Metal-phosphorus bonding in Fe(CO)(4)PR3 complexes. A density functional study

Fe(CO)(4)PR3 complexes have been studied for R = H, Me, Ph, OMe, F, i-Pr, and NC4H4 using density functional methods. The Fe-PR3 bond has been analyzed in terms of steric and electronic effects. The results obtained show that the main contribution to the bond stems always from the sigma donation, but phosphines can be classified into three groups depending on the relative magnitude of the pi-back-donation contribution. Thus, PMe3, PPh3, and P(i-Pr)(3) can be considered as sigma-donor ligands, PF3 and P(NC4H4)(3) would be sigma-donor/pi-acceptor ligands, and PH3 and P(OMe)(3) would correspond to intermediate cases.