Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

International audienceWittig reaction between the in situ generated [2,6-diphenyl-4H-pyran-4-yl phosphorane and methyl 4-formylbenzoate afforded the methyl 4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]benzoate precursor 2 in 75% yield. The anisyl and ferrocenyl adducts of methylenepyran-containing β-diketones 3 and 4, respectively, were prepared from the base-catalyzed Claisen condensation reaction between precursor 2 and 4-methoxyacetophenone or acetylferrocene, using t-BuO−K+ as basic initiator. Both β-diketones 3 and 4 were isolated as an orange and dark-red crystalline solids in 50% yield, respectively. The acetyl derivative 6, 1-acetyl-1′-methylenepyranyl-ferrocene, was synthesized following a classical Friedel-Crafts acylation reaction of the parent ferrocenylmethylenepyran 5, and isolated in 61% yield as a red microcrystalline powder. The condensation reaction between the electron-rich acetyl complex 6 and acetyl acetate, using lithium diisopropylamide as the active base initiator, provided the ferrocenylmethylenepyran-containing β-diketone, 1-(1,3-dioxobutyl)-1′-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl] ferrocene 7, isolated in 20% yield as an orange powder. The composition and identity of the new compounds 2-4, 6 and 7 are supported by elemental analysis, FT-IR, one- and two-dimensional 1H and 13C NMR spectral data and mass spectrometry. Additionally, the molecular structures of compounds 2, 4 and 6 were ascertained by single-crystal X-ray diffraction study. FT-IR and NMR spectral data indicate that both β-diketones 3 and 4 do solely exist as their keto-enol tautomeric form in solution and in the solid state, whereas a mixture of keto-enol and β-diketone tautomers in a 73:27 spectroscopic ratio was observed for 7. In the three cases, enolization takes place exclusively away from the anisyl or ferrocenyl group with formation of a six-membered pseudo-aromatic keto-enol ring, confirmed by the crystal structure of 4. Cyclic voltammetric measurements revealed that all the compounds undergo a single one-electron oxidation, localized presumably at the methylenepyran unit. This first oxidation generates a radical cation that undergoes an intermolecular C-C bond coupling to form the corresponding dimer. Anodically shifted to the first oxidation, cyclovoltammogram of 4 exhibits one reversible two-electron oxidation while that of 6 and 7 present two successive reversible one-electron oxidations, attributed in the three cases to the ferrocenyl fragment of the dimer

Tripodal molecules with triphenylamine core, diazine peripheral groups and extended π-conjugated linkers

International audienceA series of five octupolar molecules with central triphenylamine donor and peripheral diazine electron-withdrawing groups has been prepared. These structures possess extended π-spacer comprising multiple bonds in a combination with 1,4-phenylene and 2,5-thienylene subunits. Starting from tris(4-ethynylphenyl)amine, the key step in the preparation of the chromophores involves triple Sonogashira cross-coupling reaction. The photophysical properties of the compounds are described. A strong positive emission solvatochromism, typical for dyes featuring Intramolecular Charge Transfer (ICT), is observed, two-photon absorption (2PA) properties were also measured. Linear and nonlinear optical properties as well as electronic properties measured by cyclic voltametry and supported by DFT calculation were used to elucidate structure-property relationship

Apports de nouveaux systèmes bimétalliques dans les réactions d'activation originales de molécules organiques insaturées

Les dérivés métalliques à environnement soufre sont impliqués dans de nombreux processus industriels et biologiques. Afin d'évaluer l'apport que peuvent avoir des systèmes bimétalliques thiolatoponthes du molybdène {Mo2Cp2)(u-SMe)n} (n= 2,3) dans de tels processus, l'étude de leur réactivité vis à vis de divers substrats, en particulier insaturés, a été entreprise en présence d'alcyne. Des complexes possédant un ligand alcyne, ponte entre les deux métaux, ont été isolés et caractérisés. La réactivité de ces composés vis à vis de substrats (RNC, RCCH, CS2) a été étudiée et l'insertion de l'alcyne dans une liaison métal-soufre a été systématiquement observée.L'isomérisation alcyne-vinylidène en alkyle a été mise en évidence et la transformation du ligand vinylidène en alkyle a été réalisée, sous action successive d'ions hydrures et de protons. La réactivité de complexes nitrile et chloroponte du molybdène avec NABH4, a également été développée. Le transfert d'un hydrure sur l'atome de carbone du ligand acétonitrile et/ou la substitution des ligands acetonitrile par un ion BH4- a été observé, conduisant à des ligands azavinylidène, borohydrure, borane ou hydrure. Enfin, les récations de complexes [Mo2Cp2(u-SMe)3(L)2]+ où L est un ligand carbonyle ou isocyanure, vis à vis de nucléophiles et de bases, a montré que le site electrophile dépend de la nature du ligand L. Des produits originaux résultant d'une réaction de couplage C-C entre le ligand Cp et l'un des ligands isocyanure et de couplage C-N entre les deux ligands isocyanure ont également été décrits. La variété des complexes obtenus montre la capacité réactive du système étudié.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Protonable pyrimidine derivative for white light emission

International audienceWhite photoluminescence both in soln. and the solid-state was obtained by the controlled protonation of a blue emitting 4,6-bis(arylvinyl)pyrimidine, which resulted in the formation of an orange emissive acidified form. This dye has potential applications in the fabrication of white OLEDs based on only one material

Methylation sites in tris(μ-thiolato)dimolybdenum(III) complexes

International audienceAttempts at methylating cis-[Mo2Cp2(μ-SMe)3L2](BF4) [Cp = η5-C5H5; L = CO (1a) CNxyl (1b), CNBut (1c), NCMe (1d)] with methyl triflate gave the corresponding thioether-bridged cations [Mo2Cp2(μ-SMe)2(μ-SMe2)L2]2+ (42+), except in the case of 1a which did not react at room temperature. The electronic properties of the ancillary ligands L thus have a crucial influence on the course of this reaction. The dimeric compounds [Mo2Cp2(μ-SMe)3(CNBut)(CN)] (2) and [Mo2Cp2(μ-SMe)3{μ-η1-Ndouble bond; length as m-dashC(CH3)CH2CN}] (3), which potentially offer the alternatives of S- or N-methylation, reacted with methylating agents to give mainly the S-methylated derivatives 5 and 7. Only in the case of the nucleophilic reactant 2 was N-methylation also observed and isomer 6 was obtained as a minor product together with 5. New complexes have been completely characterised by multinuclear NMR, IR and elemental analysis, supplemented for 5 by X-ray diffraction study at 100 K

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

Activation of terminal alkynes at the sulfur-rich bimetallic site [MoIII2Cp2(μ-SMe)3]+: Alkyne-vinylidene conversion and C-S and C-C couplings promoted by addition of unsaturated substrates (RC≡CH, RN≡C, S=C=S).

cited By 33International audienceReactions of the bis(nitrile) compound [Mo2Cp2 (MeCN)2(μ-SMe)3](BF4) (1) with terminal alkynes in a 1:1 ratio in dichloromethane at room temperature led to the alkyne adduct [Mo2Cp2(μ-SMe)3(RCCH)] (BF4) (2: R = Tol (2a), Ph (2b), CH3C=CH2 (2c), nPr (2d), CO2Me (2e), CF3 (2f)). Compounds 2a-d were readily deprotonated with Et3N to give neutral acetylide derivatives [Mo2Cp2(μ-η1:η2- C≡CR)(μ-SMe)3] (3). Protonation of 3 afforded exclusively the vinylidene complexes [Mo2Cp2(μ-η1: η2-C=CHR) (μ-SMe)3](BF3) (4). Reaction of 1 with an excess of terminal alkyne RCCH in dichloromethane gave either the six-membered metallacycle compounds [Mo2Cp2(μ- η2:η4-CR=CHCR=CHSMe)(μ-SMe)2] (BF4) (5) or the S-methylthiophenium derivatives [Mo2Cp2(μ-η2:η4- C4H2R2SMe)(μ-SMe)2] (BF4) (6), depending on the nature of the R groups. Further reactions of the alkyne adducts 2 with isocyanide and carbon disulfide led to the vinyl-thioether complexes [Mo2Cp2(μ- η1:η3-CR=CR′-SMe)-(μSMe)2 (RNC)](BF4) (7, 8) and to their CS2 adducts [Mo2Cp2(S2C-CR′=CRSMe)(μ- SMe)2]-(BF4) (9, 10), which arise from regioselective C-S coupling. A mechanism is proposed for the formation of the cyclic thiometalla compounds 5, 9, and 10 and of the thiophenium species 6 which assigns a key intermediate role to vinyl-thioether species. The molecular structures of 3a, 4b, and 7a have been established by X-ray diffraction studies

Dipolar and V-​shaped structures incorporating methylenepyran and diazine fragments

International audienceThirteen novel dipolar and V-​shaped chromophores with pyranylidene electron-​donating part, diazine electron-​withdrawing part and various π-​linkers were synthesized. The extent of intramol. charge transfer, structure-​property relationships and optical properties were further investigated by UV​/Vis absorption, electrochem., and DFT calcns

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