Heterolytic cleavage of hydrogen by an iron hydrogenase model: An Fe-H⋯H-N dihydrogen bond characterized by neutron diffraction

Hydrogenase enzymes in nature use hydrogen as a fuel, but the heterolytic cleavage of H-H bonds cannot be readily observed in enzymes. Here we show that an iron complex with pendant amines in the diphosphine ligand cleaves hydrogen heterolytically. The product has a strong Fe-H⋯H-N dihydrogen bond. The structure was determined by single-crystal neutron diffraction, and has a remarkably short H⋯H distance of 1.489(10) Å between the protic N-H^δ+ and hydridic Fe-H^δ- part. The structural data for [Cp C 5F 4NFeH(P^tBu₂N^tBu ₂H)]⁺ provide a glimpse of how the H-H bond is oxidized or generated in hydrogenase enzymes. These results now provide a full picture for the first time, illustrating structures and reactivity of the dihydrogen complex and the product of the heterolytic cleavage of H₂ in a functional model of the active site of the [FeFe] hydrogenase enzyme. Caught in the act: The addition of H₂ to a synthetic iron complex containing a pendant amine (a model complex for [FeFe] hydrogenase) leads to facile heterolytic cleavage of H₂. Neutron diffraction indicates a very short H⋯H bond distance of 1.489(10) Å in the Fe-H⋯H-N complex, thus providing a glimpse of how the H-H bond is oxidized in hydrogenase enzymes.