Haptotropic shifts in mononuclear complexes of substituted pentalenes: A DFT investigation of the [CpFe(C8H4R2)]q (R = H, Me, NH2, CF3, CN ; q = −1, 0, +1) series

The haptotropic migration of Fe from the unsubstituted ring to the substituted one in the pentalenic complexes [CpFe(η5-1,3 C8H4R2)]q (q = +1, 0, −1) has been investigated by the means of DFT calculations in the case of R = H, CH3, NH2, CF3 and CN. The low energy pathway is a least-motion one-step process in the cationic case. In the anionic series, it is a two-step process involving an intermediate in which the metal moiety is η3-bonded in an exocyclic way to the pentalene ligand. The activation barriers and the preference for the Fe coordination on one ring rather on the other one is investigated with respect to the donor or acceptor abilities of R. The effect of changing q on the haptotropic situation is analyzed in terms of redox molecular switching.