Accurate theoretical description of the M–PNR2 bonds in phosphinidene complexes of manganese and rhenium [(CO)5M–PNR2]+ (R = Me, iPr, tBu) and [(PMe3)(CO)4M–PNiPr2]+: A DFT-D3 study

Geometry and bond energy analysis of M–P bonds in the terminal phosphinidene complexes of manganese and rhenium [(CO)5M–PNR2]+ (R = Me, iPr, tBu) and [(PMe3)(CO)4M–PNiPr2]+ were investigated at the DFT, DFT-D3 and DFT-D3(BJ) methods using functionals (BP86, revPBE, PW91 and TPSS). In all studied complexes, the π-bonding contributions to the total M–P bonds are significantly smaller (12.4–16.0%) than the σ-bonding components. The phosphinidene (PNR2) ligands are predominantly σ-donors. The electrostatic interaction ΔEelstat, in all complexes I–VIII, are larger than the orbital energies ΔEorb, which means, the M–PNR2 bonds in these complexes have greater degree of ionic characters (more than 50%). 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 fragments. The BDEs are largest for the functional PW91 and smallest for the functional revPBE. The dispersion corrections are in the range 6.4–11.1 kcal/mol (BP86), 7.2–8.6 kcal/mol (revPBE) and 5.7–8.6 kcal/mol (TPSS), which are smaller than the corresponding DFT-D3(BJ) dispersion corrections 7.6–11.8 kcal/mol (BP86), 8.7–12.8 kcal/mol (revPBE) and 5.8–9.0 kcal/mol (TPSS). The dispersion corrections calculated by DFT-D3 scheme increase on going from M = Mn to M = Re and smallest for the complexes [(PMe3)(CO)4M(PNiPr2)]+.