pH-Dependent isotope exchange and hydrogenation catalysed by water-soluble NiRu complexes as functional models for [NiFe]hydrogenases

The pH-dependent hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes and hydrogenation of the carbonyl compounds have been investigated with water-soluble bis(μ-thiolate)(μ-hydride)NiRu complexes, Ni^II(μ-SR)₂(μ-H)Ru^II {(μ-SR)₂ = N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)-1,3-propanediamine}, as functional models for [NiFe]hydrogenases. In acidic media (at pH 4–6), the μ-H ligand of the Ni^II(μ-SR)₂(μ-H)Ru^II complexes has H⁺ properties, and the complexes catalyse the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes. A mechanism of the hydrogen isotope exchange reaction between gaseous isotopes and medium isotopes through a low-valent Ni^I(μ-SR)₂Ru^I complex is proposed. In contrast, in neutral–basic media (at pH 7–10), the μ-H ligand of the Ni^II(μ-SR)₂(μ-H)Ru^II complexes acts as H⁻, and the complexes catalyse the hydrogenation of carbonyl compounds.