Density Functional Study of Metallacumulene Complexes

Density functional calculations have been carried out on the series of metallacumulene complexes [(CO) 5 Cr( C) n H 2 )] ( n = 2−9) to study the electronic structure and the bonding of the C n H 2 cumulene carbene moieties to d 6 transition metal fragments. Optimized geometries have been calculated for all complexes and found in good agreement with the available X-ray experimental data. The electronic structure has been analyzed in terms of the synergistic σ donation π back-donation model, and the contribution from π back-donation was found to be slightly higher than that from σ donation. Dissociation energies have been calculated for the metal−cumulene bond and have been found essentially independent of chain length. The perturbational theory of reactivity has been employed to explain the reactivity patterns of this class of complexes.