Insight into the Mechanism of Dihydrogen‐Heterolysis at Cyclopentadienone Iron Complexes and Subsequent CX Hydrogenation

Abstract

AbstractA 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 H2, 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.