Computational Design of Iron Diphosphine Complexes with Pendant Amines for Hydrogenation of CO2 to Methanol: A Mimic of [NiFe] Hydrogenase

Inspired by the active-site structure of the [NiFe] hydrogenase, we have computationally designed the iron complex [(P2N2tBu)-N-tBu)Fe(CN)(2)CO] by using an experimentally ready-made diphosphine ligand with pendant amines for the hydrogenation of CO2 to methanol. Density functional theory calculations indicate that the rate-determining step in the whole catalytic reaction is the direct hydride transfer from the Fe center to the carbon atom in the formic acid with a total free energy barrier of 28.4 kcal mol(-1) in aqueous solution. Such a barrier indicates that the designed iron complex is a promising low-cost catalyst for the formation of methanol from CO2 and H-2 under mild conditions. The key role of the diphosphine ligand with pendent amine groups in the reaction is the assistance of the cleavage of H-2 by forming a Fe-H delta-center dot center dot center dot H delta+-N dihydrogen bond in a fashion of frustrated Lewis pairs.