Charge Transfer Properties of Multi(ferrocenyl)trindenes

Ferrocenyl, diferrocenyl, and triferrocenyl complexes of dihydro-1<i>H</i>-trindene have been prepared by up to 3-fold bromide substitution of the dihydro-2,5,8-tribromo-1<i>H</i>-trindene halocarbon. The charge transfer properties of their mono-, di-, and tricationic derivatives were investigated. The cations of this new family of multi­(ferrocenyl)­trindene complexes were generated by chemical oxidation using (acetylferrocenium)­(BF₄) as the oxidative agent and monitored in the visible, IR and near-IR regions. The charge transfer bands in the near-IR spectra are rationalized in the framework of the Marcus–Hush theory. In particular, the triferrocenyl complexes display a redox chemistry that can be switched from a unresolved three-electron oxidation to two consecutive one-electron and two near simultaneously occurring one-electron oxidations by changing the supporting electrolyte from [<i>n</i>Bu₄N]­[PF₆] to [<i>n</i>Bu₄]­[B­(C₆F₅)₄]. In addition, the introduction of the third ferrocenyl group increases the strength of the metal–metal interaction with respect to that of the structurally related diferrocenyl system

Single Two-Electron Transfers and Successive One-Electron Transfers in Biferrocenyl−Indacene Isomers

Novel biferrocenyl complexes of s- and as-dihydroindacenes have been prepared and the charge transfer properties of their mono- and dicationic derivatives, selectively generated by one-electron and two-electron oxidation, have been investigated. Mixed-valence cations are generated by chemical oxidation using acetylferricinium as an oxidant agent and monitored in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory. The rigid and planar indacene platform bonded to two terminal redox groups displays a redox chemistry that can be switched from single two-electron transfers to two successive one-electron transfers by changing the supporting electrolyte from nBu4NPF6 to nBu4NB(C6F5)4

Single Two-Electron Transfers and Successive One-Electron Transfers in Biferrocenyl−Indacene Isomers

Novel biferrocenyl complexes of s- and as-dihydroindacenes have been prepared and the charge transfer properties of their mono- and dicationic derivatives, selectively generated by one-electron and two-electron oxidation, have been investigated. Mixed-valence cations are generated by chemical oxidation using acetylferricinium as an oxidant agent and monitored in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory. The rigid and planar indacene platform bonded to two terminal redox groups displays a redox chemistry that can be switched from single two-electron transfers to two successive one-electron transfers by changing the supporting electrolyte from nBu4NPF6 to nBu4NB(C6F5)4

Charge Transfer Properties of Benzo[<i>b</i>]thiophene Ferrocenyl Complexes

The synthesis of 2-ferrocenylbenzo­[<i>b</i>]­thiophene, 3-ferrocenylbenzo­[<i>b</i>]­thiophene, 1,1′-bis­(2-indene)­ferrocene, and the two isomers of 1,1′-bis­(2-benzo­[<i>b</i>]­thiophene)­ferrocene was efficiently achieved by using the palladium-catalyzed Negishi C,C cross-coupling reaction of the appropriate bromobenzo­[<i>b</i>]­thiophene derivative with ferrocenylzinc chloride. The accessibility of differently substituted benzo­[<i>b</i>]­thiophenes and a comparison with indene analogues allowed an in-depth investigation on how the geometric modifications and the presence of sulfur affect their physical properties. The molecular structure of 3-ferrocenylbenzo­[<i>b</i>]­thiophene has been determined by X-ray diffraction. Electrochemistry and UV–vis–NIR spectroscopy, in particular the appearance upon oxidation of a charge transfer absorption in the NIR region, are rationalized through quantum chemistry calculations and in the framework of the Hush theory

Charge Transfer Properties of Benzo[<i>b</i>]thiophene Ferrocenyl Complexes

The synthesis of 2-ferrocenylbenzo­[<i>b</i>]­thiophene, 3-ferrocenylbenzo­[<i>b</i>]­thiophene, 1,1′-bis­(2-indene)­ferrocene, and the two isomers of 1,1′-bis­(2-benzo­[<i>b</i>]­thiophene)­ferrocene was efficiently achieved by using the palladium-catalyzed Negishi C,C cross-coupling reaction of the appropriate bromobenzo­[<i>b</i>]­thiophene derivative with ferrocenylzinc chloride. The accessibility of differently substituted benzo­[<i>b</i>]­thiophenes and a comparison with indene analogues allowed an in-depth investigation on how the geometric modifications and the presence of sulfur affect their physical properties. The molecular structure of 3-ferrocenylbenzo­[<i>b</i>]­thiophene has been determined by X-ray diffraction. Electrochemistry and UV–vis–NIR spectroscopy, in particular the appearance upon oxidation of a charge transfer absorption in the NIR region, are rationalized through quantum chemistry calculations and in the framework of the Hush theory

Charge Transfer Properties in Cyclopenta[<i>l</i>]phenanthrene Ferrocenyl Complexes

The new complexes (2-ferrocenyl)­cyclopenta­[<i>l</i>]­phenanthrene and (2-ferrocenyl)­(η⁵-cyclopenta­[<i>l</i>]­phenanthrenyl)­FeCp have been prepared and the charge transfer properties of their monocationic derivatives investigated. The cations were generated by chemical oxidation using ferrocenium­(BF₄) or acetylferrocenium­(BF₄) as the oxidative agent and monitored in the visible, IR, and near-IR regions. The electrochemistry of the two complexes and, for comparison, of the previously reported (η⁵-cyclopenta­[<i>l</i>]­phenanthrenyl)­FeCp was analyzed. The charge transfer bands in the near-IR spectral region of the monocations are rationalized in the framework of Marcus–Hush theory. In particular, the monometallic (2-ferrocenyl)­cyclopenta­[<i>l</i>]­phenanthrene displays a single oxidation wave at a potential very close to that of (η⁵-cyclopenta­[<i>l</i>]­phenanthrenyl)­FeCp and its monocations exhibits a ligand-to-metal charge transfer band in the vis–near-IR region. The unsymmetrical diiron species (2-ferrocenyl)­(η⁵-cyclopenta­[<i>l</i>]­phenanthrenyl)­FeCp undergoes two consecutive and well-resolved one-electron oxidations producing, at the first oxidation step, a mixed-valence monocation which displays an intervalence charge transfer band in the vis–near-IR region

Charge Transfer Properties of Benzo[<i>b</i>]thiophene Ferrocenyl Complexes

The synthesis of 2-ferrocenylbenzo­[<i>b</i>]­thiophene, 3-ferrocenylbenzo­[<i>b</i>]­thiophene, 1,1′-bis­(2-indene)­ferrocene, and the two isomers of 1,1′-bis­(2-benzo­[<i>b</i>]­thiophene)­ferrocene was efficiently achieved by using the palladium-catalyzed Negishi C,C cross-coupling reaction of the appropriate bromobenzo­[<i>b</i>]­thiophene derivative with ferrocenylzinc chloride. The accessibility of differently substituted benzo­[<i>b</i>]­thiophenes and a comparison with indene analogues allowed an in-depth investigation on how the geometric modifications and the presence of sulfur affect their physical properties. The molecular structure of 3-ferrocenylbenzo­[<i>b</i>]­thiophene has been determined by X-ray diffraction. Electrochemistry and UV–vis–NIR spectroscopy, in particular the appearance upon oxidation of a charge transfer absorption in the NIR region, are rationalized through quantum chemistry calculations and in the framework of the Hush theory

Charge Mapping in 3₁₀-Helical Peptide Chains by Oxidation of the Terminal Ferrocenyl Group

Two series of 310-helical peptides of different lengths and rigidity, based on the strongly foldameric α-aminoisobutyric acid and containing a terminal ferrocenyl unit, have been synthesized. Oxidation-state sensitive spectroscopic tags of helical peptides, the N−H groups, allowed mapping of the charge delocalization triggered by oxidation of the terminal ferrocenyl moiety and were monitored by IR spectroelectrochemistry

Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)−Rh(I)−Cr(0) Triads of the Polyaromatic Cyclopentadienyl−Indenyl Ligand

The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of η6-Cr(CO)3{η5-[(2-ferrocenyl)indenyl]Rh(CO)2} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal−metal (Fe−Cr) interaction with respect to the structurally correlated binuclear system

Intervalence Charge Transfer in Cationic Heterotrinuclear Fe(III)−Rh(I)−Cr(0) Triads of the Polyaromatic Cyclopentadienyl−Indenyl Ligand

The challenge to realize polymetallic assemblies of unambiguous structure and stereochemistry, in which the nature of the intervalence transition (IT) is rationalized, has been faced by investigating the syn and anti isomers of η6-Cr(CO)3{η5-[(2-ferrocenyl)indenyl]Rh(CO)2} and their mixed-valence cations. Crystallographic studies and DFT calculations provide a detailed description of the structural and electronic features of these complexes, evidencing a significant difference in geometrical distortions and frontier MO composition between syn and anti isomers. Mixed-valence cations are generated and monitored by low-temperature spectroelectrochemistry in the visible, IR, and near-IR regions. The IT bands in the near-IR spectra are rationalized in the framework of Marcus−Hush theory and at quantum chemistry level by density functional theory. Noteworthy, the results reported provide rare experimental evidence that the presence of a third metal center (Rh) increases the metal−metal (Fe−Cr) interaction with respect to the structurally correlated binuclear system