Ability of fullerenes to act as η6 ligands in transition metal complexes. A comparative PM3(tm)–density functional theory study

High‐quality DFT calculations are employed to estimate the arene exchange energies for reactions of general formula: For C₆₀ and C₇₀ complexes of Cr(CO)₃, full geometry optimizations at the DFT level using moderately large basis sets were performed, while for the other systems a hybrid approach was developed in which the geometries were obtained at the PM3(tm) level and the energetics were evaluated at the DFT level. C₇₀ is shown to be a slightly better arene ligand than C₆₀; however, no enhancements of arene‐like bonding capabilities are seen for C₇₈ and C₈₄ relative to C₇₀. Explicit calculation of a series of exchange energies at the DFT level using both DFT and PM3(tm) geometries demonstrates that PM3(tm) geometries are sufficiently accurate for the calculation of energetics at a higher theoretical level, but PM3(tm) calculations are inadequate for a quantitative assessment of exchange energies. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1881–1886, 2001