Theoretical investigation of triple bond in molybdenum complexes trans-[X(PMe3)4 MoE(Mes)] (X = F, Cl, Br, I; E = Si, Ge, Sn, Pb): A DFT study

Quantum-chemical calculations were used to investigate the molecular and electronic structures as well s bonding energies of the molybdenum-ylidyne complexes trans-[X(PMe3)(4)Mo=E(Mes)] (X = F, Cl, Br, I; E = Si, Ge, Sn, Pb) at the BP86/TZ2P/ZORA level of theory. The calculated geometrical results are in excellent agreement with the available experimental results. The Mo=E bond distances are significantly short, and the calculated Pauling Mo-E bond orders are similar to 2.40-2.65. The electronic structures of the Mo=E bonds show the presence of genuine triple bond containing an sigma-bond and two pi-bonds in all studied complexes. The Mo=E sigma-bonds are polarized towards the heavier group 14 elements while the pi-bonds are polarized towards the molybdenum metal. The partial charges on the [EMes](+) fragments (0.67-0.93) indicate that the overall charges flow from the metal fragments to the [EMes](+) fragments. The nature of Mo=E bonds also investigated by means of energy decomposition analysis which reveals that the metalligand pi-orbital interactions between [X(PMe3)(4)Mo](-) and [EMes](+) fragments are the most dominant interactions, contributing (80-85%) to the total Delta E-orb terms. The strength of Mo=E bonds mainly depends on the pi-acceptor ability of [EMes](+) group. It decreases when 14 group element becomes heavier in the trend Si > Ge > Sn > Pb and in the order F > Cl > Br > I. (C) 2012 Elsevier Ltd. All rights reserved.