Theoretical investigation of ME bonds in transition metal-ylidyne complexes trans-[H(PMe3)4MER] (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)(4)M 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 Delta E-int, Delta E-elstat, Delta E-orb, Delta E-Pauli 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 Delta E-elstat to the M-ER bonding is comparable to, or in some cases even slightly larger than the covalent bonding Delta E-orb. The sigma-bonding interactions are significantly poor (less than 20%) and [H(PMe3)(4)M](-) -> ER+ pi 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 sigma-bonding and both pi-bonding orbitals are well occupied (> 1.703e). The M-E sigma-bonding orbitals are slightly polarized towards the heavier group 14 element while the pi-bonding orbitals are highly polarized towards the metal atom. (C) 2012 Elsevier B.V. All rights reserved.