Anti-Kasha’s Rule Fluorescence Emission in (2-Ferrocenyl)indene Generated by a Twisted Intramolecular Charge-Transfer (TICT) Process

A twisted intramolecular charge-transfer (TICT) process has been identified in (2-ferrocenyl)indene. This photochemical process explains the anti-Kasha’s rule fluorescence emission observed for this system. Experimental and model investigations on (2-ferrocenyl)tetramethylindene and (2-ferrocenyl)-hexamethylindene were also performed, in order to evaluate the effect of a steric hindrance on the TICT mechanism. The energy of the lowest main excited states was computed with a TD-DFT approach, as a function of the rotation of the dihedral angle between the indene and the cyclopentadienyl planes. To the best of our knowledge, this is the first example of TICT generated by metal-to-ligand charge transfer (MLCT) in a ferrocene-containing complex and, more generally, the first case of complexes in which a metal center is directly involved

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

Heterobimetallic Indenyl Complexes. Kinetics and Mechanism of Substitution and Exchange Reactions of <i>trans</i>-[Cr(CO)₃-indenyl-Rh(CO)₂] with Olefins

The trans coordination of the benzene ring of the indenyl-Rh(CO)2 complex with tricarbonylchromium strongly enhances the rate of substitution of CO's with bidentate olefins, 1,5-cyclooctadiene (COD) and norbornadiene (NBD) (“extra-indenyl effect”). The activation parameters suggest an associative reaction pathway assumed to proceed via the intermediacy of a nonisolable low-hapticity species, η1-indenyl-Rh(CO)2(L2). In addition, the rate of exchange of the Cr(CO)3 group of the complexes trans-[Cr(CO)3-indenyl-Rh(CO)2], 3, and trans-[Cr(CO)3-indenyl-Rh(COD)], 3a, and suitable acceptors (hexamethylbenzene and cycloheptatriene) is markedly increased with respect to that measured for the same reaction in the monometallic complex η-naphthalene-Cr(CO)3 (“extra-naphthalene effect”). These mutual effects of the Cr(CO)3 and RhL2 units are transmitted through the 10 π electron indenyl framework, and the results obtained are in agreement with the existence of an haptomeric ground-state equilibrium between the two isomers trans-[Cr(CO)3-μ,η6:η3-indenyl-RhL2], I, and trans-[Cr(CO)3-μ,η4:η5-indenyl-RhL2], II

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

Heterobimetallic Indenyl Complexes. Mechanism of Cyclotrimerization of Dimethyl Acetylenedicarboxylate (DMAD) Catalyzed by <i>trans</i>-[Cr(CO)₃(Heptamethylindenyl)Rh(CO)₂ ]^†

The complex trans-[Cr(CO)3(heptamethylindenyl)Rh(CO)2] (II) is a very efficient catalyst precursor in the cyclotrimerization reaction of dimethyl acetylenedicarboxylate (DMAD) to hexacarbomethoxybenzene. The formation of the “true” catalyst, likely to be the complex trans-[Cr(CO)3−Ind*−Rh(DMAD)2], is the slow step of the reaction and takes place during the induction period, the length of which is temperature dependent. After total consumption of the monomer two organometallic complexes were isolated from the inorganic residue, viz., the catalyst precursor II and the complex trans-[Cr(CO)3−Ind*−Rh(CO)(FADE)] (III; FADE = fumaric acid dimethyl ester), which turns out to be active in the trimerization reaction as II. The hydrogenation of DMAD to FADE is probably occurring via C−H bond activation of the solvent cyclohexane

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