Ab initio MO LCAO SCF simulation of molecular and electronic structure of η5-π-C60H5XCp (X=Fe, Si) complexes.

The problem of existence of η⁵-π-complexes of unsubstituted fullerene I _h -C₆₀ and its cyclopentadienyl type derivative C₆₀H₅ ^. is discussed. Ab initio MO LCAO SCF calculations of hypothetical sandwich systems η⁵-π-C₆₀H₅XCp (X=Fe ( 1a), Si ( 1b)), the cationic complex C₆₀FeCp⁺ of unsubstituted C₆₀, and the C₆₀H₅ ^. radical were performed in the STO-3G and 3-21G basis sets. In the 1a, 1b, and C₆₀H₅ ^. systems, hydrogen atoms are attached to carbon atoms of fullerene i _h -C₆₀ at α-positions relative to the same pentagonal face ( pent ^*). In η⁵-complexes, XCp species are also coordinated to this face. According to calculations in the 3-21G basis set, the Fe- pent ^* bond energy in complex 1a is much higher than those of similar bonds in 1b and in the η⁵-π-C₆₀FECp⁺ cation (117 kcal mol⁻¹ vs. 37 and 64 kcal mol⁻¹, respectively) and is 7 kcal mol⁻¹ higher than the Fe−Cp bond energy in the classical sandwich system FeCp₂. The Fe...C _pent* and Fe...C_Cp distances in complex 1a are slightly shorter than the Fe...C distance in the ferrocene molecule. The spin populations in the C₆₀H₅ ^. radical are almost completely localized on the atoms of the pent ^* face, which must favor the formation of η⁵-π-complexes of this radical. [ABSTRACT FROM AUTHOR]