytically relevant low-valent cobalt intermediates. In the presence of trifluoroacetic acid, pronounced catalytic current enhancement is observed, indicating efficient proton reduction. Controlled-potential electrolysis combined with gas chromatography confirms sustained hydrogen evolution with a turnover frequency of 2.66 s -1 . Post-electrolysis spectroscopic analyses show minimal changes in the corrole framework, supporting a homogeneous catalytic process. Free-energy calculations further support a catalytic pathway involving sequential electron accumulation, cobalt hydride formation, and subsequent H 2 release. These results demonstrate that 𝛽-thiocyanate substitution effectively tunes the redox properties of cobalt corroles and promotes proton-coupled electron transfer, providing a useful strategy for designing efficient molecular HER catalysts based on earth-abundant metals.