DENSITY-FUNCTIONAL CALCULATIONS OF THE STRUCTURES AND BOND-ENERGIES OF CR(CO)(6) AND (ETA(6)-C6H6)CR(CO)(2)(CX) (X=O, S) COMPLEXES

Quantum chemical calculations based on density functional theory have been performed on Cr(CO)(6), (eta(6)-C6H6)Cr(CO)(3) and (eta(6)-C6H6)Cr(CO)(2)(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (eta(6)-C6H6)Cr(CIO)(3) and (eta(6)-C6H6)Cr(CO)(2)(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger pi-backbonding charge transfer to the CS ligand as compared with CO.