On the possibility of existence of eta(5)-pi-complexes of C-60 fullerene: pi-complexes with silicon

Qualitative estimates of possibility of the formation of fullerene eta(5)-pi-complexes have been carried out by the MNDO/PM3 method. It was shown, as exemplified by the C-60 cluster, that the introduction of five univalent functional groups R (R = H, Cl, Br) to alpha-positions of a separate pentagon of C-60 with the formation of [R(5)C(60)](-) anions results in a pronounced increase in the pi-electron density on the atoms of this five-membered cycle and more favorable conditions for the formation of pi-bonds with the eta(5)-ligand. The nature of the interaction between the atoms of the separate cycle in [R(5)C(60)](-) anion and eta(5)-ligand was analyzed by the example of hypothetical sandwich systems R(5)C(60)SiCp. Half-sandwich complexes R(5)C(60)SiX (X = H, CI) were also investigated. The local energy minima were found on the potential energy surfaces (PES) of systems R(5)C(60)SiCp and R(5)C(60),SiX with C-5v symmetry. These systems transform barrirlessly into eta(5)-pi-complexes with the angular structure if the symmetry restrictions are removed. The most favorable conditions for eta(5)-pi-complexes of R(5)C(60) to form are realized for R = H. The results obtained were compared to those of semiempirical and nonempirical calculations of bis (cyclopentadienyl) silicon.