Electron transfer and hydrogen generation from a molecular dyad: platinum(II) alkynyl complex anchored to [FeFe] hydrogenase subsite mimic

A PS-Fe2S2 molecular dyad 1a directly anchoring a platinum(II) alkynyl complex to a Fe2S2 active site of a [FeFe] H(2)ase mimic, and an intermolecular system of its reference complexes 1b and 2, have been successfully constructed. Time-dependence of H-2 evolution shows that PS-Fe2S2 1a as well as complex 2 with 1b can produce H-2 in the presence of a proton source and sacrificial donor under visible light irradiation. Spectroscopic and electrochemical studies on the electron transfer event reveal that the reduced (FeFe0)-Fe-I species generated by the first electron transfer from the excited platinum(II) complex to the Fe2S2 active site in PS-Fe2S2 1a and complex 2 with 1b is essential for photochemical H-2 evolution, while the second electron transfer from the excited platinum(II) complex to the protonated (FeFe0)-Fe-I species is thermodynamically unfeasible, which might be an obstacle for the relatively small amount of H-2 obtained by PS-Fe2S2 molecular dyads reported so far.