Iron–formaldehyde interaction: ‘ab initio’ calculations on the model compounds [Fe(CO)4–n(PH3)n(η2-CH2O)](n= 0, 2, or 4)

Abstract

‘Ab initio’ calculations have been performed on the model systems [Fe(CO)_4–n(PH₃)_n(η²-CH₂O)](n= 0, 2, or 4), to investigate the nature and the energetics of the interaction between iron and formaldehyde. The results allow a complete description of the electronic structure of the model compounds: the bond between Fe and CH₂O may essentially be described in terms of the π-back donation from an occupied metal orbital, of mainly d_xz character, to the π* orbital of formaldehyde. Partial geometry optimizations obtained by gradient calculations show that the geometry of the co-ordinated CH₂O is greatly distorted and the distortion increases with the substitution of carbonyl ligands with phosphines. Configuration-interaction calculations, performed on the [Fe(CO)₄(η²-CH₂O)] system using the direct configuration-interaction approach, suggest that the interaction energies computed at the Hartree–Fock level are reliable.