Efficient Electronic Structure to Stabilize N2‐Bridged Dinuclear Complexes Intended for N2 Activation: Iminophosphorane Iron(I) and Cobalt(I)

Abstract

We examined the stability of the N2‐ligated mononuclear and N2‐bridged dinuclear complexes for FeI and CoI with the tridentate iminophosphorane ligand, which are in potentially deactivated state for catalytic N2 fixation processes, using density functional theory (DFT) method. The calculated Gibbs free energies of the N2 binding and N2‐bridge formation reactions show that the N2‐bridged FeI‐dinuclear complex is more favorable than the N2 FeI‐mononuclear complex in contrast to the CoI‐mononuclear complexes, which is only the available complex, even if at –80 °C. The stability of the N2‐bridged dinuclear metal complexes has a close relation to the M–N2 bond strength ruled by occupation of the pairs of dπu orbitals, in which the ungerade couples of the dπ orbitals interact with the occupied π orbitals of N2 in antibonding manner. For the catalytic activity of FeI mononuclear complexes, the appropriate order of orbitals to occupy the dπu orbitals is necessary, which is produced by the T‐shaped coordination geometry the ancillary ligands construct.