Electron transfer properties of mono- and diferrocenyl based Cu complexes attached as self-assembled monolayers on gold electrodes by "self-induced" electroclick

International audienceTwo new Cu complexes bearing a 6-ethynyl bis-(methyl-pyridyl) amine (6eBMPA) moiety, as an electroclickable function linked to a ferrocenyl-based triazolyl arm (ligands 3 and 4) have been synthetized and characterized by UV-Visible, EPR spectroscopies and cyclic voltammetry in acetonitrile. Two different spacer groups between the terminal ferrocene and the triazolyl group were inserted: an hexyl chain in the case of the complex Cu-3, an ethenyl-bridged diferrocenyl system for the complex Cu-4. The monoelectronic oxidation of the diferrocenyl species yields a stable mixed-valence complex. NIR-Visible spectroscopic studies show a moderate interaction between ferrocenyl units (class II according to the Robin-Day classification). The immobilization of these systems as SAMs on an azidoundecanethiol modified gold electrode has been successfully operated by using the "self-induced electroclick" procedure. The voltammetric characterization of the surface-tagged Cu complexes indicates that good surface coverage was achieved, with moderately fast electron-transfer reaction between the electrode and the redox active immobilized systems (k0(Cu) = 2-4 s−1, k0(Fc) = 20-90 s−1). Remarkably, the rate of charge transport is significantly controlled by the nature of the spacer on the ferrocenyl triazole arm

The synthesis of flexible tetrapyridylethanes from pyridylpyrylium dications

International audienceNew tetrapyridylethanes can be prepd. as new tetradentate pyridine ligands via the aminolysis reaction of pyrylium dications, using an original oxidn. process of phenylpyridyl methylenepyrans. Crystal structure anal., and spectroscopic and electrochem. studies show the possibility for using these new ligands in coordination chem

Selective reactivity of diamino Fischer-type carbene complexes towards 2,6-disubstituted and 2,4,6-trisubstituted pyrylium salts and 2,4,6-trichloro-1,3,5-triazine

International audienc

Insights into the radical-radical and radical-substrate dimerization processes for substituted phenylmethylenepyrans

International audienceThe electrochemically-induced CC bond making/breaking for six differently R-substituted phenylmethylenepyrans has been investigated by voltammetry in organic media. All compounds display an irreversible oxidation peak whose potential is fully dependent on the electrophilic property of the substituent R. The electrochemical oxidation yields bis-pyrylium compounds by σ-σ CC bond formation. The initial methylenepyrans are recovered by cleavage of the CC bond through electrochemical reduction of the bis-pyrylium species. According to the voltammetric analysis, the mechanistic pathway, radical-radical or radical-substrate, for the intermolecular dimerization is fully R-dependent. Electronic structure calculations show that the spin population in the radical cation and the strength of the σ-σ CC bond in the dimer strongly depend on the nature of R. In addition, low-temperature electrochemical voltammetry (175 K), and room-temperature high scan rate cyclic voltammetry have been used to unravel the kinetics of the CC bond formation

Ferrocenyl and pyridyl methylenepyrans as potential precursors of organometallic electron-rich extended bipyrans: Synthesis, characterization and crystal structure

International audienceFerrocenyl and pyridyl methylenepyrans were obtained from a Wittig reaction between a pyran phosphorane and ferrocenyl or pyridyl-aldehydes. The nucleophilic nature of the exocyclic C-C bond allowed the formylation of these compounds by a Vilsmeier type reaction. All the new products were characterized by IR spectroscopy, 1H and 13C NMR spectroscopy, mass spectroscopy and (or) elemental analysis. Electrochemistry of representative compounds 2, 10 and 13 was undertaken. In addition, a crystal structure of the ferrocenylpyranylidene aldehyde 5 was described, and the pyrylium character of this compound was specified

Reversible redox switching of chromophoric phenylmethylenepyrans by carbon-carbon bond making/breaking

International audienceElectrochromic organic systems that can undergo substantial variation of their optical properties upon electron stimulus are of high interest for the development of functional materials. In particular, devices based on radical dimerization are appropriate because of the effectiveness and speed of the carbon-carbon bond making/breaking. Phenylmethylenepyrans are organic chromophores which are well suited for such purpose since their oxidation leads to the reversible formation of bispyrylium species by radical dimerization. In this paper, we show that the redox and spectroscopic properties of phenylmethylenepyrans can be modulated by adequate variation of the substituting group on the para position of the phenyl moiety, as supported by DFT calculations. This redox switching is reversible over several cycles and is accompanied by a significant modification of the UV-Vis spectrum of the chromophore, as shown by time-resolved spectroelectrochemistry in thin layer conditions

Diferrocenylbispyrylium Salts and Electron-Rich Diferrocenylbispyran from Oxidative Coupling of Ferrocenylpyran. Induced Electron Transfer C-C Bond Making/Breaking Involving a Metallocenyl Radical Intermediate

International audienceElectrochemical or chemical dimerization of electronrich ferrocenylmethylenepyran 1 gave the first dimetallocenylbispyrylium salt 2 known today, through a reverse process that implies reductive C-C bond breaking. Deprotonation of the bispyrylium salt 2 afforded extended electron-rich diferrocenyl bispyran 3, which was subsequently reversibly oxidized to diferrocenyl bispyrylium salt 4. This study constitutes a new system in which two ox/red sequences of different nature were separated by proton/deprotonation steps

Methylenepyran unsaturated Fischer carbene complexes from γ-methylpyrylium salts and alkynylcarbenes. Evolution to spiro-pyran-cyclopentenone compounds

International audiencePush-pull methylenepyran compounds 3 containing ferrocenyl or aryl groups are synthesized from reaction of condensation between γ-methyl-pyrylium salts 1 as precursors of γ-methylenepyrans and alkynylcarbene complexes 2 as Michaël-type acceptors. The new carbenes 3 evolve in CH2Cl2 solution at room temperature to provide spiro-fused-pyran-cyclopentenenone 4 and polysubstituted cyclopentenones 5

Synthesis and characterization of novel nitroxide organometallic Fischer-type carbene complexes

International audienceReactions of 4-amino TEMPO with alkynylmethoxy Fischer type carbene complexes lead to unknown transition organometallic nitroxide spin labels. According to the temperature and the nature of the aromatic group of the initial alkynyl carbene, Michael adducts and aminolysis products were obtained in various proportions. The reaction was extended to ferrocenyl carbene complexes to obtain novel organometallic spin systems containing two kinds of redox units. Their constitution is in agreement with IR, elemental analysis and mass spectrometry. Single X-ray diffraction has confirmed the molecular structure of the complexes and has showed the existence of intra and intermolecular hydrogen bonds. These air-stable paramagnetic carbenes have interesting redox behaviours and paramagnetic properties

Differocenyl Pyrrylium Salts and Electron Rich Bispyran from Oxidative Coupling of Ferrocenylpyran. Example of Redox Systems Switched by Proton transfer

International audienceElectro or chemical oxidation of ferrocenylmethylenepyran gave an ethanediferrocenylbispyrylium salt through the dimerization of a ferrocenylpyran radical-cation (C-C bond making). Electro or chemical reduction gave back the ferrocenylmethylenepyran (C-C bond breaking). This electrochemical reverse system constitutes an example of C-C bond making-breaking process in a metallocenyl series with rather high stability. DFT calculations and electrochemical studies were carried out in order to determine the electronic structure of the radical cation intermediate, the role of the ferrocenyl groups and the mechanism of the C-C bond making and C-C bond breaking processes. Reversible deprotonation of the ethanediferrocenylbispyrylium salt afforded an extended diferrocenylbismethylenepyran, which was subsequently reversibly oxidized to an ethenediferrocenylbispyrylium salt. X-Ray crystallographic data of diferrocenylbismethylenepyran and ethenediferrocenylbispyrylium salt allowed to determine the molecular movements, which come with the electron transfer (ET). A comparison with the behavior of the corresponding isoelectronic bisdithiafulvenes (extended TTF) and bisdithiolium salts was made