A PICTORIAL MO DESCRIPTION OF BUCKMINSTERFULLERENE AND ITS INTERACTIONS WITH TRANSITION-METAL FRAGMENTS

The highly delocalized distribution of the MOs in C60 has been analyzed with the aid of extended Huckel calculations and their graphic representations. Symmetry and perturbation theory arguments rationalize the MO correlations in terms of the implosion of 12 C5 rings distributed at the vertices of an expanded icosahedron. In particular, two distinguishable sigma and pi C60 subsets are each split into 30 filed and 30 empty MOs belonging to the same species under I(h) symmetry. As a major difference, whereas 30 new C-C sigma bonds add to the 60 pre-existing C5 endocyclic bonds, some partial pi bonding at the 6:6 edges of C60 occurs at the expense of pi bonding at the 5:6 edges. This point has been clarified by referring to the electronic structure of the simpler molecule [5]-radialene which typifies the MO response to the idea of pi resonance. An overview at the C-C bonding/antibonding roles in all of the pi MOs simplifies understanding their possible interactions with the frontier MOs of typical transition metal fragments. The model complexes considered involve the eta2-coordination of the C2v fragment (PH3)2Pt to C60 in 6:1, 2:1 and 1:1 ratios. The MO analysis highlights the electronic causes of the deformation from sphericity of C60 when a metal is attached to one or more 6:6 edge. Attempts to explore alternative, but as yet unsynthesized coordination modes have also been made.