Endohedral analogs of ferrocene: ab initio theoretical predictions

The problem of the existence of endohedral analogs of ferrocene is discussed. It is shown that radical CorH5radical dot, where Cor is corannulene C20H10 and five atoms H are added to the α-positions relative to the five-membered cycle (pent*) of Cor, can form stable polyhedral dimer D2h-C40H30 (D). The ground state of D is triplet. The energy of dimerization of CorH5radical dot is equal to 175 kcal mol−1. The geometric and electronic structure of hypothetical endohedral complex D5d-2η5-Fe@D (1) and its isomer D5d-2η5-Fe(CorH5)2 (1b), which is a sandwich complex, are simulated by the ab initio MO LCAO SCF method (HF/3-21G). It is found that the energy of 1 is less than the energy of 1b by 171 kcal mol−1. The energies of the Fepent* bond in complexes 1 (115 kcal mol−1) and 1b (111 kcal mol−1) are close to those of the FeCp bond in bis(cyclopentadienyl)iron FeCp2 (110 kcal mol−1). Complex 1 and also complex D5d-2η5-Fe@C40H10 (2), carbon skeletons of which have an analogous structure to 1 and with ten H added to the α-positions relative to polar pentagons (pent*), can be considered as endohedral analogs of ferrocene. Atom Fe in these complexes interacts with atoms of both polar pentagons. The binding energy of the atom Fe with the polyhedral fragment C40H10 of 2 is a bit less than in 1 (on 6 kcal mol−1).