Ligands bidentes en chimie de l'or : de la stabilisation d'espèces réactives à la catalyse

Cette thèse porte sur l'étude de complexes définis d'or, de la stabilisation de composés originaux à leur utilisation pour de nouvelles transformations. Une approche conjointe expérience/théorie a été employée. De nouveaux complexes d'or ont été synthétisés et caractérisés par différentes techniques spectroscopiques et de diffractométrie. Leurs réactivités, notamment dans des procédés catalytiques, ont été étudiées. Les calculs DFT ont aiguillé le choix des ligands/complexes d'intérêts. Ils ont permis d'analyser la structure électronique des nouvelles espèces isolées et d'élucider les mécanismes mis en jeu. Une vue d'ensemble de l'utilisation de ligands bidentes pour la chimie de l'or montrant leurs implications dans le développement de cette chimie est présenté dans le premier chapitre. Une comparaison des différents ligands bidentes accessibles rationnalise le choix de deux d'entre eux pour les études présentées par la suite. Le second chapitre concerne le développement de la réaction d'hétéroarylation des alcènes catalysée par le complexe MeDalPhosAuCl. Cette nouvelle transformation procède via un cycle catalytique Au^I/Au^III et combine addition oxydante et activation PI à l'or. Un mécanisme détaillé est proposé sur la base d'analyses RMN in situ, d'étude par marquage au deutérium et de calculs DFT. La réaction a pu être généralisée à un large panel de substrats et un changement inhabituel de régiosélectivité a été observé pour les alcènes internes cis ou trans. Le troisième chapitre est dédié à l'isolation et la caractérisation des premiers complexes d'or impliquant des liaisons hydrogènes Au···H-X. Grâce aux ligands hémilabiles (P,N), un contact proche entre l'or et l'hydrogène a été observé par DRX et la présence de la liaison hydrogène N-H···Au a été démontrée sans ambiguïté par spectroscopies RMN et IR. La nature de cette liaison a été méticuleusement analysée par calcul DFT fournissant des arguments en faveur d'une liaison hydrogène, interaction attractive non-covalente. Une étude in silico sur de nouveaux modèles, avec des interactions Au···H-X potentielles (X = N, O ou P, variations des ligands ou de l'encombrement stérique) a été réalisée pour donner des directives aux futurs travaux expérimentaux. Le quatrième chapitre porte sur l'étude de carbènes alpha-CF_3 d'or(I). L'intérêt est double : 1) très peu de carbènes alpha-CF_3 ont été isolés et caractérisés et 2) beaucoup de molécules bioactives ou de matériaux possèdent des substituants CF_3 augmentant l'intérêt pour les réactions de trifluorométhylation. Grâce au ligand bis-phosphine o-carborane, plusieurs carbènes alpha-CF_3 d'or(I) ont été synthétisés, isolés et complètement caractérisés par spectroscopie RMN multi nucléaire, DRX et spectrométrie de masse. La liaison M=C_carbène a été analysée par calculs DFT avec une attention particulière pour la description des orbitales moléculaires et la contribution relative donation/rétrodonation entre le fragment métallique et le carbène. La réactivité de ces nouveaux carbènes d'or vis-à-vis de réactions d'insertion et de cyclopropanation a été étudiée montrant que ces espèces imitent les carbènes alpha-CF_3 transitoires postulés pour d'autres métaux 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 (~µm) 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 Flory–Huggins 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)–Pt 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 thèse porte sur l'étude de complexes définis d'or, de la stabilisation de composés originaux à leur utilisation pour de nouvelles transformations. Une approche conjointe expérience/théorie a été employée. De nouveaux complexes d'or ont été synthétisés et caractérisés par différentes techniques spectroscopiques et de diffractométrie. Leurs réactivités, notamment dans des procédés catalytiques, ont été étudiées. Les calculs DFT ont aiguillé le choix des ligands/complexes d'intérêts. Ils ont permis d'analyser la structure électronique des nouvelles espèces isolées et d'élucider les mécanismes mis en jeu. Une vue d'ensemble de l'utilisation de ligands bidentes pour la chimie de l'or montrant leurs implications dans le développement de cette chimie est présenté dans le premier chapitre. Une comparaison des différents ligands bidentes accessibles rationnalise le choix de deux d'entre eux pour les études présentées par la suite. Le second chapitre concerne le développement de la réaction d'hétéroarylation des alcènes catalysée par le complexe MeDalPhosAuCl. Cette nouvelle transformation procède via un cycle catalytique Au^I/Au^III et combine addition oxydante et activation PI à l'or. Un mécanisme détaillé est proposé sur la base d'analyses RMN in situ, d'étude par marquage au deutérium et de calculs DFT. La réaction a pu être généralisée à un large panel de substrats et un changement inhabituel de régiosélectivité a été observé pour les alcènes internes cis ou trans. Le troisième chapitre est dédié à l'isolation et la caractérisation des premiers complexes d'or impliquant des liaisons hydrogènes Au···H-X. Grâce aux ligands hémilabiles (P,N), un contact proche entre l'or et l'hydrogène a été observé par DRX et la présence de la liaison hydrogène N-H···Au a été démontrée sans ambiguïté par spectroscopies RMN et IR. La nature de cette liaison a été méticuleusement analysée par calcul DFT fournissant des arguments en faveur d'une liaison hydrogène, interaction attractive non-covalente. Une étude in silico sur de nouveaux modèles, avec des interactions Au···H-X potentielles (X = N, O ou P, variations des ligands ou de l'encombrement stérique) a été réalisée pour donner des directives aux futurs travaux expérimentaux. Le quatrième chapitre porte sur l'étude de carbènes alpha-CF_3 d'or(I). L'intérêt est double : 1) très peu de carbènes alpha-CF_3 ont été isolés et caractérisés et 2) beaucoup de molécules bioactives ou de matériaux possèdent des substituants CF_3 augmentant l'intérêt pour les réactions de trifluorométhylation. Grâce au ligand bis-phosphine o-carborane, plusieurs carbènes alpha-CF_3 d'or(I) ont été synthétisés, isolés et complètement caractérisés par spectroscopie RMN multi nucléaire, DRX et spectrométrie de masse. La liaison M=C_carbène a été analysée par calculs DFT avec une attention particulière pour la description des orbitales moléculaires et la contribution relative donation/rétrodonation entre le fragment métallique et le carbène. La réactivité de ces nouveaux carbènes d'or vis-à-vis de réactions d'insertion et de cyclopropanation a été étudiée montrant que ces espèces imitent les carbènes alpha-CF_3 transitoires postulés pour d'autres métaux 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 Ligand‐Enabled Oxy‐arylation/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) α‐Trifluoromethyl 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 π-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 π‐Alkene 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 π-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

C−C Cross‐Couplings 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 π-activation and to hold promises to achieve selective cross-couplings in several C−C and C−E (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)−C(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)−C(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 Au•••H contacts in the solid state, the presence of Au•••H-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 β-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