COMPUTATIONAL STUDY OF RING-PROTONATED AND METAL-PROTONATED FERROCENE

Protonated ferrocene was studied at several different levels of theory. Geometries were optimized at the Hartree-Fock level with an effective core potential for iron and a 6-31G* basis for carbon and at the MP2 level of electron correlation with an all-electron basis. The largest basis set used included a 6-31G* basis on carbon and triple-zeta d-functions plus f-functions on iron. At the HF level, the ring-protonated site is favored over the metal-protonated site, but electron correlation at the MP2 level has a very large effect on the relative energy of the two structures and causes a reversal in the preferred site. While geometries found including electron correlation are considerably different from HF geometries, the preference for metal protonation is maintained. Interestingly, an entirely different mode of binding is predicted for ring protonation at the MP2 level of geometry optimization. Analysis of the charges and metal populations indicates that metal protonation causes nearly a full electron to be transferred from the rings to the metal. On the other hand, if the ring is protonated, the charge on iron does not substantially change.