Modélisation de nanoparticules produites par voie organométallique et de catalyseurs greffés : structure, spectroscopie, réactivité

L'étude présentée dans cette thèse se situe dans le cadre des études de la chimie de surface de nanoparticules (NPs) de ruthénium d'une part et de la chimie de surface de silice servant de support à des complexes organométalliques d'autre part. Ce travail est divisé en deux parties, chacune d'entre elles étant fondée sur une des questions suivantes : Où sont coordinnés les atomes d'hydrogène sur les surfaces de nanoparticules de ruthénium et quel effet ont les ligands sur ces atomes ? La synthèse de NPs dont la taille, la forme et la composition pourraient être contrôlées de façon précise présente un grand intérêt en science des matériaux. Leurs propriétés physico-chimiques à l'interface entre les petits composés moléculaires et les solides massifs sont un des meilleurs atouts des ces NPs. Les NPs possèdent une chimie de surface extrêmement riche et assez peu étudiée qui peut influencer aussi bien les propriétés chimiques que physiques. Dans notre cas, nous nous sommes particulièrement intéressés aux atomes d'hydrogène qui jouent un rôle essentiel, aussi bien sur la taille que sur la forme de ces NPs, mais dont le mode de coordination reste inconnu. Pour répondre à cette première question, les NPs ont été modélisées par deux systèmes qui encadrent le domaine de taille de celles-ci : des agrégats de petite taille et des surfaces périodiques. L'étude conjointe de ces deux systèmes nous a permis, via la comparaison théorie/expérience de plusieurs données spectroscopiques comme la RMN du proton ou du deutérium ainsi que des données infra rouges, de déterminer la coordination la plus probable de ces atomes ainsi que l'effet des ligands de surface sur eux. Comment des catalyseurs organométalliques sont ils greffés sur une surface de silice lors des réactions de catalyse supportée et quel est l'impact du greffage sur leurs réactivité ? L'importance de la catalyse aussi bien d'un point de vue économique (industriel) que pour le respect de l'environnement exige l'utilisation de catalyseurs de plus en plus performants. Une des approches possibles pour atteindre cet objectif est d'avoir une meilleure distribution et définition des sites actifs pour des réactions en catalyse hétérogène. Une des façons d'obtenir ce contrôle est la catalyse supportée. Cependant, un des prérequis pour ce type de catalyse est de connaître de façon précise les différents types d'interactions entre le catalyseur et le support. Néanmoins, dans le cas d'un catalyseur organométallique à base de lanthanide greffé sur un surface de silice, le mode de greffage est complètement inconnu. Comme pour l'étude précédente, il existe deux possibilités pour traiter ce problème : soit par une approche périodique, soit par une approche moléculaire. Dans ce cas, l'étude conjointe des deux approches n'est pas nécessaire. En effet, diverses considérations nous ont amenés à choisir une approche moléculaire afin de mener à bien cette étude. Pour cela, nous avons dû créer un modèle moléculaire qui représente le plus fidèlement possible les surfaces de silice. La réaction de greffage à été ensuite étudiée sur ce modèle donnant naissance à différents modes de greffage, répondant ainsi aux interrogations émises par les expérimentateurs. Finalement, une comparaison entre différentes réactions catalytiques ayant lieu avec un complexe metallocénique à base de lanthanide a également été menée avec le catalyseur greffé afin de comparer la réactivité de ces deux systèmes et de déterminer le rôle de la surface sur la réactivité du catalyseur.The work presented in this PhD manuscript concerns the study of surface chemistry and it is based on two questions asked by different experimental research groups. These questions cover different areas of surface chemistry, their answer would lead to a better understand the interactions occurring on these surfaces. This work is divided into two parts, each of which are based on the following issues: In which positions are the hydrogen atoms coordinated on the surface of ruthenium nanoparticles and which effect have the ligands on these atoms? It is of great interest in materials science to be able to control the size, shape and composition of nanoparticles (NPs) during their synthesis process. Their physico-chemical properties, comprised between those exhibited by small molecular compounds and the bulk, are one of the best advantages of these NPs. The NPs have an extremely rich surface chemistry, relatively little studied, that may influence both their chemical and physical properties. In this study, we are particularly interested in hydrogen atoms that play a key role in both the size and the shape of the NPs. However, their coordination mode remains unknown. To answer this first question, the NPs were modeled by two limit systems : small clusters and periodic surfaces. The study of these two systems allowed us, through a theory / experiments comparison of several spectroscopic data such as proton, deuterium NMR and infrared data to determine the most likely coordination mode of these hydrogen atoms and the effect of ligands on them. How organometallic catalysts are they grafted on a silica surface during catalytic supported reactions and which is the impact of the grafting mode on their reactivity ? The importance of catalysis both from an economic perspective (industrial) and environmental perspectives, requires the use of more efficient catalysts. One approach to achieve this goal is to have a better distribution and definition of active sites involved in heterogeneous catalysis process. One possibility to achieve this control is the use of supported catalysis. However, a prerequisite for this type of catalysis includes precise knowledge of the different types of interactions existing between the catalyst and its support. However, in the case of a lanthanide catalyst grafted on silica surface, the grafting mode remains unknown. As in the previous study, there are two methods to address this problem: either by a periodic approach, either by a molecular approach. Several different considerations led us to choose a molecular approach to conduct this study. For that purpose, we have created a molecular model that represents as accurately as possible the silica surface. The grafting reaction was then studied on this model, giving rise to different grafting modes, which are in accordance with the experimental data. Finally, a comparison between different catalytic reactions taking place with a metallocene lanthanide complex and the grafted catalyst above described has also been undertaken. Throught this investigation we could compare the reactivity of these two systems and determine the role of surface on the catalyst reactivity

On the interaction of phosphines with high surface area mesoporous silica

To increase the efficiency and selectivity of homogeneous catalysts, particularly useful in the synthesis of fine chemicals and drugs, fine tuning of the steric and electronic properties of the complexes can be achieved by modification of the ligands in the coordination sphere of the metal center. Considerable efforts have been devoted in order to immobilize such well-defined catalysts on solid substrates, e.g., silica, to facilitate catalysts’ recovery and to reduce contamination of desired products by metallic impurities. However, the presence of the silica surface can play a very important role in tuning the electronic properties of the metal, its steric environment, or in participating in the reactivity of the complex. In this context, several moieties have been used to anchor metallic catalysts on surfaces, but one of the most interesting is phosphine. Herein, we report on the addition of PPh2Cl which leads to the grafting and the oxidation of the phosphine species, even in absence of oxygen, and that the nature of the surface plays an important role in secondary interactions, e.g., hydrogen bonding, and modifies the spectroscopic properties of the functional groups on the surface. In particular, the chemical shift of the phosphorous resonance in the P NMR spectra is altered by hydrogen bonding between available silanol or water molecules present on the silica surface and the phosphorous oxide. The DFT models developed for this process are in direct accordance with the experimental results and demonstrate firmly that the oxidation of the phosphine after grafting of ClPR2 is highly favored thermodynamically and occurs with the formation of Si-Cl bonds on the surface. Passivation of the surface with hexamethyldisilazane limits the extent of the H-bonding between the surface and the oxide, but also leads to some substitution reaction between bound phosphorous species and the trimethylsilyl (TMS) moieties. These findings offer new knowledge critical to fully ascertain the environment and the stability of immobilized phosphine-containing catalytic systems and, thus, further broaden the range of their reactivity

CO 2 cleavage by tantalum/M (M = iridium, osmium) heterobimetallic complexes

A novel Ta/Os heterobimetallic complex, [Ta(CH2tBu)3(μ-H)3OsCp*], 2, is prepared by protonolysis of Ta(CHtBu)(CH2tBu)3 with Cp*OsH5. Treatment of 2 and its iridium analogue [Ta(CH2tBu)3(μ-H)2IrCp*], 1, with CO2 under mild conditions reveal the efficient cleavage of CO2, driven by the formation of a tantalum oxo species in conjunction with CO transfer to the osmium or iridium fragments, to form Cp*Ir(CO)H2 and Cp*Os(CO)H3, respectively. This bimetallic reactivity diverges from more classical CO2 insertion into metal-X (X = metal, hydride, alkyl) bonds

3D Ruthenium Nanoparticle Covalent Assemblies from Polymantane Ligands for Confined Catalysis

The synthesis of metal nanoparticle (NP) assemblies stabilized by functional molecules is an important research topic in nanoscience, and the ability to control interparticle distances and positions in NP assemblies is one of the major challenges in designing and understanding functional nanostructures. Here, two series of functionalized adamantanes, bis-adamantanes, and diamantanes, bearing carboxylic acid or amine functional groups, were used as building blocks to produce, via a straightforward method, networks of ruthenium NPs. Both the nature of the ligand and the Ru/ligand ratio affect the interparticle distance in the assemblies. The use of 1,3-adamantanedicarboxylic acid allows the synthesis of three-dimensional (3D) networks of 1.7–1.9 nm Ru NPs presenting an interparticle distance of 2.5–2.7 nm. The surface interaction between Ru NPs and the ligands was investigated spectroscopically using a 13C-labeled ligand, as well as theoretically with density functional theory (DFT) calculations. We found that Ru species formed during the NP assembly are able to partially decarbonylate carboxylic acid ligands at room temperature. Decarbonylation of a carboxylic acid at room temperature in the presence of dihydrogen usually occurs on catalysts at much higher temperatures and pressures. This result reveals a very high reactivity of ruthenium species formed during the network assembly. The Ru NP networks were found to be active catalysts for the selective hydrogenation of phenylacetylene, reaching good selectivity toward styrene. Overall, we demonstrated that catalyst activity, selectivity, and NP network stability are significantly affected by Ru NP interparticle distance and electronic ligand effects. As such, these materials constitute a unique set that should allow a better understanding of the complex surface chemistry in carbon-supported metal catalysts

Modélisation de nanoparticules produites par voie organométallique et de catalyseurs greffés (structure, spectroscopie, réactivité)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Shape, electronic structure and steric effects of organometallic nanocatalysts: relevant tools to improve the synergy between theory and experiment

bibtex: ISI:000391726400010 bibtex\location:'THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND',publisher:'ROYAL SOC CHEMISTRY',type:'Article',affiliation:'Poteau, R (Reprint Author), Univ Toulouse, INSA, UPS, CNRS,LPCNO IRSAMC, 135 Ave Rangueil, F-31077 Toulouse, France. Cusinato, Lucy; del Rosal, Iker; Poteau, Romuald, Univ Toulouse, INSA, UPS, CNRS,LPCNO IRSAMC, 135 Ave Rangueil, F-31077 Toulouse, France.','author-email':'[email protected]',da:'2018-12-05','doc-delivery-number':'EH4FH',eissn:'1477-9234','funding-acknowledgement':'ANR-DFG [MOCANANO 2011-INTB-1011-1]; HPCs CALcul en MIdi-Pyrenees (CALMIP-EOS) [P0611, P1415]; Grand Equipement National de Calcul Intensif (GENCI-TGCC) [6211]','funding-text':'We thank Drs K. Philippot and B. Chaudret for all our fruitful discussions these ten last years. We acknowledge financial support from the ANR-DFG (MOCANANO 2011-INTB-1011-1) project as well as the HPCs CALcul en MIdi-Pyrenees (CALMIP-EOS, grants P0611 and P1415) and the Grand Equipement National de Calcul Intensif (GENCI-TGCC, grant 6211) for generous allocations of computer time.','journal-iso':'Dalton Trans.','keywords-plus':'BRILLOUIN-ZONE INTEGRATIONS; FINNIS-SINCLAIR POTENTIALS; TOTAL-ENERGY CALCULATIONS; WAVE BASIS-SET; RUTHENIUM NANOPARTICLES; PLANE-WAVE; 1ST-PRINCIPLES CALCULATIONS; ADSORPTION PROPERTIES; COORDINATION NUMBERS; RU NANOPARTICLES','number-of-cited-references':'123','orcid-numbers':'Poteau, Romuald/0000-0003-4338-174X Del Rosal, Iker/0000-0001-6898-4550','research-areas':'Chemistry','researcherid-numbers':'Poteau, Romuald/F-7052-2011 Del Rosal, Iker/H-3419-2012','times-cited':'1','unique-id':'ISI:000391726400010','usage-count-last-180-days':'6','usage-count-since-2013':'34','web-of-science-categories':'Chemistry, Inorganic & Nuclear'\International audienceWorking closely with experimentalists on the comprehension of the surface properties of catalytically active organometallic nanoparticles (NPs) requires the development of several computational strategies which significantly differ from the cluster domain where a precise knowledge of their optimal geometry is a mandatory prerequisite to computational modeling. Theoretical simulations can address several properties of organometallic nanoparticles: the morphology of the metal core, the surface composition under realistic thermodynamic conditions, the relationship between adsorption energies and predictive descriptors of reactivity. It is in such context that an integrated package has been developed or adapted in our group: (i) one tool aims at building a wide variety of the typical shapes exhibited by nanoparticles. Using Reverse Monte Carlo modeling, a given shape can be optimized in order to fit pair distribution function data obtained from X-ray diffraction measurements; (ii) trends in density functional theory (DFT) adsorption energies of surface species can be rationalized and predicted by making use of simple descriptors. This is why we have proposed an extension of the d-band center model, that leads to the formulation of a generalized ligand-field theory. A comparison between cobalt and ruthenium is proposed in the case of a 55-atoms nanocluster. The accuracy of the generalized coordination number [ Angew. Chem., Int. Ed., 2014, 53, 8316], a very simple coordination-activity criterion, is also assessed; (iii) the builder package is completed by the steric-driven grafting of ligands on the surface of metal NPs. It easily generates structures with adjustable surface composition values and coordination modes; (iv) after a local optimization at the DFT level of theory, DFT energies and normal modes of vibration can feed a general tool based on the ab initio thermodynamics method. This method aims at easily calculating an optimal surface composition under realistic temperature and pressure conditions. In addition to that, we also show to what extent knowledge of the density of states (DOS) and of the crystal overlap Hamilton population (COHP), both projected from a plane-wave basis set to a local basis set, sheds light on metal core-ligand chemical bonding

Grafting of lanthanide complexes on silica surfaces dehydroxylated at 200 °C: a theoretical investigation

International audienceCluster models of SiO2-200 are proposed and compared with spectroscopic (IR and NMR) experimental data. Five models describing the variety of surface silanols (isolated, vicinal and germinal) at the SiO2-200 surface have then been derived and used to study the grafting reaction of homoleptic silylamide lanthanum(III) complexes. Three different grafting modes have been obtained (mono-, bi- and tri-grafted) in line with the experimental knowledge. In terms of energetic stability as well as spectroscopic properties of coordinated OPPh3 (as a probe), all modes could coexist at the surface. The analysis of the δ(31P) chemical shifts for the coordinated OPPh3 indicates some possible important differences in Lewis acidity of the lanthanide centre, which may impact the catalysis

Ligand-Field Theory-Based Analysis of the Adsorption Properties of Ruthenium Nanoparticles

International audienceThe experimental design of improved nanocatalysts is usually based on shape control and is surface-ligand dependent. First-principle calculations can guide their design, both in terms of activity and selectivity, provided that theoretical descriptors can be defined and used in a prescreening process. As a consequence of the Sabatier principle and of the Brønsted–Evans–Polanyi relationship, an important prerequisite before optimizing the catalytic properties of nanoparticles is the knowledge of the selective adsorption strengths of reactants at their surface. We report here adsorption energies of X (H, CH3) and L (PH3, CO) ligands at the surface of bare ruthenium nanoclusters Run (n = 55 and 147) calculated at the DFT level. Their dependence on the topology of the adsorption sites as well as on the size and shape of the nanoparticles (NPs) is rationalized with local descriptors derived from the so-called d-band center model. Defining the descriptors involves the determination of the energy of effective d atomic orbitals for each surface atom. Such a ligand field theory-like model is in close relation with frontier molecular orbital theory, a cornerstone of rational chemical synthesis. The descriptors are depicted as color maps which straightforwardly yield possible reactivity spots. The adsorption map of a large spherical hcp cluster (Ru288) nicely confirms the remarkable activity of steps, the so-called B5 sites. The predictive character of this conceptual DFT approach should apply to other transition metal NPs and it could be a useful guide to the design of efficient nanocatalysts bearing sites with a specific activity

Supported lanthanide catalysts: Role of the grafting on the stereochemical outcome of beta-butyrolactone ROP reaction

Fall National Meeting and Exposition of the American-Chemical-Society (ACS), San Diego, CA, AUG 25-29, 201

Effects of the Grafting of Lanthanum Complexes on a Silica Surface on the Reactivity: Influence on Ethylene, Propylene, and 1,3-Butadiene Homopolymerization

In this contribution, we report full details of the ethylene, 1,3-butadiene, and propylene homopolymerization processes mediated by alkylated bis­(trimethyl)­silylamide lanthanide-grafted complexes using a density functional theory (DFT) study of the initiation and first propagation steps. These systems allows us (i) to examine the role of the grafting mode on the kinetics and thermodynamics of the three processes considered, (ii) to confirm the catalytic behavior of these grafted complexes in ethylene polymerization, (iii) to rationalize the experimental preference for 1,4-cis polymerization of 1,3-butadiene, and (iv) to provide unprecedented information on the catalytic activity of the lanthanide-grafted complex as a propylene hompolymerization catalyst