Bonding analysis of the neutral electrophilic phosphinidene complexes of vanadium and niobium [(η5-C5H5)(CO)3M(PNR2)] (R = Me, iPr, tBu): A DFT study

Density functional theory (DFT) calculations have been performed on the neutral electrophilic phosphinidene complexes [(η5-C5H5)(CO)3M(PNR2)] (M = V, Nb; R = Me, iPr, tBu) at BP86/TZ2P/ZORA level of theory. The calculated geometry parameters of the complex [(η5-C5H5)(CO)3V(PNR2)] are in good agreement with their available experimental values. On the basis of Mayer bond order analysis, the M–P bonds in all the studied complexes are found to be shorter than the M–P single bonds. On going from R = methyl to R = tertiary butyl, the optimized M–P bond distances increase. The observed geometry parameters are well supported by the results of energy decomposition analysis. The M–PNR2 bonds of the niobium complexes are slightly stronger than that of the vanadium complexes due to d-orbital extent. The orbital interactions between metal and PNR2 fragments in all complexes arise mainly from M ← PNR2 σ-donation; however, the M → PNR2 π back-donation also contributes significantly (24.1%–28.5%) to the total orbital contribution. The π back bonding contribution to the M–PNR2 bonds increases on going from M = V to M = Nb. The π back bonding increases going from R = Me < iPr < tBu. The σ-bonding orbitals in all studied complexes are well occupied.