Donor-acceptor substituted oligothiophenes: synthesis, spectroscopic and electrochemical properties

Seven new donor/acceptor oligothiophenes 1-2 were synthesized by Stille coupling in moderate to good yields. Compounds 1-2 were completely characterized by the usual spectroscopic methods. In agreement with the electrochemical and the spectroscopic studies for this compounds the new derivatives prepared, can find application for manufacturing new materials with strong non-linear optical (NLO) properties.Fundação para a Ciência e a Tecnologia (FCT

Synthesis of donor-acceptor substituted oligothiophenes by Stille coupling

A synthesis of donor-acceptor-substituted oligothiophenes by Stille coupling is described. The 5´-estanyl derivatives, readily prepared from 5-alkoxy- and 5-amino-2,2´-bithiophenes 7 were coupled with the appropriate aryl or heteroaryl bromides to give the title compounds.Fundação para a Ciência e Tecnologia. FEDER - POCTI/QUI/37816/2001

Effect of concentration of the diazoalcene molybdenum complex immobilized in ureasil matrix

The complex trans-[FMo(NNCHCHCHCH2CH3)(Ph2PCH2CH2PPh2)2][BPh4], was dispersed in a hybrid matrix synthesized by a sol-gel process. The host matrix of the so-called ureasil is a network of silica to which oligopolyoxyethylene chains [POE, (OCH2CH2)n] are grafted by means of urea cross-links. The free complex and sol-gel materials were characterized by thermal analysis (DSC), surface analysis (XPS) and spectroscopic methods (FT-IR and UV/Vis). The data gathered indicates that the molybdenum(IV) complex is immobilized in the host matrix, and it exhibits structural properties different from those of the free form. These differences could arise either from distortions caused by steric effects imposed by the structure of hybrid matrix or by interactions with the matrix. These materials shows potential applications in heterogeneous catalysis in mild conditions

Reactivity studies of thienyl and (oligo)thienylpyrroles

Currently, a variety of synthetic approaches to substituted pyrroles exist, although their synthesis, in general, remains challenging. Often, the yields are rather low and a significant number of by-products, such as undesired regioisomers, are obtained. Furthermore, pyrroles are susceptible to chemical degradation as they are rather easily oxidized; this further hampers their synthesis and especially their isolation and purification.1 The chemistry of thienylpyrroles is a very recent field in the chemistry of heterocyclic compounds. In the last few years, synthetic 2-thienylpyrrole derivatives have come in focus. However, even more than 60 years since the first 2-thienylpyrrole: bis-2-[5-(2-thienyl)pyrrole]azametine dihydrochloride) has been reported by Edward Knott2 at Kodak, the synthesis of functionalized thienyl and (oligo)thienylpyrroles remains challenging. Often, the yields are low and the regioselectivity is only modest.3 Before our recent work,3-4 only a few papers were published concerning the regioselectivity studies of 1-(alkyl)aryl-2-thienylpyrrole systems. Following our interest in the chemistry and optical applications of new functionalized systems bearing thiophene and pyrrole rings we have used heterocyclic systems 1 bearing pyrrole and thiophene rings (1, 2 or 3) as precursors for the synthesis of functionalyzed pyrrole derivatives. Compounds 1 have proved to be versatile substrates in several reactions (aromatic electrophilic substitutions: azo coupling, direct tricyanovinylation reaction, Vilsmeier-Haack formylation) and metalation followed by reaction with DMF, allowing the preparation of interesting new donor-acceptor substituted heterocyclic systems, selectively functionalized on the pyrrole 2 or on the thiophene 3 rings. Precursors 1 were prepared through a palladium-catalyzed decarboxylative cross-coupling reaction. The structures of the new compounds were unambiguously confirmed by their analytical and spectral data. Acknowledgments Thanks are due to the Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química - Universidade do Minho, Project PTDC/QUI/66251/2006 (FCOMP-01-0124-FEDER-007429), Project PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716) and a PhD grant to M. C. R. Castro (SFRH/BD/78037/2011). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT. References 1. Schmuch, C.; Rupprecht, D. Synthesis 2007, 3095. 2. Knott, E. B. J. Chem. Soc. 1947, 1196. 3. (a) Raposo, M. M. M. in Targets in Heterocyclic Systems: Chemistry and Properties, "Recent developments in the chemistry of 2-thienylpyrroles: synthesis, reactivity and applications", Attanasi, O. A.; Spinelli, D. Eds.; Royal Society of Chemistry: London, 2008, Vol. 11, pp 122-154. 4. (a) Raposo, M. M. M.; Sousa, A. M. R. C.; Fonseca, A. M. C.; Kirsch, G. Tetrahedron 2005, 61, 8249. (b) Raposo, M. M. M.; Sousa, A. M. R. C.; Kirsch, G.; Ferreira, F.; Belsley, M.; Matos Gomes, E.; Fonseca, A. M. C. Tetrahedron 2005, 61, 11991. (c) Raposo, M. M. M.; Sousa, A. M. R. C.; Fonseca, A. M. C.; Kirsch G. Tetrahedron 2006, 62, 3493. (d) Raposo, M. M. M.; Sousa, A. M. R. C.; Kirsch, G.; Cardoso, P.; Belsley, M.; Matos Gomes, E.; Fonseca, A. M. C. Org. Lett. 2006, 8, 3681. (e) Raposo, M. M. M.; Castro, M. C. R.; Schellenberg, P.; Fonseca, A. M. C.; Belsley, M. Tetrahedron 2011, 67, 5189

Synthesis of π-conjugated systems bearing thiophene and pyrrole heterocycles through palladium-catalyzed decarboxylative cross-coupling reaction

Thiophene and pyrrole moieties play important roles in synthetic and medicinal chemistry, as they are present in a large number of natural products and biologically active compounds. For this reason, amongst all five-membered aromatic heterocycles, molecules containing the pyrrole nucleus have attracted the greatest attention of researchers and have been studied in most detail. Especially, 2-aryl- and 2-heteroaryl-substituted pyrroles are of great interest to the pharmaceutical industry, for instance, as precursors in the synthesis of chemotherapeutics.1 Furthermore, synthetic pyrrole -containing derivatives (e.g. functionalized thienylpyrroles and 2,5-dithienylpyrroles) and -conjugated oligo- and polypyrrolic systems are of growing relevance in materials science, supramolecular chemistry, and nanotechnology. For example, they have found application in anion binding and cation coordination, conducting organic polymers, liquid crystals, and nonlinear optics.2 The wide array of interesting properties has inspired the development of several procedures for the preparation of differently substituted pyrroles. On the other hand, methods for the construction of 2-(2´-thienyl)pyrroles and (oligo)thienylpyrroles remains limited. Therefore the development of efficient methods for the synthesis of these compounds has become an important and topical area of heterocyclic chemistry. In our laboratories we have developed a convenient method for the syntheis of 1-alkyl(aryl)-2-thienylpyrroles, through the combination of the Friedel-Crafts and Lawesson reactions.3 The transition-metal-catalyzed decarboxylative cross-coupling has been recently utilized as a new synthetically useful tool for the preparation of heterocyclic systems.4 Having in mind our recent work and also our interest in the development of synthetic methodologies for the synthesis of novel heterocyclic systems we report in this communication the synthesis and the characterization of new -conjugated systems 1 bearing thiophene and pyrrole rings through palladium-catalyzed decarboxylative cross-coupling reaction between 1-methyl-1H-pyrrole-2-carboxylic acid 1 and thienyl bromides 2. Several reaction conditions (catalyst, solvent, additive, base, stoichiometry and temperature) were studied in order to obtain better yields for compounds 3. Some of the precursor thienyl bromides 2 were prepared through Suzuki coupling reaction. The new compounds were completely characterized by the usual spectroscopic techniques. Acknowledgments Thanks are due to the Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química - Universidade do Minho, Project PTDC/QUI/66251/2006 (FCOMP-01-0124-FEDER-007429), Project PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716) and a PhD grant to M. C. R. Castro (SFRH/BD/78037/2011). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT. References 1. Bellina, F.; Rossi, R. Tetrahedron 2006, 62, 7213. 2. (a) Raposo, M. M. M. in Targets in Heterocyclic Systems: Chemistry and Properties, "Recent developments in the chemistry of 2-thienylpyrroles: synthesis, reactivity and applications", Attanasi, O. A.; Spinelli, D. Eds.; Royal Society of Chemistry: London, 2008, Vol. 11, pp 122-154. (b) Raposo, M. M. M.; Sousa, A. M. R. C.; Kirsch, G.; Cardoso, P.; Belsley, M.; Matos Gomes, E.; Fonseca, A. M. C. Org. Lett. 2006, 8, 3681. (c) Raposo, M. M. M.; Castro, M. C. R.; Schellenberg, P.; Fonseca, A. M. C.; Belsley, M. Tetrahedron 2011, 67, 5189. 3. (a) Raposo, M. M. M.; Sampaio, A. M. B. A.; Kirsch, G. Synthesis 2005, 2, 199. (b) Raposo, M. M. M.; Sousa, A. M. R. C.; Fonseca, A. M. C.; Kirsch G. Tetrahedron 2006, 62, 3493. 4. Zhao, D.; You, J.; Hu, C. Chem. Eur. J. 2011, 17, 5466

Comparative study of the tarnishing resistance of several coloured base gold alloys

The stability of coloured gold alloys may be dependent on the environment that involves them. This paper is concerned with the effect of an artificial sweat solution in the stability of several gold base alloys with different colours. The changes in the samples physical properties, colour, brightness, and reflectance were measured for several periods of immersion. Two types of alloys (purple and blue coloured alloys) showed to be sensitive to the artificial sweat solution. The other tested alloys have a high resistance to tarnishing comparable with the results obtained for pure gold

Synthesis of formyl-thienylpyrroles : versatile building blocks for NLO materials

Several formyl-substituted 1-alkyl(aryl)-2-(2´-thienyl)pyrroles 3-7 were synthesized by functionalization of the pyrrole or thiophene ring of thienylpyrroles 2 using different methods: Vilsmeier formylation or metalation followed by reaction with DMF.Fundação para a Ciência e Tecnologi

Thienylpyrrole azo dyes: synthesis, solvatochromic and electrochemical properties

The synthesis and the evaluation of solvatochromic and electrochemical properties of new donor-acceptor-substituted thienylpyrrole azo dyes 3 are described. These derivatives exhibit dramatic changes in both their electronic and redox properties in comparison with thienylpyrroles 1. In agreement with the solvatochromic and electrochemical studies of push-pull derivatives 3 the new compounds prepared, may find application in the manufacture of new materials with notable non-linear optical properties.Fundação para a Ciència e Tecnologia - POCTI/QUI/37816/2001

Donor-acceptor substituted thienylpyrrole azo dyes: synthesis, solvatochromic and electrochemical properties

The synthesis of thienyl- substituted pyrrole azo dyes and their UV-visible, solvatochromic and electrochemical properties are described. In agreement with the solvatochromic data and also with the electrochemical study the new donor-acceptor systems synthesized could have applications in NLO.Fundação para a Ciência e Tecnologia (FCT

Highly efficient and thermally stable NLO organic materials based on pyrrole and thiophene heterocycles

A series of novel donor-acceptor chromophores designed to have good second order nonlinear optical responses has been synthesized and characterized. This series of compounds was designed to explore the consequence of using different electron accepting moieties which were linked through an arylthiophene bridge to a pyrrole heterocycle that plays the role of an auxiliary donor group. These new push-pull chromophores have been extensively characterized using cyclic voltammetry, thermogravimetric analysis and hyper-Rayleigh scattering (HRS) in solution. The measured molecular first hyperpolarizabilities and the observed electrochemical behavior showed that they were very sensitive to the acceptor strength of the acceptor moieties. Moreover, the combination of their good nonlinearity and high thermal stability make them good candidates for potential device applicationsThanks are due to the Fundacao para a Ciencia e Tecnologia (Portugal) and FEDER for financial support through the Centro de Quimica and Centro de Fisica-Universidade do Minho, Project PTDC/QUI/66251/2006 (FCOMP-01-0124-FEDER-007429), Project PTDC/CTM/105597/2008 with funding from COMPETE/FEDER and a research grant to M.C. R. Castro (UMINHO/BI/142/2009). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT