Assessment of density functionals and paucity of non-covalent interactions in aminoylyne complexes of molybdenum and tungsten [(η5-C5H5)(CO)2MEN(SiMe3)(R)] (E = Si, Ge, Sn, Pb): a dispersion-corrected DFT study

Abstract

Electronic, molecular structure and bonding energy analyses of the metal–aminosilylyne, –aminogermylyne, –aminostannylyne and –aminoplumbylyne complexes [(η⁵-C₅H₅)(CO)₂MEN(SiMe₃)(Ph)] (M = Mo, W) and [(η⁵-C₅H₅)(CO)₂MoGeN(SiMe₃)(Mes)] have been investigated at DFT, DFT-D3 and DFT-D3(BJ) levels using BP86, PBE, PW91, RPBE, TPSS and M06-L functionals. The performance of metaGGA functionals for the geometries of aminoylyne complexes is better than GGA functionals. Significant dispersion interactions between O⋯H, E⋯C(O) and E⋯H pairs appeared in the dispersion-corrected geometries. The non-covalent distances of these interactions follow the order DFT > DFT-D3(BJ) > DFT-D3. The values of Nalewajski–Mrozek bond order (1.22–1.52) and Pauling bond order (2.23–2.59) of the optimized structures at BP86/TZ2P indicate the presence of multiple bonds between metal and E atoms. The overall electronic charges transfer from transition-metal fragments to ligands. The topological analysis based on QTAIM has been performed to determine the analogy of non-covalent interactions. The strength of MEN(SiMe₃)(R) bonds has been evaluated by energy decomposition analysis. The electrostatic interactions are almost equal to orbital interactions. The M ← E σ-donation is smaller than the M → E π-back donation. Upon going from E = Si to E = Pb, the M–E bond orders decrease as Si > Ge > Sn > Pb, consistent with the observed geometry trends. The M–E uncorrected bond dissociation energies vary with the density functionals as RPBE < BP86 < PBE < TPSS < PW91. The largest DFT-D3 dispersion corrections to the BDEs correspond to the BP86 functional, ranging between 5.6–8.1 kcal mol⁻¹, which are smaller than the DFT-D3(BJ) dispersion corrections (10.1–12.0 kcal mol⁻¹). The aryl substituents on nitrogen have an insignificant effect on M–E–N bending. The bending of the M–E–N bond angle has been discussed in terms of Jahn–Teller distortion. The larger noncovalent interaction and smaller absolute values of ΔE(HOMO–LUMO) with the M06-L functional are responsible for lowering the M–E–N bond angle.