Hybrid Molecular Systems Containing Tetrathiafulvalene and Iron‐Alkynyl Electrophores: Five‐Component Functional Molecules Obtained from CH Bond Activation

Abstract

Treatment of [Cp*(dppe)Fe-C≡C-TTFMe3] (1) with Ag[PF6] (3 equiv) in DMF provides the binuclear complex [Cp*(dppe)Fe=C=C=TTFMe2 =CH-CH=TTFMe2 =C=C=Fe(dppe)Cp*][PF6]2 (2[PF6 ]2) isolated as a deep-blue powder in 69 % yield. EPR monitoring of the reaction and comparison of the experimental and calculated EPR spectra allowed the identification of the radical salt [Cp*(dppe)Fe=C=C=TTFMe2 =CH][PF6]2 ([1-CH][PF6]) an intermediate of the reaction, which results from the activation of the methyl group attached in vicinal position with respect to the alkynyl-iron on the TTF ligand by the triple oxidation of 1 leading to its deprotonation by the solvent. The dimerization of [1-CH][PF6] through carbon-carbon bond formation provides 2[PF6]2. The cyclic voltammetry (CV) experiments show that 2[PF6]2 is subject to two sequential well-reversible one-electron reductions yielding the complexes 2[PF6] and 2. The CV also shows that further oxidation of 2[PF6]2 generates 2[PF6]n (n=3-6) at the electrode. Treatment of 2[PF6]2 with KOtBu provides 2[PF6] and 2 as stable powders. The salts 2[PF6] and 2[PF6]2 were characterized by XRD. The electronic structures of 2(n+) (n=0-2) were computed. The new complexes were also characterized by NMR, IR, Mössbauer, EPR, UV/Vis and NIR spectroscopies. The data show that the three complexes 2[PF6]n are iron(II) derivatives in the ground state. In the solid state, the dication 2(2+) is diamagnetic and has a bis(allenylidene-iron) structure with one positive charge on each iron building block. In solution, as a result of the thermal motion of the metal-carbon backbone, the triplet excited state becomes thermally accessible and equilibrium takes place between singlet and triplet states. In 2[PF6], the charge and the spin are both symmetrically distributed on the carbon bridge and only moderately on the iron and TTFMe2 electroactive centers.

Synthesis and Properties of a Mixed‐Valence Compound with Single‐Step Tunneling and Multiple‐Step Hopping Behavior

“…Pertinent geometrical data are given in Table S1. The optimized distances for the neutral system are similar to those computed for the related compound 10 , and the metal–ligand distances are characteristic of Fe II centers in pseudooctahedral environments 26. Upon oxidation, the metal–ligand (dppe, Cp*) bonds are lengthened.…”

“…It is useful to note that the use of t BuOK as a reducing agent has not been frequently reported. Indeed, it behaves as an efficient reducing reagent and is much cheaper and more convenient to use than cobaltocene, for instance 26,36. The redox potentials indicate that the reduction is not under thermodynamic control.…”

“…Finally, the synthesis and characterization of the three multicomponent molecular assemblies [Cp*(dppe)Fe=C=C=TTFMe 2 =CH–CH=TTFMe 2 =C=C=Fe(dppe)Cp*][PF 6 ] n ( 10 [PF 6 ] n , n = 0, 1, 2) has been reported 26. The experimental data were analyzed with the support of a theoretical study performed at the DFT level on the full structures.…”

“…With five components, namely, the two Fe centers, the two TTFMe 2 moieties, and the connecting organic bridge, the mixed‐valence 10 [PF 6 ] strongly differs from related mixed‐valence metal–organic bridge–metal systems and, to the best of our knowledge, is unprecedented. The involvement of all these components in the electron‐transfer process renders the usual Hush–Marcus two‐center model inappropriate 26,27…”

Binuclear Ruthenium Complexes with Benzo[1,2‐b;4,5‐b′]dithiophene Analogues as Bridge Ligands: Syntheses, Characterization and Notable Difference on Electronic Coupling

“…[1][2][3][4] Recently, numerous organic conjugative ligands and redox-active metal terminals were used to develop a type of "organometallic molecular wires" model. [9] As for the metal terminal groups, iron, [10] ruthenium, [7,8,11] osmium, [12] and molybdenum [13] units with different auxiliary ligands, such as cyclopentadienyl, bis(diphenylphosphino)ethane (dppe) are typically used because of their redox-active properties and electrochemical stability. [9] As for the metal terminal groups, iron, [10] ruthenium, [7,8,11] osmium, [12] and molybdenum [13] units with different auxiliary ligands, such as cyclopentadienyl, bis(diphenylphosphino)ethane (dppe) are typically used because of their redox-active properties and electrochemical stability.…”