Density functional study of metallacumulene complexes

Density functional calculations have been carried out on the series of meta llacumulene complexes [(CO)(5)Cr(=C)(n)H-2)] (n = 2-9) to study the electro nic structure and the bonding of the CnH2 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 experime ntal data. The electronic structure has been analyzed in terms of the syner gistic sigma donation pi back-donation model, and the contribution from pi back-donation was found to be slightly higher than that from a donation. Di ssociation energies have been calculated for the metal-cumulene bond and ha ve been found essentially independent of chain length. The perturbational t heory of reactivity has been employed to explain the reactivity patterns of this class of complexes.