Strategies to stabilize exohedral eta 5-and eta 6-fullerene transition metal organometallic complexes: A molecular orbital treatment

Transition metal fragments are designed to overcome the unfavourable,intera ction arising from the splayed-out pi-orbitals of the five- and six-membere d rings of C-60 in complex formation. Semiemprical studies at the PMS(tm) l evel on a series of C60MCnHn complexes suggest that, with the appropriate t ransition metal fragment, it is possible to stabilize eta(6)- complexes of C-60. Isodesmic equations of the type CmHmMCnHn + C-60 --> C60MCnHn + CmHm indicate that C3H3Co and C3H3Rh are ideal fragments in stabilizing eta(6)-C -60 complexes. In comparison, eta(5)-complexes are less favourable; structu ral modifications such as those in the recently synthesized C60Ph5- should readily help eta(5)-bonding.