11 research outputs found
Ligands bidentes en chimie de l'or : de la stabilisation d'espÚces réactives à la catalyse
Cette thĂšse porte sur l'Ă©tude de complexes dĂ©finis d'or, de la stabilisation de composĂ©s originaux Ă leur utilisation pour de nouvelles transformations. Une approche conjointe expĂ©rience/thĂ©orie a Ă©tĂ© employĂ©e. De nouveaux complexes d'or ont Ă©tĂ© synthĂ©tisĂ©s et caractĂ©risĂ©s par diffĂ©rentes techniques spectroscopiques et de diffractomĂ©trie. Leurs rĂ©activitĂ©s, notamment dans des procĂ©dĂ©s catalytiques, ont Ă©tĂ© Ă©tudiĂ©es. Les calculs DFT ont aiguillĂ© le choix des ligands/complexes d'intĂ©rĂȘts. Ils ont permis d'analyser la structure Ă©lectronique des nouvelles espĂšces isolĂ©es et d'Ă©lucider les mĂ©canismes mis en jeu. Une vue d'ensemble de l'utilisation de ligands bidentes pour la chimie de l'or montrant leurs implications dans le dĂ©veloppement de cette chimie est prĂ©sentĂ© dans le premier chapitre. Une comparaison des diffĂ©rents ligands bidentes accessibles rationnalise le choix de deux d'entre eux pour les Ă©tudes prĂ©sentĂ©es par la suite. Le second chapitre concerne le dĂ©veloppement de la rĂ©action d'hĂ©tĂ©roarylation des alcĂšnes catalysĂ©e par le complexe MeDalPhosAuCl. Cette nouvelle transformation procĂšde via un cycle catalytique Au^I/Au^III et combine addition oxydante et activation PI Ă l'or. Un mĂ©canisme dĂ©taillĂ© est proposĂ© sur la base d'analyses RMN in situ, d'Ă©tude par marquage au deutĂ©rium et de calculs DFT. La rĂ©action a pu ĂȘtre gĂ©nĂ©ralisĂ©e Ă un large panel de substrats et un changement inhabituel de rĂ©giosĂ©lectivitĂ© a Ă©tĂ© observĂ© pour les alcĂšnes internes cis ou trans. Le troisiĂšme chapitre est dĂ©diĂ© Ă l'isolation et la caractĂ©risation des premiers complexes d'or impliquant des liaisons hydrogĂšnes Au···H-X. GrĂące aux ligands hĂ©milabiles (P,N), un contact proche entre l'or et l'hydrogĂšne a Ă©tĂ© observĂ© par DRX et la prĂ©sence de la liaison hydrogĂšne N-H···Au a Ă©tĂ© dĂ©montrĂ©e sans ambiguĂŻtĂ© par spectroscopies RMN et IR. La nature de cette liaison a Ă©tĂ© mĂ©ticuleusement analysĂ©e par calcul DFT fournissant des arguments en faveur d'une liaison hydrogĂšne, interaction attractive non-covalente. Une Ă©tude in silico sur de nouveaux modĂšles, avec des interactions Au···H-X potentielles (X = N, O ou P, variations des ligands ou de l'encombrement stĂ©rique) a Ă©tĂ© rĂ©alisĂ©e pour donner des directives aux futurs travaux expĂ©rimentaux. Le quatriĂšme chapitre porte sur l'Ă©tude de carbĂšnes alpha-CF_3 d'or(I). L'intĂ©rĂȘt est double : 1) trĂšs peu de carbĂšnes alpha-CF_3 ont Ă©tĂ© isolĂ©s et caractĂ©risĂ©s et 2) beaucoup de molĂ©cules bioactives ou de matĂ©riaux possĂšdent des substituants CF_3 augmentant l'intĂ©rĂȘt pour les rĂ©actions de trifluoromĂ©thylation. GrĂące au ligand bis-phosphine o-carborane, plusieurs carbĂšnes alpha-CF_3 d'or(I) ont Ă©tĂ© synthĂ©tisĂ©s, isolĂ©s et complĂštement caractĂ©risĂ©s par spectroscopie RMN multi nuclĂ©aire, DRX et spectromĂ©trie de masse. La liaison M=C_carbĂšne a Ă©tĂ© analysĂ©e par calculs DFT avec une attention particuliĂšre pour la description des orbitales molĂ©culaires et la contribution relative donation/rĂ©trodonation entre le fragment mĂ©tallique et le carbĂšne. La rĂ©activitĂ© de ces nouveaux carbĂšnes d'or vis-Ă -vis de rĂ©actions d'insertion et de cyclopropanation a Ă©tĂ© Ă©tudiĂ©e montrant que ces espĂšces imitent les carbĂšnes alpha-CF_3 transitoires postulĂ©s pour d'autres mĂ©taux de transition.The present work deals with the study of defined gold complexes from the stabilization of original compounds to their use for novel transformations. A joint experimental/theoretical approach has been used. New gold complexes were synthesized and characterized by different spectroscopic means and diffractometry. Their reactivities notably in catalytic process were studied. DFT calculations guided for the choice of ligands/complexes of interest. They helped to analyze the electronic bonding of the new isolated species and to elucidate the involved mechanism. An overview of the use of bidentate ligand in gold chemistry showing their involvement in the expansion of this field is presented in the first chapter. A comparison of the different bidentate ligands available rationalize the choice of two of them for the following studies. The second chapter concerns the development of hetero-arylation reaction of alkenes catalyzed by the MeDalPhosAuCl complex. This new transformation proceeds via Au^I/Au^III catalytic cycle and merge oxidative addition and PI-activation at gold. A detail mechanism is suggested based on in situ NMR analyses, deuterium labelling studies and DFT calculations. The scope of the reaction has been explored for a large number of substrates and an unusual switch of regioselectivity was observed for internal alkenes cis or trans. The third chapter is dedicated to the isolation and characterization of the first gold complexes involving Au···H-X hydrogen bonding. Taking advantage of the hemilabile (P,N) ligands, a close contact between gold and hydrogen was observed by XRD and the presence of N-H···Au hydrogen bond was unambiguously demonstrated by NMR and IR spectroscopies. The nature of this bonding was thoroughly analyzed by DFT providing compelling evidence for noncovalent attractive hydrogen-type bonding. An in silico study on new models, with potential Au···H-X interaction (X = N, O or P, ligand and steric hindrance modulation) have been performed to provide guidelines for further synthetic work. The fourth chapter focused on the study of alpha-CF_3 gold(I) carbene complexes. The interest is twofold: 1) very few alpha-CF_3 carbene complexes have been isolated and characterized and 2) many bioactive molecules or materials bear CF_3 substituents, increasing the interest for trifluoromethylation reactions. Taking advantage of the o-carborane diphosphine ligand, several alpha-CF_3 gold carbene complexes were synthesized, isolated and fully characterized, at low temperature, by means of multinuclear NMR spectroscopy, XRD and mass spectrometry. The M=C_carbene bonding situation was analyzed carefully by DFT calculations with particular attention to the description of molecular orbitals and to the relative donation/retrodonation contribution between the metallic fragment and the carbene. The reactivity of this new gold carbene towards insertion reaction and cyclopropanation was studied showing that they mimic transient alpha-CF_3 metal carbene complexes
Bidimensional lamellar assembly by coordination of peptidic homopolymers to platinum nanoparticles
A key challenge for designing hybrid materials is the development of chemical tools to control the organization of inorganic nanoobjects at low scales, from mesoscopic (~”m) to nanometric (~nm). So far, the most efficient strategy to align assemblies of nanoparticles consists in a bottom-up approach by decorating block copolymer lamellae with nanoobjects. This well accomplished procedure is nonetheless limited by the thermodynamic constraints that govern copolymer assembly, the entropy of mixing as described by the FloryâHuggins solution theory supplemented by the critical influence of the volume fraction of the block components. Here we show that a completely different approach can lead to tunable 2D lamellar organization of nanoparticles with homopolymers only, on condition that few elementary rules are respected: 1) the polymer spontaneously allows a structural preorganization, 2) the polymer owns functional groups that interact with the nanoparticle surface, 3) the nanoparticles show a surface accessible for coordination
Spin crossover in Fe(triazole)âPt nanoparticle self-assembly structured at the sub-5 nm scale
A main goal of molecular electronics is to relate the performance of devices to the structure and electronic state of molecules. Among the variety of possibilities that organic, organometallic and coordination chemistries offer to tune the energy levels of molecular components, spin crossover phenomenon is a perfect candidate for elaboration of molecular switches. The reorganization of the electronic state population of the molecules associated to the spin crossover can indeed lead to a significant change in conductivity. However, molecular spin crossover is very sensitive to the environment and can disappear once the molecules are integrated into devices. Here, we show that the association of ultra-small 1.2 nm platinum nanoparticles with FeII triazole-based spin crossover coordination polymers leads to self-assemblies, extremely well organized at the sub-3 nm scale. The quasi-perfect alignment of nanoparticles observed by transmission electron microscopy, in addition to specific signature in infrared spectroscopy, demonstrates the coordination of the long-chain molecules with the nanoparticles. Spin crossover is confirmed in such assemblies by X-ray absorption spectroscopic measurements and shows unambiguous characteristics both in magnetic and charge transport measurements. Coordinating polymers are therefore ideal candidates for the elaboration of robust, well-organized, hybrid self-assemblies with metallic nanoparticles, while maintaining sensitive functional properties, such as spin crossover
Bidentate ligands in gold chemistry : from stabilization of reactive species to catalysis
Cette thĂšse porte sur l'Ă©tude de complexes dĂ©finis d'or, de la stabilisation de composĂ©s originaux Ă leur utilisation pour de nouvelles transformations. Une approche conjointe expĂ©rience/thĂ©orie a Ă©tĂ© employĂ©e. De nouveaux complexes d'or ont Ă©tĂ© synthĂ©tisĂ©s et caractĂ©risĂ©s par diffĂ©rentes techniques spectroscopiques et de diffractomĂ©trie. Leurs rĂ©activitĂ©s, notamment dans des procĂ©dĂ©s catalytiques, ont Ă©tĂ© Ă©tudiĂ©es. Les calculs DFT ont aiguillĂ© le choix des ligands/complexes d'intĂ©rĂȘts. Ils ont permis d'analyser la structure Ă©lectronique des nouvelles espĂšces isolĂ©es et d'Ă©lucider les mĂ©canismes mis en jeu. Une vue d'ensemble de l'utilisation de ligands bidentes pour la chimie de l'or montrant leurs implications dans le dĂ©veloppement de cette chimie est prĂ©sentĂ© dans le premier chapitre. Une comparaison des diffĂ©rents ligands bidentes accessibles rationnalise le choix de deux d'entre eux pour les Ă©tudes prĂ©sentĂ©es par la suite. Le second chapitre concerne le dĂ©veloppement de la rĂ©action d'hĂ©tĂ©roarylation des alcĂšnes catalysĂ©e par le complexe MeDalPhosAuCl. Cette nouvelle transformation procĂšde via un cycle catalytique Au^I/Au^III et combine addition oxydante et activation PI Ă l'or. Un mĂ©canisme dĂ©taillĂ© est proposĂ© sur la base d'analyses RMN in situ, d'Ă©tude par marquage au deutĂ©rium et de calculs DFT. La rĂ©action a pu ĂȘtre gĂ©nĂ©ralisĂ©e Ă un large panel de substrats et un changement inhabituel de rĂ©giosĂ©lectivitĂ© a Ă©tĂ© observĂ© pour les alcĂšnes internes cis ou trans. Le troisiĂšme chapitre est dĂ©diĂ© Ă l'isolation et la caractĂ©risation des premiers complexes d'or impliquant des liaisons hydrogĂšnes Au···H-X. GrĂące aux ligands hĂ©milabiles (P,N), un contact proche entre l'or et l'hydrogĂšne a Ă©tĂ© observĂ© par DRX et la prĂ©sence de la liaison hydrogĂšne N-H···Au a Ă©tĂ© dĂ©montrĂ©e sans ambiguĂŻtĂ© par spectroscopies RMN et IR. La nature de cette liaison a Ă©tĂ© mĂ©ticuleusement analysĂ©e par calcul DFT fournissant des arguments en faveur d'une liaison hydrogĂšne, interaction attractive non-covalente. Une Ă©tude in silico sur de nouveaux modĂšles, avec des interactions Au···H-X potentielles (X = N, O ou P, variations des ligands ou de l'encombrement stĂ©rique) a Ă©tĂ© rĂ©alisĂ©e pour donner des directives aux futurs travaux expĂ©rimentaux. Le quatriĂšme chapitre porte sur l'Ă©tude de carbĂšnes alpha-CF_3 d'or(I). L'intĂ©rĂȘt est double : 1) trĂšs peu de carbĂšnes alpha-CF_3 ont Ă©tĂ© isolĂ©s et caractĂ©risĂ©s et 2) beaucoup de molĂ©cules bioactives ou de matĂ©riaux possĂšdent des substituants CF_3 augmentant l'intĂ©rĂȘt pour les rĂ©actions de trifluoromĂ©thylation. GrĂące au ligand bis-phosphine o-carborane, plusieurs carbĂšnes alpha-CF_3 d'or(I) ont Ă©tĂ© synthĂ©tisĂ©s, isolĂ©s et complĂštement caractĂ©risĂ©s par spectroscopie RMN multi nuclĂ©aire, DRX et spectromĂ©trie de masse. La liaison M=C_carbĂšne a Ă©tĂ© analysĂ©e par calculs DFT avec une attention particuliĂšre pour la description des orbitales molĂ©culaires et la contribution relative donation/rĂ©trodonation entre le fragment mĂ©tallique et le carbĂšne. La rĂ©activitĂ© de ces nouveaux carbĂšnes d'or vis-Ă -vis de rĂ©actions d'insertion et de cyclopropanation a Ă©tĂ© Ă©tudiĂ©e montrant que ces espĂšces imitent les carbĂšnes alpha-CF_3 transitoires postulĂ©s pour d'autres mĂ©taux de transition.The present work deals with the study of defined gold complexes from the stabilization of original compounds to their use for novel transformations. A joint experimental/theoretical approach has been used. New gold complexes were synthesized and characterized by different spectroscopic means and diffractometry. Their reactivities notably in catalytic process were studied. DFT calculations guided for the choice of ligands/complexes of interest. They helped to analyze the electronic bonding of the new isolated species and to elucidate the involved mechanism. An overview of the use of bidentate ligand in gold chemistry showing their involvement in the expansion of this field is presented in the first chapter. A comparison of the different bidentate ligands available rationalize the choice of two of them for the following studies. The second chapter concerns the development of hetero-arylation reaction of alkenes catalyzed by the MeDalPhosAuCl complex. This new transformation proceeds via Au^I/Au^III catalytic cycle and merge oxidative addition and PI-activation at gold. A detail mechanism is suggested based on in situ NMR analyses, deuterium labelling studies and DFT calculations. The scope of the reaction has been explored for a large number of substrates and an unusual switch of regioselectivity was observed for internal alkenes cis or trans. The third chapter is dedicated to the isolation and characterization of the first gold complexes involving Au···H-X hydrogen bonding. Taking advantage of the hemilabile (P,N) ligands, a close contact between gold and hydrogen was observed by XRD and the presence of N-H···Au hydrogen bond was unambiguously demonstrated by NMR and IR spectroscopies. The nature of this bonding was thoroughly analyzed by DFT providing compelling evidence for noncovalent attractive hydrogen-type bonding. An in silico study on new models, with potential Au···H-X interaction (X = N, O or P, ligand and steric hindrance modulation) have been performed to provide guidelines for further synthetic work. The fourth chapter focused on the study of alpha-CF_3 gold(I) carbene complexes. The interest is twofold: 1) very few alpha-CF_3 carbene complexes have been isolated and characterized and 2) many bioactive molecules or materials bear CF_3 substituents, increasing the interest for trifluoromethylation reactions. Taking advantage of the o-carborane diphosphine ligand, several alpha-CF_3 gold carbene complexes were synthesized, isolated and fully characterized, at low temperature, by means of multinuclear NMR spectroscopy, XRD and mass spectrometry. The M=C_carbene bonding situation was analyzed carefully by DFT calculations with particular attention to the description of molecular orbitals and to the relative donation/retrodonation contribution between the metallic fragment and the carbene. The reactivity of this new gold carbene towards insertion reaction and cyclopropanation was studied showing that they mimic transient alpha-CF_3 metal carbene complexes
Mechanistic Insights about the LigandâEnabled Oxyâarylation/vinylation of Alkenes via Au(I)/Au(III) Catalysis
International audienceThe mechanism of oxy-arylation/vinylation of alkenes catalyzed by the (MeDalphos)AuCl complex was comprehensively investigated by DFT. (P,N)Au(Ph) 2 + and (P,N)Au(vinyl) 2 + are key intermediates accounting for the activation of the alkenols and for their cyclization by outersphere nucleophilic attack of oxygen. The 5-exo and 6-endo paths have been computed and compared, reproducing the peculiar regioselectivity difference observed experimentally between 4-penten-1-ol, (E) and (Z)-4-hexen-1-ols. Examining the way the alkenol coordinates to gold (more η 2 or η 1) can offer, in some cases, a simple way to predict the favored path of cyclization
Gold(I) 뱉Trifluoromethyl Carbenes: Synthesis, Characterization and Reactivity Studies
International audienceAryl trifluoromethyl diazomethanes 2-R (R = Ph, OMe, CF 3) are readily decomposed by the (o-carboranyl)diphosphine gold(I) complex 1. The resulting α-CF 3 substituted carbene complexes 3-R have been characterized by multi-nuclear NMR spectroscopy as well as X-ray crystallography (for 3-Ph). The bonding situation was thoroughly assessed by computational means, showing stabilization of the electrophilic carbene center by Ï-donation from the aryl substituent and backdonation from Au, as enhanced by the chelating P^P ligand. Reactivity studies under stoichiometric and catalytic conditions substantiate typical carbene-type behavior for 3-Ph
Gold(I)/Gold(III) Catalysis that Merges Oxidative Addition and ÏâAlkene Activation
International audienceThe hetero-arylation of alkenes with aryl iodides has been efficiently achieved with the (MeDalphos)AuCl complex via Au(I)/Au(III) catalysis. The possibility to combine oxidative addition of aryl iodides and Ï-activation of alkenes at gold is demonstrated for the first time. The reaction is robust and general (>30 examples including internal alkenes, 5, 6 and 7-membered rings). It is regioselective and leads exclusively to trans addition products. The (P,N) gold complex is most efficient with electron-rich aryl substrates, which are troublesome with alternative photoredox / oxidative approaches. In addition, it actuates a very unusual switch in regioselectivity from 5-exo to 6-endo cyclization between the Z and E isomers of internal alkenols
CâC CrossâCouplings from a Cyclometalated Au(III) CN Complex: Mechanistic Insights and Synthetic Developments
International audienceIn recent years, the reactivity of gold complexes was shown to extend well beyond Ï-activation and to hold promises to achieve selective cross-couplings in several CâC and CâE (E=heteroatom) bond forming reactions. Here, with the aim of exploiting new organometallic species for cross-coupling reactions, we report on the Au(III)-mediated C(sp2)âC(sp) occurring upon reaction of the cyclometalated complex [Au(CCH2N)Cl2] (1, CCH2N=2-benzylpyridine) with AgPhCC. The reaction progress has been monitored by NMR spectroscopy, demonstrating the involvement of a number of key intermediates, whose structures have been unambiguously ascertained through 1D and 2D NMR analyses (1H, 13C, 1H-1H COSY, 1H-13C HSQC and 1H-13C HMBC) as well as by HR-ESI-MS and X-ray diffraction studies. Furthermore, crystallographic studies have serendipitously resulted in the authentication of zwitterionic Au(I) complexes as side-products arising from cyclization of the coupling product in the coordination sphere of gold. The experimental work has been paralleled and complemented by DFT calculations of the reaction profiles, providing valuable insight into the structure and energetics of the key intermediates and transition states, as well as on the coordination sphere of gold along the whole process. Of note, the broader scope of the cross-coupling at the Au(III) CCH2N centre has also been demonstrated studying the reaction of 1 with C(sp2)-based nucleophiles, namely vinyl and heteroaryl tin and zinc reagents. These reactions stand as rare examples of C(sp2)âC(sp2) cross-couplings at Au(III)
Evidence for Genuine Hydrogen Bonding in Gold(I) Complexes
International audienceThe ability of gold to act as proton acceptor and participate in hydrogen bonding remains an open question. Here we report the synthesis and characterization of cationic gold(I) complexes featuring ditopic phosphine-ammonium (P,NH +) ligands. Besides the presence of short AuâąâąâąH contacts in the solid state, the presence of AuâąâąâąH-N hydrogen bonds has been inferred by NMR and IR spectroscopies. The bonding situation has been extensively analysed computationally. All features are consistent with the presence of 3-center 4-electron attractive interactions combining electrostatic and orbital components. The role of relativistic effects has been examined and the analysis has been extended to other recently described gold(I) complexes
Redox Catalysis Facilitates Lignin Depolymerization
Lignin is a recalcitrant
and underexploited natural feedstock for
aromatic commodity chemicals, and its degradation generally requires
the use of high temperatures and harsh reaction conditions. Herein
we present an ambient temperature one-pot process for the controlled
oxidation and depolymerization of this potent resource. Harnessing
the potential of electrocatalytic oxidation in conjugation with our
photocatalytic cleavage methodology, we have developed an operationally
simple procedure for selective fragmentation of ÎČ-O-4 bonds
with excellent mass recovery, which provides a unique opportunity
to expand the existing lignin usage from energy source to commodity
chemicals and synthetic building block source