NMR Signatures of the Active Sites in Sn-beta Zeolite

Dynamic nuclear polarization surface enhanced NMR (DNP-SENS), Mossbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active-site speciation in Sn-beta zeolite. This approach unambiguously shows the presence of framework Sn-IV-active sites in an octahedral environment, which probably correspond to so-called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework)

Hybrid polarizing solids for pure hyperpolarized liquids through dissolution dynamic nuclear polarization

Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by dissolution dynamic nuclear polarization (D-DNP) usually involves saturating the ESR transitions of polarizing agents (PAs; e.g., persistent radicals embedded in frozen glassy matrices). This approach has shown enormous potential to achieve greatly enhanced nuclear spin polarization, but the presence of PAs and/or glassing agents in the sample after dissolution can raise concerns for in vivo MRI applications, such as perturbing molecular interactions, and may induce the erosion of hyperpolarization in spectroscopy and MRI. We show that D-DNP can be performed efficiently with hybrid polarizing solids (HYPSOs) with 2,2,6,6-tetramethyl-piperidine-1-oxyl radicals incorporated in a mesostructured silica material and homogeneously distributed along its pore channels. The powder is wetted with a solution containing molecules of interest (for example, metabolites for MRS or MRI) to fill the pore channels (incipient wetness impregnation), and DNP is performed at low temperatures in a very efficient manner. This approach allows high polarization without the need for glass-forming agents and is applicable to a broad range of substrates, including peptides and metabolites. During dissolution, HYPSO is physically retained by simple filtration in the cryostat of the DNP polarizer, and a pure hyperpolarized solution is collected within a few seconds. The resulting solution contains the pure substrate, is free from any paramagnetic or other pollutants, and is ready for in vivo infusion

Palladium-catalyzed carbonylative cyclization via carbo- and acylpalladation of multiple bond systems

Under high pressure of CO, typically 40 atm, Palladium-catalyzed cyclization of $\omega$-vinyl iodobenzenes in the presence of MeOH provides an efficient synthesis of 5- and 6-membered ring $\beta$-keto-esters (Type II Ac-Pd). Di- and tricarbosubstituted alkenes react similarly, but premature esterification and Type I Ac-Pd can be serious competitive reactions. Nonetheless the use of less nucleophilic trapping agents and lower polarity solvents allows clean cyclization. Moreover, free hydroxyls are detrimental to the cyclization process, while protected, they give good yield of Type II Ac-Pd products and allow high level of asymmetric induction. Cyclization of iodo-dienes and -trienes provides an efficient synthesis of polycyclic structures via cascading cyclic acylpalladation. The use of carbon monoxide as a one carbon unit in a cascading process allows the novel angular-fused-mode cascade. In the related carbonylative cyclization of alkynes, Ac-Pd is restricted to the formation of 5-membered rings; while the intermolecular process provides an efficient synthesis of butenolides from the carbonylation of aryl iodides in the presence of internal alkynes. Cyclic carbopalladation is indeed more favored and usually overshadows the competitive acylpalladation process. This has allowed the development of zipper -mode and dumbbell -mode cascade carbopalladation of alkynes where termination has been effectively achieved via various carbonylative trapping processes such as esterification, amidation, C-enolate trapping, and carbonylative cyclization of alkenes. 1,1-Disubstituted alkenes can also participate in tandem carbopalladation-carbonylative esterification processes. In this case, carbopalladation generates a stereogenic carbon. The use of TBDMS protected hydroxyls gives high level of 1,4-asymmetric induction (85-99%) and provides an efficient diastereoselective synthesis of the Colvin-Raphael lacton. The related non-carbonylative zipper -mode process was used toward the diastereoselective synthesis of epi-$\alpha$-Vetivone

Fonctionnalisation d une silice avec des silanes de surface (de particules supportées de métaux des groupes 8-10 vers l obtention d hydrures mononucléaires)

Ru(COD)(COT) se greffe sur une silice fonctionnalisée avec des groupements SiMe2H par une liaison directe Si-Ru, qui empêche la formation de particules métalliques lors du traitement sous H2 à haute température (300/500 C) et conduit à la formation d hydrures mononucléaires ( SiO)SiMe2RuH3 (avec ( SiO)SiMe2RuCp à 300 C). Contrairement aux particules, ( SiO)SiMe2RuH3 hydrogène sélectivement les oléfines par rapport aux aromatiques, et hydrogénolyse les alcanes par des étapes élémentaires impliquant un seul centre métallique. Cette approche a également permis la préparation de clusters nus stabilisés par liaison Si-Ru, soit par le greffage de Ru3(CO)12 suivi d une étape de décarbonylation, soit par réactions successives de ( SiO)SiMe2RuH3 avec Ru( 3-C3H5)2(COD) suivies d étapes d hydrogénolyse. Finalement, le greffage de Pt(COD)2 sur les fonctionnalités SiMe2H suivi d une hydrogénolyse à 300 C conduit à la formation de composés trinucléaires [( SiO)SiH2PtHx]3. Cette stratégie conduisant à la formation de composés de faible nucléarité peut certainement être transposée à d autres métaux de transition des groupes 8-10Silica surfaces functionalised with silanes, e.g. SiMe2H groups, allow the grafting of Ru(COD)(COT) via a stable Si-Ru bond which avoids the growth of particles upon treatment under H2 up to 500 C, thus yielding ( SiO)SiMe2RuH3 (along with ( SiO)SiMe2RuCp at 300 C). Compared to ruthenium particles, ( SiO)SiMe2RuH3 selectively hydrogenates alkenes over aromatics, and catalyses the hydrogenolysis of alkanes with different elementary steps involving a single metal centre. Additionally, this approach was successfully used to generate bare clusters attached by Si-Ru bonds through either grafting of Ru3(CO)12 on SiMe2H groups followed by decarbonylation or successive reactions of ( SiO)SiMe2RuH3 with Ru( 3-C3H5)2(COD) followed by hydrogenolysis at high temperatures. Finally, trinuclear Pt species [( SiO)SiH2PtHx]3 was prepared by grafting of Pt(COD)2 on SiMe2H groups followed by hydrogenolysis at 300 C. This promising strategy yielding species of low nuclearity can be most probably extended to other late transition metalsLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Développement de catalyseurs hétérogènes à base de fer pour l'époxydation des oléfines

L'objectif de ce travail a été la synthèse de catalyseurs hétérogènes d'époxydation des oléfines. Actuellement cette réaction a été réalisée par des catalyseurs homogènes bio-inspirés et hétérogènes, conduisant ainsi à des procédés d'époxydation qui souffrent tous de problème de sélectivité et produisent une quantité énorme de sous produits. Au cours de ce travail, la préparation de nouveaux catalyseurs bien définis, à base de fer supportés sur oxydes, pour l'époxydation des oléfines a été abordée par la voie Chimie Organométallique de Surface. Plusieurs supports ont été sélectionnés (silice, SBA-15, alumine et silice-alumine). Trois types de précurseurs moléculaires (complexes organométalliques à base de Fer) sont utilisés : monomère stabilisé ou pas par un ligand et dimère. Leur greffage sur les différents supports ont permis d'obtenir trois classes différentes de catalyseurs: catalyseur monométallique avec ou sans ligand à base de Fer(II), catalyseur bimétallique à base de Fer(II) et catalyseur monométallique à base de Fer(III) dispersé sur support oxyde. Enfin l'activité de tous ces catalyseurs dans les réactions d'époxydation du cyclohéxène par H2O2 et du propène par N2O a été étudiée et un mécanisme d'oxydation a été proposé. Des activités intéressantes ont été obtenues, montrant ainsi la stratégie à adopter pour la prochaine génération de catalyseursLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Compréhension moléculaire de catalyseurs hétérogénes par résonance magnétique nucléaire du solide (vers une approche structure-réactivité en métathèses des Alcanes)

LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Conception de sondes et nano-sondes à base de lanthanides émettant dans le proche infrarouge pour la microscopie biphotonique

L objectif de cette thèse est l élaboration de sondes à base de lanthanide pour la microscopie optique biphotonique. Cette technique d imagerie complémentaire à l IRM et au scanner permet une analyse rapide et facile de tissus épais. Afin de permettre l observation en profondeur, l absorption et l émission de la sonde doit se situer dans la zone de transparence biologique [700 1200 nm]. L absorption à deux photons (ADP) est un phénomène d optique linéaire de troisième ordre par lequel l état excité est atteint par absorption simultanée de deux photons. De fait, l excitation à énergie moitié se situe dans la zone de transparence biologique. Les sondes envisagées combineraient les propriétés optiques uniques des lanthanides, telles que des bandes d émission très étroites allant du visible à l infrarouge et des durées de vie de luminescence longues, et les avantages de l ADP, permettant une excitation dans l IR et une résolution tridimensionnelle. Dans ce contexte, cette thèse décrit l élaboration de complexes d europium et d ytterbium à ligands macrocycliques stables en milieu aqueux et dont la luminescence peut être sensibilisée à deux photons. Ces complexes ont permis l imagerie de la vascularisation de cerveaux de souris par microscopie biphotonique dans le proche infrarouge. La seconde approche consiste à encapsuler un complexe luminescent dans des nanoparticules desilice formées par la technique sol-gel (collaboration A. Ibanez, institut Néel, Grenoble) afin de protéger le complexe du milieu biologique. Enfin la dernière approche consiste à greffer des complexes de lanthanides à la surface d une particule de silice par chimie organométallique de surface. Ces travaux ont conduit à la formation de nano-objet très brillants dans le rouge et le proche infrarouge, détectables à l échelle de l objet unique par microscopie à deux photons.Two Photon Scanning Laser Microscopy (TPSLM) has evolved as an emerging bio-imaging technique widely used in academic research and in medical diagnosis. This technique requires the design of bioprobes specially optimized for such purpose. A particular attention is actually devoted bio-probes featuring both two-photon absorption (TPA) and emission in the near infra-red (NIR) spectral range [700 1200 nm], also called biological window that is particularly promising for thick tissues imaging. In this context, europium complexes emitting in the red (615 nm) has been recently sensitized by two photon antenna effect and used for TPSLM in cells combining the advantages of lanthanide emission (sharp line and long lived) and those of TPA. Based on this preliminary results, this thesis describe the design of europium and ytterbium complexes which have an improved stability in water and good emission properties sensitized by TPA. Theses complexes allow the imaging of mice s brain vascularisation in the NIR. An another approach to stabilize lanthanide complexes was also used by encapsulating theses fluorophores in silica nanoparticle (collaboration with A. Ibanez, Institut Néel, Grenoble). Then the last approach consists on the grafting of the chromophores on silica sphere using surface organometallic chemistry methods. The nanoparticles obtained by both way are really luminescent in the red or infrared and can be imaged as single nanoparticle by TPSLM.LYON-ENS Sciences (693872304) / SudocSudocFranceF

High resolution solid state NMR spectroscopy in surface organometallic chemistry: access to molecular understanding of active sites of well-defined heterogeneous catalysts

Recent advances in solid state NMR spectroscopy have made possible the understanding of surface species and active sites of heterogeneous catalysts at a molecular level. This tutorial review describes solid state NMR spectroscopy, what are the possible techniques to obtain high resolution and 2D spectra ( structural information), and what are their applications in the context of well-defined heterogeneous catalysts prepared by surface organometallic chemistry

Probing surface site heterogeneity through 1D and INADEQUATE P-31 solid state NMR spectroscopy of silica supported PMe3-Au(I) adducts

Grafting of (Me3Si)(2)N-AuPMe3 on SiO2-(700) leads to the formation of [( SiO)Au-PMe3] located in different surface environments due to the presence or absence of adjacent siloxane bridges, as shown both by P-31 solid state NMR and by its conversion into a mixture of [( SiO)Au-PMe3] and [( SiO)Au(PMe3)(2)] upon exposure to PMe3

Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy

Many of the functions and applications of advanced materials result from their interfacial structures and properties. However, the difficulty in characterizing the surface structure of these materials at an atomic level can often slow their further development Solid-state NMR can probe surface structure and complement established surface science techniques, but its low sensitivity often limits its application. Many materials have low surface areas and/or low concentrations of active/surface sites. Dynamic nuclear polarization (DNP) is one Intriguing method to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude. In a DNP experiment, the large polarization of unpaired electrons is transferred to surrounding nuclei, which provides a maximum theoretical DNP enhancement of similar to 658 for H-1 NMR. In this Account, we discuss the application of DPIP to enhance surface NMR signals, an approach known as DNP surface enhanced NMR spectroscopy (DNP SENS). Enabling DNP for these systems requires bringing an exogeneous radical solution into contact with surfaces without diluting the sample. We proposed the incipient wetness impregnation technique (IWI) a well-known method in materials science, to impregnate porous and particulate materials with just enough radical containing solution to fill the porous volume. IWI offers several advantages: it is extremely simple, provides a uniform wetting of the surface, and does not increase the sample volume or substantially reduce the concentration of the sample. This Account describes the basic principles behind DNP SENS through results obtained for mesoporous and nanoparticulate samples impregnated with radical solutions. We also discuss the quantification of the overall sensitivity enhancements obtained with DNP SENS and compare that with ordinary room temperature NMR spectroscopy. We then review the development of radicals and solvents that give the best possible enhancements today. With the best polarizing mixtures, DNP SENS enhances sensitivity by a factor of up to 100, which decreases acquisition time by five orders of magnitude. Such enhancement enables the detailed and expedient atomic level characterization of the surfaces of complex materials at natural isotopic abundance and opens new avenues for NMR. To illustrate these improvements, we describe the successful application of DNP SENS to characterize hybrid materials, organometallic surface species, and metal-organic frameworks