From ferrocene to 1,2,3,4,5-pentafluoroferrocene: halogen effect on the properties of metallocene

Abstract

Impact of successive fluorinations onto redox, spectroscopic and NMR properties of ferrocene.

Preparation and One-Electron Oxidation of Decabromoferrocene

“…The comparison of these results with less brominated metallocenes (FeC 10 BrH 9 , E 1/2 = 0.110 V vs FeCp 2 0/+ ; see Table 1) shows that the oxidation potentials continuously increase with the level of bromination. This finding is consistent with the results for polyfluorinated FeC 10 F n H 10−n (n = 0, 1, 2, 3, 4, 5) 30 and polychlorinated metallocenes FeC 10 H 10−n Cl n (n = 1, 2, 5, 10). 24 This correlation was found to be linear for ferrocenes bearing the lighter halogens atoms (F, Cl) but not for brominated ferrocenes (this work).…”

“…While for mono- and disubstituted ferrocenes these correlations fit quite well (Figure ), the discrepancies become most visible at high halogenation levels. This is consistent with the results of Erb and co-workers, who showed that in the case of (poly)­halogenated ferrocenes the correlation between the redox potentials and R falls into distinct groups depending on the substitutional pattern but is nonlinear over all investigated metallocenes . Therefore, the explanation cannot be restricted to Hammett constants but should consider, as discussed by Erb and Inkpen previously, orbital reordering, changes in hybridization and frontier orbital composition, electrostatic repulsion between metal and Cp ring orbitals, and through-space interactions between the iron center and halogen atoms. , …”

“…This is consistent with the results of Erb and co-workers, who showed that in the case of (poly)halogenated ferrocenes the correlation between the redox potentials and R falls into distinct groups depending on the substitutional pattern but is nonlinear over all investigated metallocenes. 30 Therefore, the explanation cannot be restricted to Hammett constants but should consider, as discussed by Erb and Inkpen previously, orbital reordering, changes in hybrid-ization and frontier orbital composition, electrostatic repulsion between metal and Cp ring orbitals, and through-space interactions between the iron center and halogen atoms. 30,31 Since electrochemical measurements suggest the existence of the polybrominated ferrocenium cations, we were interested in the isolation of the oxidized species.…”

“…30 Therefore, the explanation cannot be restricted to Hammett constants but should consider, as discussed by Erb and Inkpen previously, orbital reordering, changes in hybrid-ization and frontier orbital composition, electrostatic repulsion between metal and Cp ring orbitals, and through-space interactions between the iron center and halogen atoms. 30,31 Since electrochemical measurements suggest the existence of the polybrominated ferrocenium cations, we were interested in the isolation of the oxidized species. In the neutral compounds, the iron Cp bonds are 0.03 Å shorter than in unsubstituted ferrocene, which was already observed in other halogenated metallocenes.…”

Exploring the boundaries of ferrocenesulfonyl fluoride chemistry

“…Indeed, many other factors such as orbitals ordering, changes in hybridization and frontier orbital composition, through-space interaction between the metal and the substituents as well as electrostatic repulsion between the metal and the Cp ring orbitals need to be considered. 147,151,154 Therefore, a better understanding of the substituent effect on the redox potential of a hetero polysubstituted ferrocene would require a dedicated study, which falls out the scope of this work.…”