Catalytic activation of H2 under mild conditions by an [FeFe]-hydrogenase model via an active μ-hydride species.

A [FeFe]-hydrogenase model (1) containing a chelating diphosphine ligand with a pendant amine was readily oxidized by Fc(+) (Fc = Cp2Fe) to a Fe(II)Fe(I) complex ([1](+)), which was isolated at room temperature. The structure of [1](+) with a semibridging CO and a vacant apical site was determined by X-ray crystallography. Complex [1](+) catalytically activates H2 at 1 atm at 25 °C in the presence of excess Fc(+) and P(o-tol)3. More interestingly, the catalytic activity of [1](+) for H2 oxidation remains unchanged in the presence of ca. 2% CO. A computational study of the reaction mechanism showed that the most favorable activation free energy involves a rotation of the bridging CO to an apical position followed by activation of H2 with the help of the internal amine to give a bridging hydride intermediate.