La série "au cheval et au triskèle" : un nouveau monnayage d’origine santone ?

Cet article s’intéresse à un monnayage méconnu n’ayant pas encore fait l’objet d’une étude spécifique. Ces petites pièces, qui présentent au revers un cheval surmonté d’un triskèle, ont été tantôt attribuées aux Arvernes, aux Santons, au centre-ouest de la Gaule ou à l’actuel département de la Gironde... Il était donc nécessaire de procéder à une première synthèse afin d’en préciser la localisation et la chronologie. La recherche, fondée sur la documentation publiée, sur les collections publiques et sur le matériel issu de fouilles archéologiques, permet d’appréhender ce monnayage sous un oeil nouveau. Il est désormais possible de situer son émission autour de l’estuaire girondin et de la plaine charentaise, à l’orée de la période gallo-romaine.En este artículo se examina una emisión monetaria desconocida cuyo reverso representa un caballo con un trisquel encima y una voluta por debajo. Dichas monedas fueron atribuidas sucesivamente a los Arvernos, a los Santones, a poblaciones que vivían en el centro-oeste de la Galia o en el actual departamento de la Gironde… La confusión que rodea estas acuñaciones justifica la realización de una primera síntesis con el objetivo de precisar su localización y su cronología. La investigación se basa en la documentación publicada, las colecciones de museos y el material procedente de excavaciones arqueológicas. De aquí en adelante se podrá situar la producción de estas monedas alrededor del estuario de la Gironde, en los años posteriores a la conquista romana.Hiriart Eneko, Geneviève Vincent, Mauduit Thierry, Lefrais Yannick. La série “au cheval et au triskèle”, un nouveau monnayage d’origine santone ?. In: Aquitania : une revue inter-régionale d'archéologie, tome 34, 2018. pp. 117-134

Directed ortho C-H borylation catalyzed using Cp*Rh(iii)-NHC complexes

International audienceCp*Rh(NHC) complexes with bulky chiral bidentate NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. These unprecedented rhodium(iii) complexes demonstrated high selectivity in pyridine-directed ortho-C-H borylation of arenes under mild conditions

Visible Light Induced Rhodium(I)-Catalyzed C-H Borylation

International audienceAn efficient visible light induced rhodium(I)-catalyzed regioselective borylation of aromatic C-H bonds is reported. The photocatalytic system is based on a single NHC-Rh complex capable of both harvesting visible light and enabling the bond breaking/forming at room temperature. The chelating nature of the NHC-carboxylate ligand was critical to ensure the stability of the Rh complex and to provide excellent photocatalytic activities. Experimental mechanistic studies evidenced a photooxidative ortho C-H bond addition upon irradiation with blue LEDs, leading to a cyclometalated Rh -hydride intermediate

Gas bubble nucleation of extra-heavy oils in porous media : a new computerized and physical approach

International audienceThe study of multiphase flow pore level physic has scientific appeal as well as many applications, mainly in oil reservoir engineering. In this work, we show that micro-tomography is an effective tool to extract the structure of many solid systems in a non-destructive and classical manner. Recently, X-ray computed tomography tools have been extended to the ability to contrast fluids in the pore space of core samples. As time required for collecting a CT image is much longer than almost flow time scales, CT imaging must occur at static flow conditions to accurate geometrical information on fluid-fluid and solid - fluid interaction. Considering new decisive developments of the visualization cell we claim to have developed a new petrophysical tool which might permit to access experimentally to the visualization in quasi-static flow of the capillary phenomena and multiphase flows analysis in 3D form or in dynamic flow in 2D form. The in-situ measurements are realized in reservoir conditions of extra-heavy oils. The aim of the measurements is first to contribute to a predictive bubble population balance which will then be integrated in a network flow model computation. This step is required to develop physical models to obtain a more efficient reservoir simulation. More precisely we focus our attention on a quasi static model of bubble nucleation which appears decisive and we demonstrate how to simulate the whole bubble nucleation and the corresponding experimental results to corroborate the experimental observations. We focus here on the influence of the gas availability in the porous media (diffusivity, GOR or porous media morphology). Copyright 2007, Society of Petroleum Engineers

Readily Accessible Unsymmetrical Unsaturated 2,6-Diisopropylphenyl N-Heterocyclic Carbene Ligands. Applications in Enantioselective Catalysis

International audienceA new multicomponent procedure was applied to the synthesis of (a)chiral bulky unsymmetrical unsaturated 2,6-diisopropylphenyl N-heterocyclic carbene (NHC) precursors with excellent selectivity (up to 95%) and good yields. This approach offers access to new chiral NHC ligands, which have found successful applications in both copper-catalyzed asymmetric allylic alkylation and copper-catalyzed asymmetric borylation

Activation of olefin metathesis complexes containing unsymmetrical unsaturated N-heterocyclic carbenes by copper and gold transmetalation

International audienceThe activation of ruthenium-indenylidene complexes containing two unsymmetrical unsaturated N-heterocyclic carbenes (u2-NHCs) by a transmetalation process is reported. The use of copper(i) or gold(i) chlorides promotes the rapid trapping of one NHC ligand, which releases the catalytically active Ru-species. Impressive initiation rates with full-conversions are observed within one minute. This practical protocol demonstrates excellent catalytic performances in various ring-closing metathesis (RCM) and self-metathesis (SM) reactions

Ruthenium–NHC complex-catalyzed P( iii )-directed C–H borylation of arylphosphines

International audience(NHC)(arene)Ru(II) complexes with bidentate LX-type NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. The strong coordination of the NHC carboxylate ligand and the labile character of the arene ligand are highlighted. These unprecedented Ru(II) complexes demonstrated efficient catalytic activities in the selective P(III)-directed C–H borylation at the ortho position of arylphosphines, representing the first report of the use of a ruthenium–NHC based catalyst in C–H borylation

The debut of chiral cyclic (alkyl)(amino)carbenes (CAACs) in enantioselective catalysis

International audienceThe popularity of NHCs in transition metal catalysis has prompted the development of chiral versions as electron-rich neutral stereodirecting ancillary ligands for enantioselective transformations. Herein we demonstrate that cyclic (alkyl)(amino)carbene (CAAC) ligands can also engage in asymmetric transformations, thereby expanding the toolbox of available chiral carbenes

The debut of chiral cyclic (alkyl)(amino)carbenes (CAACs) in enantioselective catalysis.

The popularity of NHCs in transition metal catalysis has prompted the development of chiral versions as electron-rich neutral stereodirecting ancillary ligands for enantioselective transformations. Herein we demonstrate that cyclic (alkyl)(amino)carbene (CAAC) ligands can also engage in asymmetric transformations, thereby expanding the toolbox of available chiral carbenes

A kinetic resolution strategy for the synthesis of chiral octahedral NHC-iridium(III) catalysts

International audienceThe transmetalation reaction of a chiral-bidentate NHC-silver complex to racemic [Ir(-Cl)(ppy)2]2 operates with kinetic resolution leading to chiral octahedral NHC-iridium(III) complexes and enantio-enriched bis-cyclometalated iridium(III) complexes. The iridium(III) complexes demonstrated efficient catalytic activities in intermolecular [2+2] photocycloaddition reactions and in asymmetric Friedel-Crafts alkylations, respectively. In the past two decades, bis-cyclometalated Iridium(III) complexes have been attracting broad interest due to their outstanding photophysical and chemical properties which are ideal in view of applications in photonic and optoelectronic devices, 1 in bioimaging and cancer therapy as potential theranostic agents 2 and in organic synthesis as photosensitizer and photoredox catalysts. 3 More recently, particular attention has been given to N-Heterocyclic Carbenes (NHCs) ligands in the design of highly stable luminescent cyclometalated iridium complexes with high range of emission colors. 4 On the other hand, increasing efforts has been given to the development of efficient methods for the preparation of chiral octahedral Ir(III) complexes that are highly valuable materials to access selective protein inhibitors, circularly polarized (CP) light-emitting devices and chiral photocatalysts. 5 Nevertheless, there is still a need for efficient and practical strategies to synthesize chiral non racemic luminescent NHC-based octahedral Ir(III) complexes. 4c,l,6 Recently, we described a practical multicomponent strategy that provides access to various unsymmetrical NHC ligands precursors, including carboxyalkyl-NHCs that are beyond reach otherwise. 7 NHC ligands containing an additional donor functionality have demonstrated significant benefit in stabilizing a variety of transition-metal complexes. 8 Herein, we describe an efficient strategy for the synthesis of robust chiral luminescent octahedral NHC-iridium(III) complexes and enantio-enriched bis-cyclometalated iridium(III) complexes (Fig. 1). The catalytic potential of the new complexes was respectively demonstrated in a selective [2+2] photocycloaddition reaction and in asymmetric Friedel-Crafts alkylation. Fig. 1 Synthesis of chiral octahedral Iridium complexes. The reaction of racemic [Ir(-Cl)(ppy)2]2 (1) with the chiral NHC-Ag (S)-2 complex in dichloromethane at 40 °C afforded a mixture of the -(S) and -(S) diastereomers with a diastereomeric ratio of 2:1 in favor of the -(S)-3 as determined by 1 H NMR spectroscopy (Scheme 1, Fig. S1, ESI ‡). The strong -donor ability and chelating coordination mode of the chiral NHC-carboxylate ligand conferred high complex stability, 9 allowing efficient separation of the two diastereomers by silica gel chromatography to provide pure -(S)-3 and -(S)-4 in a good 75% combined isolated yields (49 and 26% respectively). Similar results were obtained when reacting racemic [Ir(-Cl)(ppy)2]2 (1) with the chiral NHC-Ag (R)-2 complex of opposite configuration, affording the mirror-imaged diastereomeric pair which was isolated (80% yield) in about 2:1 ratio in favor of the -(R)-3. The absolute configuration at the metal center of the new octahedral NHC complexes was confirmed by X-ray diffraction analysis of single crystals (Fig. 2). Both -(S)-3 and -(S)-4 diastereomers displayed strong structural similarity with high steric crowding around the Ir center. A typical ligand arrangement is observed with the pyridine N atoms of the ppy ligands lying in trans to each other, whereas the two ortho-carbons are respectively in trans to the carbenic carbon and in trans to the carboxylate fragment of the NHC ligand. The main structure difference results from the isobutyl substituent of the asymmetric carbon center that induces enhanced steric constraints in the -(S) conformation by pointing towards the pyridyl ligand