Figure 5. H₂ production catalytic cycle of L^N2S2Ni^IIFe^II.

Proposed catalytic pathway for H₂ evolution mediated by L^N2S2Ni^IIFe^II at the catalytic wave. After a one-electron reduction, L^N2S2Ni^IIFe^II generates L^N2S2Ni^IFe^II, a mimic of the Ni-L state, which is then further reduced to afford the metal-radical complex L^N2S2•Ni^IFe^II. The latter reacts with protons to yield the metal-hydride complex L^N2S2Ni^II(H)Fe^II, a model of Ni-R, which is protonated to produce H₂ with concomitant regeneration of the initial L^N2S2Ni^IIFe^II complex.