Catherine C. Santini

Influence of the self-organization of ionic liquids on the size of ruthenium nanoparticles: effect of the temperature and stirring

The size of ruthenium nanoparticles is governed by the degree of self-organization of the imidazolium based ionic liquid in which they are generated from (η4-1,5-cyclooctadiene)(η6-1,3,5-cyclooctatriene)ruthenium: the more structured the ionic liquid, the smaller the size.

Organized 3D-alkyl imidazolium ionic liquids could be used to control the size of in situ generated ruthenium nanoparticles?

The synthesis of ruthenium nanoparticles, RuNPs from the organometallic complex (η4-1,5-cyclooctadiene)(η6-1,3,5-cyclooctatriene)ruthenium(0), Ru(COD)(COT) in various imidazolium derived ionic liquids, ILs: [RMIm][NTf2] (R = CnH2n + 1 with n = 2; 4; 6; 8; 10), and [R2Im][NTf2] (RBu) and [BMMIm][NTf2] has been performed, under 0.4 MPa of H2, at 25 °C or at 0 °C with or without stirring. A relationship between the size of IL non-polar domains calculated by molecular dynamics simulation and the RuNP size measured by TEM has been found, suggesting that the phenomenon of crystal growth is probably controlled by the local concentration of Ru(COD)(COT) and consequently is limited to the size of the non-polar domains. Moreover, the rigid 3D organization based on C2–H⋯anion bonding and chosen experimental conditions, could explain the non-aggregation of RuNPs.

Surface organometallic chemistry: some fundamental features including the coordination effects of the support

Abstract The study of the various kinds of reactions between organometallic complexes and the surfaces of inorganic oxides, metals or zeolites constitutes a new aspect of the coordination chemistry on surfaces. In this non-exhaustive and short review article, we would like to try to answer a few questions regarding this area of coordination (or organometallic chemistry) which may have some future impact in the field of catalysis. The questions that we would like to answer are the following: Are the basic rules of molecular organometallic and coordination chemistry valid when one tries to apply them to surfaces? One can wonder whether or not the functionalities which are present at the surface of an oxide, M x O y (M–OH groups, strained M–O–M groups and MO, aso) have a chemical reactivity which can be predicted on the basis of molecular chemistry. A few selected examples will be given about the reactivity of tin, rhenium or zirconium alkyls with the silanol groups of partially dehydroxylated silica. Can we obtain reliable and precise informations when some selected tools of surface science and molecular organometallic chemistry are applied simultaneously to elucidate the structure of surface organometallic fragments? One can reasonably expect that the way the surface organometallic fragments coordinate to the surface can be rationalized on the simple rules of coordination chemistry (electron counting, formal oxidation state). A few examples will be given regarding the surface structure of silica-supported zirconium hydrides or rhodium allyls. Is it possible that a well chosen surface organometallic fragment represents an intermediate in heterogeneous catalysis? If one can study the reactivity of a well chosen surface organometallic fragment, then one is in a position to demonstrate some elementary steps of heterogeneous catalysis. In this review we shall consider the surface reactivity of supported rhodium allyls or tin alkyls. What kind of mobility can we expect from surface organometallic fragments? In sharp contrast with discrete ligands of molecular chemistry, surfaces of oxides obviously provide a so called “pool of oxygens” which binds the surface organometallic fragments in a localized manner. However, due to its almost infinite structure, such a “pool” is obviously responsible for surface mobility, which is also a key parameter in certain catalytic processes (sintering, diffusion processes, reconstructions, leaching,⋯). Examples will be given on the mobility of Rh I (CO) 2 grafted onto a silica surface. The organometallic fragments are also mobile around the metal carbon bonds and this phenomenon can be evidenced by solid-state nuclear magnetic resonance (NMR) and can have applications in molecular separations and on the reactivity of the organometallic complexes. In each case, the role of the support as a coordinating ligand is a key factor of this chemistry.

Interaction between the π-System of Toluene and the Imidazolium Ring of Ionic Liquids: A Combined NMR and Molecular Simulation Study

The solute-solvent interactions and the site-site distances between toluene and ionic liquids (ILs) 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [BMMIm][NTf2] and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIm][NTf2] at various molar ratios were determined by NMR experiments (1D NMR, rotating-frame Overhauser effect spectroscopy (ROESY)) and by molecular simulation using an atomistic force field. The difference in behavior of toluene in these ILs has been related to the presence of H-bonding between the C2-H and the anion in [BMIm][NTf2] generating a stronger association (>20 kJ.mol-1) than in the case of [BMMIm][NTf2]. Consequently, toluene cannot cleave this H-bond in [BMIm][NTf2] which remains in large aggregates of ionic pairs. However, toluene penetrates the less strongly bonded network of [BMMIm][NTf2] and interacts with [BMMIm] cations.

Imidazolium ionic liquids as promoters and stabilising agents for the preparation of metal(0) nanoparticles by reduction and decomposition of organometallic complexes

The organometallic complexes ([Ru(COD)(2-methylallyl)2] and [Ni(COD)2] (COD=1,5-cyclooctadiene) dissolved in imidazolium ionic liquids (ILs) undergo reduction and decomposition, respectively, to afford stable ruthenium and nickel metal(0) nanoparticles (Ru(0)-NPs and Ni(0)-NPs) in the absence of classical reducing agents. Depending on the case, the reduction/auto-decomposition is promoted by either the cation and/or anion of the neat imidazolium ILs.

A novel stabilisation model for ruthenium nanoparticles in imidazolium ionic liquids: in situ spectroscopic and labelling evidence

In situ labelling and spectroscopic experiments are used to explain the key points in the stabilisation of ruthenium nanoparticles (RuNPs) generated in imidazolium-based ionic liquids (ILs) by decomposition of (eta(4)-1,5-cyclooctadiene)(eta(6)-1,3,5-cyclooctatriene)ruthenium(0), Ru(COD)(COT), under dihydrogen. These are found to be: (1) the presence of hydrides at the RuNP surface and, (2) the confinement of RuNPs in the non-polar domains of the structured IL, induced by the rigid 3-D organisation. These results lead to a novel stabilisation model for NPs in ionic liquids.

Formation and Characterization of Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph: (E)- and (Z)-[EtPhN+=CHCH2-B−(C6F5)3]

The stoichiometric reaction of B(C6F5)3 and NEt2Ph I, at room temperature, in an aromatic solvent, has been investigated by 1D and 2D NMR spectroscopy (1H, 11B,13C, 15N and 19F). No Et2PhN·B(C6F5)3 adduct was observed. An equilibrium between free B(C6F5)3, NEt2Ph, [HB(C6F5)3]−(HNEt2Ph)+ and two zwitterionic stereoisomers (E)- and (Z)-[EtPhN+=CH-CH2-B−(C6F5)3] (30%) in an E/Z ratio of 3:2 was observed. Whatever the protic reagent Z-OH [Z = H, SiPh3, (c-C5H9)7O12Si8, or silanol group of silica], all the equilibria involved in solutions of I are quantitatively displaced towards the ionic form [Z-O-B(C6F5)3]−(HNEt2Ph)+. In the case of dimethylaniline, besides free B(C6F5)3 and Me2NPh, the 1:1 adduct (C6F5)3B·NMe2Ph and an iminium salt [PhCH3N=CH2]+[HB(C6F5)3]− have been identified. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis and characterization of ionic liquids based upon 1-butyl-2,3-dimethylimidazolium chloride/ZnCl2

Trialkylimidazolium chlorozincate molten salts resulting from the combination of zinc chloride and 1-butyl-2,3-dimethylimidazolium chloride, [BMMI][Cl], have been prepared with a mole percent of ZnCl2, R (R = nZnCl2/nZnCl2 + n[BMMI][Cl]) equal to 0, 0.1, 0.25, 0.33, 0.5, 0.66, 0.75. Their analyses by DSC, 13C, 1H and 35Cl solid state and solution NMR, and mass spectrometry (ESI, MS/MS) are consistent with the presence of [BMMI][Cl] and [BMMI][ZnCl3] for R < 0.5; pure [BMMI][ZnCl3] for R = 0.5, and [BMMI][ZnCl3] with [BMMI][Zn3Cl7] for R > 0.5. Infrared spectra realized in the presence of pyridine show that the Lewis acidity of ZnCl2–[BMMI][Cl] increases with R. High temperature (110 °C) 13C and 35Cl NMR experiments on neat [BMMI][ZnCl3] (R = 0.5) evidenced that its structure varies with time from [BMMI][ZnCl3] to [BMMI⋯Cl⋯ZnCl2].

Continuous flow hydroformylation using supported ionic liquid phase catalysts with carbon dioxide as a carrier

A supported ionic liquid phase (SILP) catalyst prepared from [PrMIM][Ph(2)P(3-C(6)H(4)SO(3))] (PrMIM = 1-propyl-3-methylimidazolium), [Rh(CO)(2)(acac)] (acacH = 2,4-pentanedione) [OctMIM]NTf(2) (OctMIM = 1-n-octyl-3-methylimidazolium, Tf = CF(3)SO(2)) and microporous silica has been used for the continuous flow hydroformylation of 1-octene in the presence of compressed CO(2). Statistical experimental design was used to show that the reaction rate is neither much affected by the film thickness (IL loading) nor by the syngas:substrate ratio. However, a factor-dependent interaction between the syngas:substrate ratio and film thickness on the reaction rate was revealed. Increasing the substrate flow led to increased reaction rates but lower overall yields. One of the most important parameters proved to be the phase behaviour of the mobile phase, which was studied by varying the reaction pressure. At low CO(2) pressures or when N(2) was used instead of CO(2) rates were low because of poor gas diffusion to the catalytic sites in the SILP. Furthermore, leaching of IL and Rh was high because the substrate is liquid and the IL had been designed to dissolve in it. As the CO(2) pressure was increased, the reaction rate increased and the IL and Rh leaching were reduced, because an expanded liquid phase developed. Due to its lower viscosity the expanded liquid allows better transport of gases to the catalyst and is a poorer solvent for the IL and the catalyst because of its reduced polarity. Above 100 bar (close to the transition to a single phase at 106 bar), the rate of reaction dropped again with increasing pressure because the flowing phase becomes a better and better solvent for the alkene, reducing its partitioning into the IL film. Under optimised conditions, the catalyst was shown to be stable over at least 40 h of continuous catalysis with a steady state turnover frequency (TOF, mol product (mol Rh)(-1)) of 500 h(-1) at low Rh leaching (0.2 ppm). The selectivity of the catalyst was not much affected by the variation of process parameters. The linear:branched (l:b) ratios were ca. 3, similar to that obtained using the very same catalyst in conventional organic solvents.

Ruthenium nanoparticles in ionic liquids: structural and stability effects of polar solutes

Ionic liquids are a stabilizing medium for the in situ synthesis of ruthenium nanoparticles. Herein we show that the addition of molecular polar solutes to the ionic liquid, even in low concentrations, eliminates the role of the ionic liquid 3D structure in controlling the size of ruthenium nanoparticles, and can induce their aggregation. We have performed the synthesis of ruthenium nanoparticles by decomposition of [Ru(COD)(COT)] in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(1)C(4)Im][NTf(2)], under H(2) in the presence of varying amounts of water or 1-octylamine. For water added during the synthesis of metallic nanoparticles, a decrease of the solubility in the ionic liquid was observed, showed by nanoparticles located at the interface between aqueous and ionic phases. When 1-octylamine is present during the synthesis, stable nanoparticles of a constant size are obtained. When 1-octylamine is added after the synthesis, aggregation of the ruthenium nanoparticles is observed. In order to explain these phenomena, we have explored the molecular interactions between the different species using (13)C-NMR and DOSY (Diffusional Order Spectroscopy) experiments, mixing calorimetry, surface tension measurements and molecular simulations. We conclude that the behaviour of the ruthenium nanoparticles in [C(1)C(4)Im][NTf(2)] in the presence of 1-octylamine depends on the interaction between the ligand and the nanoparticles in terms of the energetics but also of the structural arrangement of the amine at the nanoparticles surface.