Coordination behaviour of the isolobal phosphoraneiminato and cyclopentadienyl ligands in TiCl3(NPH3), TiCl3Cp, ReO3(NPH3), and ReO3Cp

The phosphoraneiminato and cyclopentadienyl complexes TiCl3(NPH3) (1), ReO3 (NPH3) (2), TiCl3Cp (3), and ReO3Cp (4) have been investigated quantum chem ically at the BP86/TZ(2)P level of nonlocal density functional theory (DFT) . The metal-ligand bonds turn out to dissociate homolytically with the comp uted values for the corresponding bond dissociation energies amounting to 7 9.6 (1), 103.4 (2), 58.1 (3) and 45.0 (4) kcal/mol. Whereas the M-N-P unit in the titanium complex 1 is linear, we find a bent structure for the corre sponding rhenium complex 2 (angle Re-N-P = 136.4 degrees). It turns out tha t the potential energy surface of the phosphoraneiminato complexes is extre mely shallow with respect to the M-N-P angle; a variation over 50 degrees i s associated with an energy change of less than 2 kcal/mol. Furthermore, we have carried out a detailed analysis of the bonding in our model complexes to elucidate the difference in metal-ligand bond strengths between the iso lobal phosphoraneiminato and cyclopentadienyl ligands.