Simple Ligand Effects Switch a Hydrogenase Mimic between H 2 and O 2 Activation

Herein, we report a [NiRu] biomimetic system for O 2 ‐tolerant [NiFe]hydrogenases and demonstrate that electron donation to the [NiRu] center can switch the system between the activation of H 2 and O 2 through simple ligand effects by using hexamethylbenzene and pentamethylcyclopentadienyl ligands, respectively. Furthermore, we present the synthesis and direct observations of a [NiRu]–peroxo species, which was formed by the oxygenation of a Ni‐SIa model [NiRu] complex, that we propose as a biomimetic analogue of O 2 ‐bound species (OBS) of O 2 ‐tolerant [NiFe]hydrogenases. The [NiRu]–peroxo complex was fully characterized by X‐ray analysis, X‐ray photoelectron spectroscopy (XPS), mass spectrometry, and 1 H NMR spectroscopy. The OBS analogue was capable of oxidizing p ‐hydroquinone and sodium borohydride to turn back into the Ni‐SIa model complex.