9 research outputs found

    Ambiphilic Ligands and Metal - Lewis Acid Cooperativity

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    Cette thĂšse porte sur l'Ă©tude de la coopĂ©rativitĂ© mĂ©tal/acide de Lewis. L'or se distingue des autres mĂ©taux de transitions par une rĂ©ticence Ă  s'engager dans les Ă©tapes Ă©lĂ©mentaires classiquement rencontrĂ©es en chimie organomĂ©tallique. Ce projet de recherche repose sur la coordination de l'or par des ligands ambiphiles permettant l'installation d'un acide de Lewis dans la sphĂšre de coordination. L'objectif ici est de tirer profit de la proximitĂ© de l'accepteur pour exalter la rĂ©activitĂ© de l'or et rĂ©aliser des transformations initialement dĂ©favorables. Le premier chapitre aborde de maniĂšre trĂšs gĂ©nĂ©rale l'Ă©tat de l'art de la chimie organomĂ©tallique de l'or. Une attention particuliĂšre est portĂ©e aux limitations gĂ©nĂ©rĂ©es par une difficultĂ© intrinsĂšque de ce mĂ©tal Ă  accĂ©der Ă  de hauts degrĂ©s d'oxydations. La coordination des ligands ambiphiles sur l'or y est introduite dans un second temps. La relation entre les divers modes de coordinations adoptĂ©s et la rĂ©activitĂ© des complexes rĂ©sultant a Ă©tĂ© mise en avant. Le deuxiĂšme chapitre est consacrĂ© Ă  la synthĂšse de nouveaux complexes d'or PB-Au(I)-R comportant un co-ligand organique. Ces derniers ont Ă©tĂ© obtenu depuis des prĂ©curseurs aryle, mĂ©thyle et trifluoromĂ©thyle d'Au(I) par coordination d'une phosphine borane rĂ©cemment dĂ©crite par l'Ă©quipe et prĂ©sentant un fragment borane hautement acide de Lewis. La prĂ©sence d'une interaction datives de l'or vers le bore a pu ĂȘtre Ă©tabli. L'Ă©valuation de la force de l'interaction Au→B a notamment permis de discuter le caractĂšre sigma-accepteur du nouveau ligand. L'addition oxydante de divers Ă©lectrophiles a ensuite Ă©tĂ© Ă©tudiĂ©e. Lors l'exploration de la rĂ©activitĂ© des complexes PB-Au(I)-R (R = vinyle, acĂ©tylĂšnyle), une rĂ©action de 1,1-phosphaboration stĂ©rĂ©o- et rĂ©giosĂ©lective du groupement insaturĂ© a Ă©tĂ© dĂ©couverte et fera l'objet d'un troisiĂšme chapitre. Des complexes zwittĂ©rioniques issus de l'abstraction du groupement organique de l'or vers le bore ont Ă©tĂ© identifiĂ©s comme intermĂ©diaire clĂ© de la transformation. Le mĂ©canisme de la rĂ©action a fait l'objet d'une Ă©tude expĂ©rimentale et thĂ©orique mettant en Ă©vidence une action concertĂ©e du bore et de l'or. Enfin, il a Ă©tĂ© dĂ©montrĂ© dans un dernier chapitre que la coordination des mono-phosphines boranes sur les complexes d'Au(III) favorise grandement l'Ă©limination rĂ©ductrice C(sp3)-C(sp3) connue pour ĂȘtre difficile. Des Ă©tudes cinĂ©tiques montrent un impact de la prĂ©sence de l'acide de Lewis. L'Ă©tude par DFT du mĂ©canisme soutient la participation du borane des ligands ambiphiles.The present work is dedicated to the study of metal/Lewis cooperativity. Over years gold has proven its reluctance to undergo elementary steps classicaly disclosed in the coordination chemistry of transition metals. The initial concept behind this research project consist in the installation of a Lewis acid in the first coordination sphere through the coordination of ambiphilic ligands. The ultimate objective is to take full advantage of the assistance provided by the acceptor to extol the reactivity at gold and achieve challenging transformations. The introductive chapter delivers a bibliographic overview of the organometallic chemistry encountered with gold. A peculiar interest is paid to the limitations araising from an intrinsic difficulty to access high oxidation state. The coordination chemistry of ambiphilic ligands is subsequently introduced. The relation between the coordination mode of the ligand and the reactivity of the ensuing complexe is highlighted. To support this research a new mono-ortho-phenylene-phosphinoborane bearing an extremely Lewis acidic boron has been developed. The second chapter brings forward the synthesis of neutral species by coordination of the ambiphilic ligand on gold(I) aryl, methyl and trifluoromethyl complexes. The presence in those species of a gold to boron dative interaction (Z interaction) allowed to assess and discuss the sigma-acceptor ability of the new ligand. Then their reactivity towards oxidative addition has been studied. The third chapter results from a serendipitous discovery made over attemts to generalize the former reactivity. The phosphine borane was found to react with gold(I) alkynyl and alkenyl complexes. via a stereo and regioselective 1,1-phosphaboration process. Zwitterionic complexes stemming from a migration of the organic fragment from the gold to the boron have been authenticated as key intermĂ©diates. Kinetic and DFT investigations suggest a stepwise pathway including the decoordination of the phosphine followed by the anti nucleophilic attack to the unsaturated bond henceforth activated by gold. The boron center acts as a relay and tether for the organic moiety. The last chapter is devoted to the Au(III)/Au(I) reductive elimination. The complexation of a mono-ortho-phenylene-phosphinoborane has shown to foster the challenging C(sp3)-C(sp3) reductive coupling. Kinetic studies emphasised a strong impact of the ligand's Lewis acidity supporting the participation of the acceptor in the mechanism. DFT calculations were performed to elucidate the mechanism and shed light onto a gold/Lewis acid cooperativity

    Ligands ambiphiles et coopérativité métal - acide de Lewis

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    The present work is dedicated to the study of metal/Lewis cooperativity. Over years gold has proven its reluctance to undergo elementary steps classicaly disclosed in the coordination chemistry of transition metals. The initial concept behind this research project consist in the installation of a Lewis acid in the first coordination sphere through the coordination of ambiphilic ligands. The ultimate objective is to take full advantage of the assistance provided by the acceptor to extol the reactivity at gold and achieve challenging transformations. The introductive chapter delivers a bibliographic overview of the organometallic chemistry encountered with gold. A peculiar interest is paid to the limitations araising from an intrinsic difficulty to access high oxidation state. The coordination chemistry of ambiphilic ligands is subsequently introduced. The relation between the coordination mode of the ligand and the reactivity of the ensuing complexe is highlighted. To support this research a new mono-ortho-phenylene-phosphinoborane bearing an extremely Lewis acidic boron has been developed. The second chapter brings forward the synthesis of neutral species by coordination of the ambiphilic ligand on gold(I) aryl, methyl and trifluoromethyl complexes. The presence in those species of a gold to boron dative interaction (Z interaction) allowed to assess and discuss the sigma-acceptor ability of the new ligand. Then their reactivity towards oxidative addition has been studied. The third chapter results from a serendipitous discovery made over attemts to generalize the former reactivity. The phosphine borane was found to react with gold(I) alkynyl and alkenyl complexes. via a stereo and regioselective 1,1-phosphaboration process. Zwitterionic complexes stemming from a migration of the organic fragment from the gold to the boron have been authenticated as key intermĂ©diates. Kinetic and DFT investigations suggest a stepwise pathway including the decoordination of the phosphine followed by the anti nucleophilic attack to the unsaturated bond henceforth activated by gold. The boron center acts as a relay and tether for the organic moiety. The last chapter is devoted to the Au(III)/Au(I) reductive elimination. The complexation of a mono-ortho-phenylene-phosphinoborane has shown to foster the challenging C(sp3)-C(sp3) reductive coupling. Kinetic studies emphasised a strong impact of the ligand's Lewis acidity supporting the participation of the acceptor in the mechanism. DFT calculations were performed to elucidate the mechanism and shed light onto a gold/Lewis acid cooperativity.Cette thĂšse porte sur l'Ă©tude de la coopĂ©rativitĂ© mĂ©tal/acide de Lewis. L'or se distingue des autres mĂ©taux de transitions par une rĂ©ticence Ă  s'engager dans les Ă©tapes Ă©lĂ©mentaires classiquement rencontrĂ©es en chimie organomĂ©tallique. Ce projet de recherche repose sur la coordination de l'or par des ligands ambiphiles permettant l'installation d'un acide de Lewis dans la sphĂšre de coordination. L'objectif ici est de tirer profit de la proximitĂ© de l'accepteur pour exalter la rĂ©activitĂ© de l'or et rĂ©aliser des transformations initialement dĂ©favorables. Le premier chapitre aborde de maniĂšre trĂšs gĂ©nĂ©rale l'Ă©tat de l'art de la chimie organomĂ©tallique de l'or. Une attention particuliĂšre est portĂ©e aux limitations gĂ©nĂ©rĂ©es par une difficultĂ© intrinsĂšque de ce mĂ©tal Ă  accĂ©der Ă  de hauts degrĂ©s d'oxydations. La coordination des ligands ambiphiles sur l'or y est introduite dans un second temps. La relation entre les divers modes de coordinations adoptĂ©s et la rĂ©activitĂ© des complexes rĂ©sultant a Ă©tĂ© mise en avant. Le deuxiĂšme chapitre est consacrĂ© Ă  la synthĂšse de nouveaux complexes d'or PB-Au(I)-R comportant un co-ligand organique. Ces derniers ont Ă©tĂ© obtenu depuis des prĂ©curseurs aryle, mĂ©thyle et trifluoromĂ©thyle d'Au(I) par coordination d'une phosphine borane rĂ©cemment dĂ©crite par l'Ă©quipe et prĂ©sentant un fragment borane hautement acide de Lewis. La prĂ©sence d'une interaction datives de l'or vers le bore a pu ĂȘtre Ă©tabli. L'Ă©valuation de la force de l'interaction Au→B a notamment permis de discuter le caractĂšre sigma-accepteur du nouveau ligand. L'addition oxydante de divers Ă©lectrophiles a ensuite Ă©tĂ© Ă©tudiĂ©e. Lors l'exploration de la rĂ©activitĂ© des complexes PB-Au(I)-R (R = vinyle, acĂ©tylĂšnyle), une rĂ©action de 1,1-phosphaboration stĂ©rĂ©o- et rĂ©giosĂ©lective du groupement insaturĂ© a Ă©tĂ© dĂ©couverte et fera l'objet d'un troisiĂšme chapitre. Des complexes zwittĂ©rioniques issus de l'abstraction du groupement organique de l'or vers le bore ont Ă©tĂ© identifiĂ©s comme intermĂ©diaire clĂ© de la transformation. Le mĂ©canisme de la rĂ©action a fait l'objet d'une Ă©tude expĂ©rimentale et thĂ©orique mettant en Ă©vidence une action concertĂ©e du bore et de l'or. Enfin, il a Ă©tĂ© dĂ©montrĂ© dans un dernier chapitre que la coordination des mono-phosphines boranes sur les complexes d'Au(III) favorise grandement l'Ă©limination rĂ©ductrice C(sp3)-C(sp3) connue pour ĂȘtre difficile. Des Ă©tudes cinĂ©tiques montrent un impact de la prĂ©sence de l'acide de Lewis. L'Ă©tude par DFT du mĂ©canisme soutient la participation du borane des ligands ambiphiles

    Zirconium(IV)-catalysed hydrosilylation of organic carbonates and polycarbonates household wastes into alcohol derivatives.

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    The Schwartz’s reagent Cp2Zr(H)Cl is a well known stoichiometric reagent for the reduction of unsaturated organic molecules but it has rarely been used in catalytic transformations. Herein, we describe the reduction of a variety of organic carbonates using the catalyst Cp2Zr(H)Cl in combination with Me(MeO)2SiH (DMMS) as reductant. This method was further applied to the reductive depolymerization of some polycarbonate materials and yielded sylilated alcohols and diols in mild conditions. A significant advantage of this recycling method of polycarbonates is its stability towards the additives contained in household plastics and its ability to selectively depolymerize polycarbonate in a mixture containing a polyester and a polycarbonate. Experimental investigations brought evidences on a mechanism based on the hydrozirconation of the carbonyl fragment, thermal σ C–O bond cleavage, and Zr–OR/Si–H σ-bond metathesis reactions to regenerate the hydride catalyst

    Mechanistic Investigations on Hydrogenation, Isomerization and Hydrosilylation Reactions Mediated by a Germyl-Rhodium System

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    We recently disclosed a dehydrogenative double C−H bond activation reaction in the unusual pincer-type rhodium-germyl complex [(ArMes)2ClGeRh] (ArMes=C6H3-2,6-(C6H2-2,4,6-Me3)2). Herein we investigate the catalytic applications of this Rh/Ge system in several transformations, namely trans-semihydrogenation of internal alkynes, trans-isomerization of olefins and hydrosilylation of alkynes. We have compared the activity and selectivity of this catalyst against other common rhodium precursors, as well as related sterically hindered rhodium complexes, being the one with the germyl fragment superior in terms of selectivity towards E-isomers. To increase this selectivity, a tandem catalytic protocol that incorporates the use of a heterogeneous catalyst for the trans-semihydrogenation of internal alkynes has been devised. Kinetic mechanistic investigations provide important information regarding the individual catalytic cycles that comprise the overall trans-semihydrogenation of internal alkynes.This work has been supported by the European Research Council (ERC Starting Grant, CoopCat, 756575) and Junta de Andalucia (P18-FR-4688). SB acknowledges Marie SkƂodowska-Curie program for a postdoctoral fellowship (project 101023461).Peer reviewe

    Tuning the Inorganic Core of a reduced Ni2Ge2 Cluster

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    Tetranuclear cores (M−E)2 of transition metals (M) and tetrylenes (EII=Si, Ge, Sn) are key motifs in homogeneous and heterogeneous catalysis. They exhibit a continuum of M−M and E−E bonding within the inorganic core that leads to a variety of structures for which there are no specific synthetic methods. Herein, we report a series of highly reduced [Ni0GeII]2 squares solely stabilized by bulky terphenyl (C6H3−2,6-Ar2) ligands, for which we provide complementary and high-yielding syntheses. Reactivity studies with common Lewis bases (carbene and CO) evince that the structure of the (M−E)2 core can be transformed. We have investigated this core modification by computational means, offering a rationale to better understand the continuum of bonding across these clusters.European Research Council (ERC Starting Grant, CoopCat, 756575)MCIN/AEI/ 10.13039/501100011033(PID2019-110856GA-I00)PID2022139782 NB-I00/AEI/10.13039/501100011033/FEDER, U

    Lewis Acid-Assisted C(sp 3 )–C(sp 3 ) Reductive Elimination at Gold

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    International audienceThe phosphine-borane iPr2P(o-C6H4)BFxyl2 (Fxyl = 3,5-(F3C)2C6H3) 1-Fxyl was found to promote the reductive elimination of ethane from [AuMe2(ÎŒ-Cl)]2. Nuclear magnetic resonance monitoring revealed the intermediate formation of the (1-Fxyl)AuMe2Cl complex. Density functional theory calculations identified a zwitterionic path as the lowest energy profile, with an overall activation barrier more than 10 kcal/mol lower than without borane assistance. The Lewis acid moiety first abstracts the chloride to generate a zwitterionic Au(III) complex, which then readily undergoes C(sp3)–C(sp3) coupling. The chloride is finally transferred back from boron to gold. The electronic features of this Lewis-assisted reductive elimination at gold have been deciphered by intrinsic bond orbital analyses. Sufficient Lewis acidity of boron is required for the ambiphilic ligand to trigger the C(sp3)–C(sp3) coupling, as shown by complementary studies with two other phosphine-boranes, and the addition of chlorides slows down the reductive elimination of ethane

    Gold-to-Boron Aryl Transfer from a T-Shaped Phosphine–Borane Gold(I) Complex

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    International audienceT-shaped gold(I) complexes with significant Au→B interactions were prepared from the phosphine–borane i-Pr2P(o-C6H4)BFXyl2 [Fxyl = 3,5-(F3C)2C6H3]. The (P,B)AuArF complex 4 [ArF = 4-(F3C)C6H4] was obtained by an indirect route involving ligand exchange from (ArO)3PAuArF3a [Ar = 2,4-(t-Bu)2C6H3]. A different outcome was observed with the analogous precursor (MeO)3PAuArF3b. Here, the phosphite remains bonded to gold, and the borane moiety abstracts the ArF group from gold to give the zwitterionic dicoordinate gold(I) complex 5. DFT calculations support a 2-step associative pathway for this gold-to-boron aryl transfer. It involves a square-planar gold(I) complex with enhanced Au→B interaction as key intermediate and proceeds via a 3-center transition state

    1,1-Phosphaboration of C≡C and C=C bonds at gold

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    International audienceThe phosphine-borane iPr2P(o-C6H4)BFXyl2 (Fxyl = 3,5-(F3C)2C6H3) was found to react with gold(i) alkynyl and vinyl complexes via an original 1,1-phosphaboration process. Zwitterionic complexes resulting from Au to B transmetallation have been authenticated as key intermediates. X-ray diffraction analyses show that the alkynyl-borate moiety remains pendant while the vinyl-borate is side-on coordinated to gold. According to DFT calculations, the phosphaboration then proceeds in a trans stepwise manner via decoordination of the phosphine, followed by anti nucleophilic attack to the π-CC bond activated by gold. The boron center acts as a relay and tether for the organic group

    A catalytic fluoride-rebound mechanism for C(sp3)-CF3 bond formation.

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    The biological properties of trifluoromethyl compounds have led to their ubiquity in pharmaceuticals, yet their chemical properties have made their preparation a substantial challenge, necessitating innovative chemical solutions. We report the serendipitous discovery of a borane-catalyzed formal C(sp3)-CF3 reductive elimination from Au(III) that accesses these compounds by a distinct mechanism proceeding via fluoride abstraction, migratory insertion, and C-F reductive elimination to achieve a net C-C bond construction. The parent bis(trifluoromethyl)Au(III) complexes tolerate a surprising breadth of synthetic protocols, enabling the synthesis of complex organic derivatives without cleavage of the Au-C bond. This feature, combined with the "fluoride-rebound" mechanism, was translated into a protocol for the synthesis of 18F-radiolabeled aliphatic CF3-containing compounds, enabling the preparation of potential tracers for use in positron emission tomography
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