Photocatalytic Hydrogen Generation by Vesicle-Embedded [FeFe]Hydrogenase Mimics: A Mechanistic Study

Artificial photosynthesis—the direct photochemical generation of hydrogen from water—is a promising but scientifically challenging future technology. Because nature employs membranes for photodriven reactions, the aim of this work is to elucidate the effect of membranes on artificial photocatalysis. To do so, a combination of electrochemistry, photocatalysis, and time‐resolved spectroscopy on vesicle‐embedded [FeFe]hydrogenase mimics, driven by a ruthenium tris‐2,2′‐bipyridine photosensitizer, is reported. The membrane effects encountered can be summarized as follows: the presence of vesicles steers the reactivity of the [FeFe]‐benzodithiolate catalyst towards disproportionation, instead of protonation, due to membrane characteristics, such as providing a constant local effective pH, and concentrating and organizing species inside the membrane. The maximum turnover number is limited by photodegradation of the resting state in the catalytic cycle. Understanding these fundamental productive and destructive pathways in complex photochemical systems allows progress towards the development of efficient artificial leaves

[FeFe]‐Hydrogenase Mimic Employing κ²‐<i>C,N</i>‐Pyridine Bridgehead Catalyzes Proton Reduction at Mild Overpotential

Two novel κ2‐C,N‐pyridine bridged [FeFe]‐H2ase mimics ( 1 and 2 ) have been prepared and are shown to function as efficient molecular catalysts for electrocatalytic proton reduction. The elemental and structural composition of the complexes are confirmed by NMR and IR spectroscopy, high‐resolution mass spectrometry and single‐crystal X‐ray diffraction. Electrochemical investigations reveal that the complexes reduce protons at their first reduction potential, resulting in the lowest overpotential (120 mV) ever reported for [FeFe]‐H2ase mimics in proton reduction catalysis when mild acid (phenol) is used as proton source