Two Metals Are Better Than One in the Gold Catalyzed Oxidative Heteroarylation of Alkenes

We present a detailed study of the mechanism for oxidative heteroarylation, based on DFT calculations and experimental observations. We propose binuclear Au(II)–Au(II) complexes to be key intermediates in the mechanism for gold catalyzed oxidative heteroarylation. The reaction is thought to proceed via a gold redox cycle involving initial oxidation of Au(I) to binuclear Au(II)–Au(II) complexes by Selectfluor, followed by heteroauration and reductive elimination. While it is tempting to invoke a transmetalation/reductive elimination mechanism similar to that proposed for other transition metal complexes, experimental and DFT studies suggest that the key C–C bond forming reaction occurs via a bimolecular reductive elimination process (devoid of transmetalation). In addition, the stereochemistry of the elimination step was determined experimentally to proceed with complete retention. Ligand and halide effects played an important role in the development and optimization of the catalyst; our data provides an explanation for the ligand effects observed experimentally, useful for future catalyst development. Cyclic voltammetry data is presented that supports redox synergy of the Au···Au aurophilic interaction. The monometallic reductive elimination from mononuclear Au(III) complexes is also studied from which we can predict a ~ 15 kcal/mol advantage for bimetallic reductive elimination

Applying direct heteroarylation synthesis to evaluate organic dyes as the core component in PDI-based molecular materials for fullerene-free organic solar cells

Direct heteroarylation has emerged as a versatile and powerful tool to access π-conjugated materials through atom-economical Pd-catalyzed carbon–carbon bond forming reactions. Employing this synthetic protocol has enabled the facile evaluation of a series of organic dyes in a PDI-dye-PDI framework. Material properties are largely dictated by the PDI components, but the incorporation of either thienoisoindigo, diketopyrrolopyrrole or isoindigo has been shown to influence the ionization potential and absorption profiles of the final materials. Solution-processable organic solar cell devices were fabricated to investigate the influence of the different dye cores on photovoltaic performance when paired with the donor polymer PTB7-Th. It was found that the diketopyrrolopyrrole-based material out-performed the other organic dyes, demonstrating energy losses of less than 0.6 eV, promising efficiencies when cast from non-halogenated solvents and the ability to dictate self-assembly induced by small volume fractions of the high-boiling solvent additive 1,8-diiodooctane to reach best device efficiencies of 4.1%

Perfluorocyclohexene bridges in inverse DiArylEthenes: synthesis through Pd-catalysed C-H bond activation, experimental and theoretical studies on their photoreactivity.

International audienceThe palladium-catalysed direct di-heteroarylation of 1,2-dichloroperfluorocyclohexene with a variety of heteroarenes gives rise in to a new family of 1,2-di(heteroaryl)perfluorocyclohexenes. These derivatives do not exhibit photoreactivity and this unexpected outcome is explained by calculations demonstrating the lack of reactive isomers

Synthesis of heteroarenes dyads from heteroarenes and heteroarylsulfonyl chlorides via Pd-catalyzed desulfitative C-H bond heteroarylations

International audienceWe report herein on the palladium-catalyzed direct heteroarylation of heteroarenes (e.g., pyrroles, furans, and thiophenes) in which heteroarylsulfonyl chlorides are used as coupling partners through a desulfitative cross-coupling. These C-H bond functionalizations occurred at the α-position in the case of pyrrole and furan derivs., while in the case of thiophenes the C-H bonds at the β-position have been heteroarylated. This methodol. represents a very simple route to heteroaryl dyads. Moreover, some examples of heteroaryl triads have been synthesized via iterative C-H bond arylations

Highly selective electrochemical hydrogenation of alkynes: Rapid construction of mechanochromic materials

Electrochemical hydrogenation has emerged as an environmentally benign and operationally simple alternative to traditional catalytic reduction of organic compounds. Here, we have disclosed for the first time the electrochemical hydrogenation of alkynes to a library of synthetically important Z-alkenes under mild conditions with great selectivity and efficiency. The deuterium and control experiments of electrochemical hydrogenation suggest that the hydrogen source comes from the solvent, supporting electrolyte, and base. The scanning electron microscopy and x-ray diffraction experiments demonstrate that palladium nanoparticles generated in the electrochemical reaction act as a chemisorbed hydrogen carrier. Moreover, complete reduction of alkynes to saturated alkanes can be achieved through slightly modified conditions. Furthermore, a series of novel mechanofluorochromic materials have been efficiently constructed with this protocol that showed blue-shifted mechanochromism. This discovery represents the first example of cis-olefins-based organic mechanochromic materials

Synthesis of pi-conjugated systems bearing thiophene and pyrrole heterocycles through palladium catalyzed cross-coupling reactions.

A series of thienylpyrroles and bithienylpyrroles together with their formyl derivatives 5aed were synthesized using commercially or readily available coupling components, through three different palladium catalyzed cross-coupling reactions (Suzuki-Miyaura, Stille and decarboxylative coupling). The synthesis of compounds 5 via the Suzuki-Miyaura reaction produced the title compounds in better yields than the other coupling reactions, while, decarboxylative coupling resulted in the lower yields. UV-visible and 1H NMR studies confirm the existence of significant intramolecular charge transfer (ICT) from the donor pyrrole heterocycle to the acceptor group and a high polarizability of the whole pi-conjugated systems. Together these characteristics indicate their strong potential as versatile precursors for the preparation of push-pull heterocyclic compounds for optical applications.The authors thank the Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química – Universidade do Minho, Projects PTDC/QUI/66251/2006 (FCOMP-01-0124-FEDER-007429), CQ/UM PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302) 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, with funds from FCT

Synthesis of α-functionalized α-indol-3-yl carbonyls through direct SN reactions of indol-3-yl α-acyloins

A new and efficient synthesis of α-functionalized α-indol-3-yl ketones from easily available indolyl α-acyloins is reported. This process, catalyzed by Brønsted or Lewis acids, involves an uncommon direct nucleophilic substitution reaction of a secondary α-carbonyl-substituted hydroxyl group. The described methodology allows the introduction of a variety of nucleophiles such as (hetero)arenes, thiophenols, nitroanilines and 1,3-dicarbonyl derivatives. The synthesized α-indol-3-yl carbonyl compounds are important synthetic targets also useful for accessing functionalized tryptophols and furan-3-yl indoles.Ministerio de Economía y Competitividad (MINECO) (CTQ2013-48937-C2-1-P) and Junta de Castilla y León and FEDER (BU237U13 and BU076U16

Direct (Hetero)Arylation Polymerization of a Spirobifluorene and a Dithienyl-Diketopyrrolopyrrole Derivative: New Donor Polymers for Organic Solar Cells

The synthesis and preliminary evaluation as donor material for organic photovoltaics of the poly(diketopyrrolopyrrole-spirobifluorene) (PDPPSBF) is reported herein. Prepared via homogeneous and heterogeneous direct (hetero)arylation polymerization (DHAP), through the use of different catalytic systems, conjugated polymers with comparable molecular weights were obtained. The polymers exhibited strong optical absorption out to 700 nm as thin-films and had appropriate electronic energy levels for use as a donor with PC70BM. Bulk heterojunction solar cells were fabricated giving power conversion efficiencies above 4%. These results reveal the potential of such polymers prepared in only three steps from affordable and commercially available starting material

Impact of Backbone fluorination on -conjugated polymers in organic photovoltaic devices: a review

Solution-processed bulk heterojunction solar cells have experienced a remarkable acceleration in performances in the last two decades, reaching power conversion efficiencies above 10%. This impressive progress is the outcome of a simultaneous development of more advanced device architectures and of optimized semiconducting polymers. Several chemical approaches have been developed to fine-tune the optoelectronics and structural polymer parameters required to reach high efficiencies. Fluorination of the conjugated polymer backbone has appeared recently to be an especially promising approach for the development of efficient semiconducting polymers. As a matter of fact, most currently best-performing semiconducting polymers are using fluorine atoms in their conjugated backbone. In this review, we attempt to give an up-to-date overview of the latest results achieved on fluorinated polymers for solar cells and to highlight general polymer properties’ evolution trends related to the fluorination of their conjugated backbone

Recent advances in catalysis using transition metals-bounding organic ligands assisted by ultrasound and/or microwave

Usually, in organic and organometallic synthesis an external conventional heat source is applied to carry out a chemical reaction at high temperature. Nonetheless, these conventional heating systems have some disadvantages as the heterogeneous heating causing a low reproducibility of the results and extended reaction times. A promising alternative is the use of microwave (MW) and ultrasound (US) energy. The use of these techniques has led to considerable advantages as better homogeneity in temperature and very short reaction time. By virtue of the effects mentioned above, the MW and US irradiation constitutes a convenient way to accelerate and improve a great number of organic and organometallic reactions. In this paper, we have compiled an overview developed during the last decade in the synthesis of such catalysts and organic transformations assisted by both techniques mentioned above.Fil: Álvarez, Mónica Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; ArgentinaFil: Domini, Claudia Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; ArgentinaFil: Silbestri, Gustavo Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentin