Hydrogen evolution catalysis by terminal molybdenum-oxo complexes

Stable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons to hydrogen gas. The upto 670 mV differences in the [(oxo)Mo(IV)]/[(oxo)Mo(III)](-2) redox potentials of the dissolved complexes came into effect by the catalytic onset potential for proton reduction thereby, significantly earlier than their reduction process in the absence of acids, but the two more promising complexes were not stable at practical conditions. Under heterogeneous conditions, the smallest and most electron-withdrawing catalyst did excel by all relevant criteria, including a 97% Faradaic efficiency for catalyzing HER from acidic water. This suggests complexes based on molybdenum, the only sustainable heavy transition metal, as catalysts for other yet unexplored green-energy-relevant processes.

Automated summary

This study reports the preparation of three conceptually different (oxo)molybdenum(V) corroles to test if proton-assisted 2-electron reduction leads to hyper-reactive molybdenum(III) catalysts capable of converting protons to hydrogen gas. The most electron-withdrawing catalyst showed excellent performance in catalyzing the HER from acidic water with a 97% Faradaic efficiency, suggesting molybdenum-based complexes as promising catalysts for other green-energy-relevant processes.