Endohedral analogs of ferrocene: ab initio theoretical predictions

Abstract

The problem of the existence of endohedral analogs of ferrocene is discussed. It is shown that radical CorH 5 , where Cor is corannulene C 20H 10 and five atoms H are added to the α-positions relative to the five-membered cycle ( pent*) of Cor, can form stable polyhedral dimer D 2 h -C 40H 30 (D). The ground state of D is triplet. The energy of dimerization of CorH 5 is equal to 175 kcal mol −1. The geometric and electronic structure of hypothetical endohedral complex D 5 d -2η 5-Fe@D ( 1) and its isomer D 5 d -2η 5-Fe(CorH 5) 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 FeCp 2 (110 kcal mol −1). Complex 1 and also complex D 5 d -2η 5-Fe@C 40H 10 ( 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 C 40H 10 of 2 is a bit less than in 1 (on 6 kcal mol −1).