Insight into the Mechanism of Dihydrogen‐Heterolysis at Cyclopentadienone Iron Complexes and Subsequent CX Hydrogenation

A bifunctional iron‐based catalyst ( 7 ), a compound related to the [Fe]‐ or Hmd‐hydrogenase, was studied by using experimental and computational methods. Catalyst 7 bears a protic hydrogen atom at the ligand and a hydridic hydrogen atom at the iron atom, which originate from the heterolytic uptake of H 2 , and can be transferred to unsaturated molecules (i.e. carbonyl compounds and imines). Our DFT calculations indicate that a non‐classical dihydrogen‐iron complex exists, and that the hydrogen uptake is an exergonic process. The hydrogenation of carbonyl compounds proceeds through a synchronous, concerted outer‐sphere mechanism, whereas the hydrogenation of the imine 18 is a two‐step process. In the first step, the imine is protonated to afford an iminium ion, to which the hydride is then transferred in a second reaction step. Energy hypersurfaces were calculated by using a solvent (toluene) continuum model.