Abstract
The equilibrium geometries and bond dissociation energies of the complexes L2TM-C2H2 and L2TM-C2H4(TM = Ni, Pd, Pt) with the monodentate ligands L2 = (PH3)2, (PMe3)2 and the bidentate ligands L2 = η2-disphosphinomethane (dpm), η2-disphosphinoethane (dpe) have been calculated using gradient-corrected DFT methods. The nature of the bonding interactions between the metal and the π ligands ethene and ethyne was investigated with an energy partitioning analysis (EPA). The ethene and ethyne ligands are more strongly bonded to the metal when L2 = dpm, dpe. The EPA results reveal that the reason for the stronger bonds of (dpm)TM - C2Hx and (dpe)TM - CH2Hx is the smaller preparation energy of (dpm)TM and (dpe)TM that is necessary to deform the metal fragments from the equilibrium geometry to the geometry in the complex. The L2TM-C2Hx interaction energies between the fragments with a frozen geometry do not significantly vary when L2 consists of a bidentate or two monodentate ligands. The EPA shows also that the nature of the L2TM-CH2Hx bonding does not change a lot when L2 = (PH3)2, (OMe3)2 or when L2 = dpm, dpe. The metal-carbon bonds always have a higher electrostatic (54.1-62.3%) than covalent (37.7-45.9%) character. The covalent bonding in the ethyne and ethene complexes comes mainly from the TM→C2Hx in-plane π back-donation, while the relative contribution of the TM←C2Hxσ donation is much less. The contributions of the out-of-plane a2(δ) and b1(π⊥) orbital interactions are very small even for the ethyne complexes. The bonding analysis suggests that the ethyne ligand in the complexes (PH3)2TM-C2H2 and (PMe3)2TM-C2H2 should be considered as a two-electron donor and not a four-electron donor.
| Original language | English |
|---|---|
| Pages (from-to) | 2758-2765 |
| Number of pages | 8 |
| Journal | Organometallics |
| Volume | 22 |
| Issue number | 13 |
| DOIs | |
| State | Published - 23 Jun 2003 |
| Externally published | Yes |