• enzyme models;
  • hydrogen;
  • hydrogenases;
  • iron;
  • neutron diffraction


Hydrogenase enzymes in nature use hydrogen as a fuel, but the heterolytic cleavage of H[BOND]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-Hδ+ and hydridic Fe-Hδ− part. The structural data for [Cpinline imageFeH(PtBu2NtBu2H)]+ provide a glimpse of how the H[BOND]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.