| Abstract
| - The transition-metal fragment C3H3M is judged to be the best for η6 bonding to the fullerenes C60 and C70.
- Suitable transition-metal fragments are proposed to overcome the unfavorable interactionarising from the splayed out π-orbitals of the five- and six-membered rings of C60 and C70 incomplex formation. Computations carried out at the semiempirical PM3(tm) level on a seriesof C60MCnHn and C70MCnHn complexes suggest that it is possible to stabilize η6 complexesof C60 and C70 using appropriate transition-metal fragments. Isodesmic equations of the typeCmHmMCnHn + Ck → CkMCnHn + CmHm, where k = 60, 70, m = 5, 6, and n = 3−6, indicatethat C3H3Co and C3H3Rh are ideal fragments for stabilizing η6-C60 complexes. Model studiesat HF/LANL2DZ and B3LYP/LANL2DZ levels on C6H6MLn complexes with C6H6 constrainedso as to mimic the C60 geometry support these results. Single-point calculations at thesesame levels on complexes of sumanene (C21H12) using geometry optimized at the PM3(tm)method also lead to similar conclusions. η5 complexes are less favorable in comparison;structural modifications such as those in the recently synthesized C60Ph6 should readilyhelp in η5 bonding. However, the difficulty of formation of the mononuclear η5-C60MLn complexis reduced considerably if all 12 five-membered rings are used in η5 bonding as inC60(NiC3H3)12. For C70, however, the stability of the exohedral complexes depends on theposition and curvature of the five- and six-membered rings. Capping on the flattest six-membered face leads to maximum stability.
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