Shared electron versus donor–acceptor bonding description of Fe–ER bonds in [(η5-C5H5)(L)2Fe(ER)] (L = CO, PMe3; E = Si, Ge, Sn, Pb; R = Ph, Me)

Geometry and bonding energy analysis of Fe-E bonds in the ferrio-ylenes [(η5-C5H5)(L)2Fe(ER)] (L = CO, PMe3; E = Si, Ge, Sn, Pb; R = Ph, Me) were investigated at the DFT, DFT-D3 and DFT-D3(BJ) methods using density functionals (BP86, PW91, PBE, revPBE and TPSS). The TPSS functional yields better geometry and calculated geometrical parameters for the model ferrio-ylenes are in agreement with the experimental values for ferrio-ylenes. The Fe–E bonds in these complexes are essentially Fe–E single bonds. In all studied complexes, the π-bonding contribution to the total Fe–ER bond is significantly smaller than that of the σ-bonding. The electrostatic interactions ΔEelstat are larger than the covalent bonding ΔEorb terms in all ferrio-ylene complexes. The DFT-D3 method provide quite accurate estimate of the dispersion energy for the studied complexes. The contribution of dispersion interactions is large in computing accurate bond dissociation energies between the interacting metal fragments. The Fe–E bond dissociation energies (BDEs) with shared electron bonding follow the order revPBE < BP86 < TPSS < PBE < PW91. Significant finding of the present study is that the dispersion interactions are almost same for both the bonding models (shared electron and donor–acceptor models). The dispersion interactions are largest for complexes [(η5-C5H5)(PMe3)2Fe(EPh)] and smallest for [(η5-C5H5)(CO)2Fe(EMe)]. The strengths of dispersion interactions are sensitive to the (i) separation between the interacting fragments, (ii) size of ancillary ligands and (iii) substituent of the ligand fragment. The DFT-D3 dispersion corrections to the BDEs are smaller than the corresponding DFT-D3(BJ) dispersion corrections.