ORBITAL INTERACTIONS IN SIZABLE SYSTEMS - CHEMICAL BONDINGS AND REGIOSELECTIVITIES IN C-60 TRANSITION-METAL COMPLEXES

Chemical interactions in large and complicated systems are not easy to assess by means of the usual orbital interaction scheme based on perturbation theory. By taking a transition metal complex of buckminsterfullerene C60, we show that a simple manipulation gives rise to a clear view of interactions. It is demonstrated that the lowest unoccupied MO cooperates with the low-lying unoccupied MOs and the highest occupied MOs cooperate with the high-lying MOs in C60 to give rise to the localized interacting orbitals. The orbital interactions involved in (PH3)2Pt(eta2-C60) are seen to be very similar to the donation and back-donation of electrons in the transition metal complexes of small alkenes. On the basis of this analysis, the regioselectivity in multiple addition products is discussed.