Theoretical investigation of M≡E bonds in transition metal–ylidyne complexes trans-[H(PMe3)4M≡ER] (M = Mo, W; E = Si, Ge, Sn, Pb; R = Mes, Xylyl)

The electronic structures and bond dissociation energies of the hydrido- transition metal–ylidyne complexes trans-[H(PMe3)4M≡ER] (M = Mo, W; E = Si, Ge, Sn, Pb; R = Mes, Xylyl) have been investigated using density functional theory at BP86/TZ2P/ZORA level. The calculated geometries are in excellent agreement with available experimental values. Pauling bond order shows that the M-E bonds in these complexes are nearly M≡E multiple bonds. The EDA results indicate that the absolute values of ∆Eint., ∆Eelstat, ∆Eorb, ∆EPauli and bond dissociation energies decrease in the order Si > Ge > Sn > Pb, and tungsten complexes have stronger bonding than the molybdenum complexes. The contribution of electrostatic interaction ∆Eelstat to the M–ER bonding is comparable to, or in some cases even slightly larger than the covalent bonding ∆Eorb. The σ-bonding interactions are significantly poor (less than 20%) and [H(PMe3)4M]− → ER+ π back-donation is dominant interaction in the studied metal–ylidyne complexes. The WBI values of the M-E bonds are significantly large (1.78–2.06). The NBO analysis indicates that the σ-bonding and both π-bonding orbitals are well occupied (>1.703e). The M-E σ-bonding orbitals are slightly polarized towards the heavier group 14 element while the π-bonding orbitals are highly polarized towards the metal atom.