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Schmitt J.,CNRS Laboratory of Macromolecular Photochemistry and Engineering | Schmitt J.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Blanchard N.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Poly J.,CNRS Laboratory of Macromolecular Photochemistry and Engineering | Poly J.,CNRS Mulhouse Institute of Materials Science
Polymer Chemistry | Year: 2011

An original xanthate possessing a vinyl ester polymerizable function, namely vinyl 2-[(ethoxycarbonothioyl)sulfanyl]propanoate (Xa2), was synthesized. It was implemented as a chain transfer agent (CTA) to design branched polymers based on vinyl acetate (VAc) by self-condensing vinyl copolymerization (SCVC) by reversible addition-fragmentation chain transfer (RAFT). The branching density as well as the length of the branches were efficiently tuned by adjusting the total initial concentration of polymerizable functions C0 = [VAc]0 + [Xa2]0 and the ratio C0/[Xa2] 0. Additionally, Xa2 was also homopolymerized to provide hyperbranched oligomers. These precursors were used as multifunctional CTAs to control a subsequent polymerization of VAc, affording starlike poly(vinyl acetate)s (PVAcs). All the products were characterized by 1H NMR spectroscopy, quadruple detection size exclusion chromatography and differential scanning calorimetry. Reference samples consisted of linear PVAcs which were synthesized using a homologue non-polymerizable xanthate. As expected, the intrinsic viscosity and the glass transition temperature increased when either the number of branches or their length increased. © 2011 The Royal Society of Chemistry.


Duvanel G.,University of Geneva | Grilj J.,University of Geneva | Chaumeil H.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Jacques P.,Upper Alsace University | Vauthey E.,University of Geneva
Photochemical and Photobiological Sciences | Year: 2010

A series of pyridinium phenoxides that differ by the dihedral angle between the pyridinium and the phenoxide rings because of substituents with increasing steric encumbrance has been investigated by ultrafast spectroscopy. Like the related betaine-30, these molecules are characterised by a zwitterionic electronic ground state and a weakly polar S1 state. Their fluorescence lifetime was found to lie between 200 to 750 fs, decreasing with increasing dihedral angle, and increasing with solvent viscosity. This was assigned to a non-radiative deactivation of the emissive state coupled to a large amplitude motion involving the dihedral angle. The transient absorption spectra suggested that emission occurs from the Franck-Condon S1 state, which decays to a dark excited state, that itself most probably corresponds to the relaxed S1 state. Finally, this relaxed state decays to the vibrationally hot ground state through an intramolecular charge separation process with a time constant ranging between 0.4 and 3 ps, increasing with the dihedral angle and with the solvent relaxation time. These variations were discussed in terms of the Jortner-Bixon model of electron transfer, where the charge separation dynamics depends on both electronic coupling and solvent relaxation. The results suggested that charge separation slows down with increasing dihedral angle. © 2010 The Royal Society of Chemistry and Owner Societies.


Glaied O.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Delaite C.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Riess G.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory
Polymer Bulletin | Year: 2012

The synthesis of new poly(ε-caprolactone)(PCL)-b-poly(vinyl acetate)(PVAc) block copolymers was investigated using different combinations of click chemistry, reversible addition-fragmentation transfer (RAFT), and ring opening polymerization (ROP) techniques. Two approaches, "coupling" and "macroinitiator" routes were studied. For the coupling approach, a chain transfer agent comprising an azide function was synthesized and used as initiator for the VAc polymerization. PCL containing an alkyne termination was obtained from a bifunctional initiator bearing an alkyne function and an hydroxyl group. These two functionalized precursors, PVAc and PCL, were coupled by a 1,3 cyclo addition reaction "click chemistry" in order to obtain the corresponding block copolymer. For the macroinitiator approach, PCL-b-PVAc block copolymers were synthesized using a two-step procedure: at first, a PCL macroinitiator with a xanthate end group was prepared by coordinated anionic polymerization of ε-caprolactone; then, the RAFT polymerization of VAc was initiated from the PCL, for the preparation of PCL-b-PVAc block copolymers. Whatever the method used, no detectable quantities of unreacted PVAc or PCL were observed. 1H NMR and size exclusion chromatography analyses indicated successful synthesis of the block copolymers with well-defined structures. Graphical abstract: [Figure not available: see fulltext.] © 2011 Springer-Verlag.


Tehfe M.-A.,CNRS Mulhouse Institute of Materials Science | Lalevee J.,CNRS Mulhouse Institute of Materials Science | Morlet-Savary F.,CNRS Mulhouse Institute of Materials Science | Graff B.,CNRS Mulhouse Institute of Materials Science | And 2 more authors.
ACS Macro Letters | Year: 2012

A new organic photocatalyst (9,10-bis- [(triisopropylsilyl)ethynyl] anthracene, An-Si) is proposed here for the formation of free radicals under very soft irradiation conditions under air through a photoredox catalysis. It works according to an oxidative cycle that uses the combination of An-Si, a diphenyl iodonium salt along with a silane. This behavior is highlighted through an investigation of its excited state and redox properties. The different chemical intermediates are characterized by ESR experiments. In addition, the reversibility of the oxidation reaction of An-Si was investigated by cyclic voltammetry. This three-component system is able to promote the ring-opening photopolymerization of an epoxide as well as the free radical photopolymerization of an acrylate upon household LED bulb and Xe lamp exposure. Excellent polymerization profiles (mainly in ROP) are obtained. The specific properties of this catalyst are outlined. © 2011 American Chemical Society.


Goddard J.-P.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Ollivier C.,Paris-Sorbonne University | Fensterbank L.,Paris-Sorbonne University
Accounts of Chemical Research | Year: 2016

ConspectusRadical chemistry has witnessed over the last decades important advances that have positioned it as a methodology of choice in synthetic chemistry. A number of great attributes such as specific reactivities, the knowledge of the kinetics of most elementary processes, the functional group tolerance, and the possibility to operate cascade sequences are clearly responsible for this craze. Nevertheless, at the end of the last century, radical chemistry appeared plagued by several hurdles to overcome such as the use of environmentally problematic mediators or the impossibility of scale up. While the concept of photocatalysis was firmly established in the coordination chemistry community, its diffusion in organic synthetic chemistry remained sporadic for decades until the end of the 2000s with the breakthrough merging of organocatalysis and photocatalysis by the MacMillan group and contemporary reports by the groups of Yoon and Stephenson. Since then, photoredox catalysis has enjoyed particularly active and intense developments. It is now the topic of a still increasing number of publications featuring various applications from asymmetric synthesis, total synthesis of natural products, and polymerization to process (flow) chemistry.In this Account, we survey our own efforts in this domain, focusing on the elaboration of new photocatalytic pathways that could lead to the efficient generation of C-centered functionalized alkyl and aryl radicals. Both reductive and oxidative manifolds are accessible through photoredox catalysis, which has guided us along these lines in our projects.Thus, we studied the photocatalytic reduction of onium salts such as sulfoniums and iodoniums for the production of the elusive aryl radical intermediates. Progressing to more relevant chemistry for synthesis, we examined the cleavage of C-O and the C-Br bonds for the generation of alkyl C-centered radicals. Activated epoxides could serve as valuable substrates of a photocatalyzed variant of the Nugent-RajanBabu-Gansäuer homolytic cleavage of epoxides. Using imidazole based carbamates, we could also devise the first photocatalyzed Barton-McCombie deoxygenation reaction. Finally, bromophenylacetate can be reduced using the [Au2(μ-dppm)2]Cl2 photocatalyst under UVA or visible-light. This was used for the initiation of the controlled atom transfer radical polymerization of methacrylates and acrylates in solution or laminate.Our next endeavors concerned the photocatalyzed oxidation of stabilized carbanions such as enolates of 1,3-dicarbonyl substrates, trifluoroborates, and more extensively bis-catecholato silicates. Because of their low oxidation potentials, the later have proved to be exquisite sources of radical entities, which can be engaged in diverse intermolecular reactions such as vinylation, alkynylation, and conjugate additions. The bis-catecholato silicates were also shown to behave as excellent partners of dual photoredox-nickel catalysis leading in an expeditious manner to libraries of cross coupling products. © 2016 American Chemical Society.


Calvet G.,CNRS Orsay Institute of Molecular Chemistry | Coote S.C.,CNRS Orsay Institute of Molecular Chemistry | Blanchard N.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Kouklovsky C.,CNRS Orsay Institute of Molecular Chemistry
Tetrahedron | Year: 2010

α-Acyloxynitroso derivatives are a class of heterodienophiles leading to valuable 3,6-dihydro-1,2-oxazines or the corresponding aminoalcohols in good yields. The discovery that a β-oxygenated moiety led to a domino [4+2] cycloaddition/σN-O bond cleavage in the presence of a catalytic amount of Lewis acid was investigated in detail, through kinetic profiling of the reaction both in the absence and presence of a promoter. These studies showed that the role of the Lewis acid was to accelerate the σN-O bond cleavage thereby promoting a highly reproducible sequence. In addition, our preliminary results on an asymmetric version of this domino sequence are reported. © 2010 Elsevier Ltd. All rights reserved.


Corce V.,Paris-Sorbonne University | Chamoreau L.-M.,Paris-Sorbonne University | Derat E.,Paris-Sorbonne University | Goddard J.-P.,Paris-Sorbonne University | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2015

This works introduces hypervalent bis-catecholato silicon compounds as versatile sources of alkyl radicals upon visible-light photocatalysis. Using Ir[(dF(CF3)ppy)2(bpy)](PF6) (dF(CF3)ppy=2-(2,4-difluorophenyl)-5-trifluoromethylpyridine, bpy=bipyridine) as catalytic photooxidant, a series of alkyl radicals, including highly reactive primary ones can be generated and engaged in various intermolecular homolytic reactions. Based on cyclic voltammetry, Stern-Volmer studies, and supported by calculations, a mechanism involving a single-electron transfer from the silicate to the photoactivated iridium complex has been proposed. This oxidative photocatalyzed process can be efficiently merged with nickel-catalyzed Csp2-Csp3 cross-coupling reactions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Tahtaoui C.,ARPIDA AG | Demailly A.,ARPIDA AG | Guidemann C.,ARPIDA AG | Joyeux C.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Schneider P.,ARPIDA AG
Journal of Organic Chemistry | Year: 2010

Figure presented Both enantiomers of the DHFR inhibitor iclaprim (R)-1 and (S)-1 were synthesized from the cyclopropyl homoallyl alcohols (R)-6 and (S)-6, respectively. As key steps these transformations include a Mitsunobu reaction and the formation of the diaminopyrimidine unit prior to a novel cyclization procedure to obtain the desired chromene heterocycle. The moderate enantioselectivity of the products (R)-1 and (S)-1 is related to the Mitsunobu reaction, which unfortunately did not proceed with complete inversion of configuration. © 2010 American Chemical Society.


Telitel S.,Upper Alsace University | Vallet A.-L.,French National Center for Scientific Research | Schweizer S.,CNRS Organic, Bioorganic and Macromolecular Chemistry Laboratory | Delpech B.,French National Center for Scientific Research | And 7 more authors.
Journal of the American Chemical Society | Year: 2013

The B-S bond in N-heterocyclic carbene (NHC)-boryl sulfides can be cleaved homolytically to NHC-boryl or NHC-thioboryl and thiyl radicals using light, either directly around 300 nm or with a sensitizer at a longer wavelength (>340 nm). In contrast, the electrochemical reductive cleavage of the B-S bond is difficult. This easy photolytic cleavage makes the NHC-boryl sulfides good type I photopolymerization initiators for the polymerization of acrylates under air. © 2013 American Chemical Society.


Tehfe M.-A.,CNRS Mulhouse Institute of Materials Science | Lalevee J.,CNRS Mulhouse Institute of Materials Science | Morlet-Savary F.,CNRS Mulhouse Institute of Materials Science | Graff B.,CNRS Mulhouse Institute of Materials Science | And 2 more authors.
Macromolecules | Year: 2012

New organic photocatalysts derived from pyrene, anthracene, naphthacene, and pentacene are presented here for the formation of free radicals through a photoredox catalysis. These OPCs can work according to an oxidative cycle in a three component system in combination with diphenyl iodonium salt and a silane or in a reductive cycle in combination with amine and alkyl halide. This OPC behavior is highlighted through an investigation of the associated excited state and redox properties. The free radicals generated are characterized by ESR or photolysis experiments. Upon household LED bulb or Xe lamp exposure, the oxidative three-component system is able to promote the ring-opening polymerization ROP of an epoxide whereas the reductive three-component system is very efficient to initiate the free radical photopolymerization FRP of an acrylate. This ability of OPCs to initiate different polymerization reactions (ROP and FRP) is clearly an outstanding property. © 2012 American Chemical Society.

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