Isabelle Favier

A new and specific mode of stabilization of metallic nanoparticles

We report in this paper the stabilization of ruthenium nanoparticles using a very simple ligand (4-(3-phenylpropyl)pyridine), through strong pi-coordination of the phenyl moiety.

A Single Catalyst for Sequential Reactions: Dual Homogeneous and Heterogeneous Behavior of Palladium Nanoparticles in Solution

The design of synthetic strategies involving multistep processes in one-pot procedures is a key challenge for the fine chemical industry, in order to achieve ecologically and economically favorable production, taking into account the costs, the toxicity of solvents and the materials purification. 2] Multistep processes are defined as a sequence of reactions that are performed in one process without isolation or purification of any intermediates. 4] One group of such procedures comprises sequential processes where reagents are added and/or conditions are modified to initiate subsequent reactions. 6] For metal-catalyzed processes, the use of a single catalyst for different kinds of reactions is especially attractive. Metallic nanoparticles used as catalytic precursors in wet medium can behave as reservoirs of molecular species and can also have a surface-like reactivity, depending on the reaction conditions. 8] This “dual” catalytic behavior shows enormous potential in complex transformations for economizing purification steps. This approach is especially applicable to ionic liquid medium, due to the enhanced stability of the nanoclusters. Herein, we have studied a sequential Heck coupling and hydrogenation process, which uses palladium nanoparticles (PdNP) stabilized in ionic liquid (IL) as the sole catalytic precursors for sequential reactions. We prepared Pd nanoparticles (NPs) from two organometallic precursors in ionic liquid medium, following the methodology previously described (Scheme 1). 10] When [Pd(ma) ACHTUNGTRENNUNG(nbd)] (ma = maleic anhydride, nbd = norbornadiene) was used as molecular precursor, full decomposition was achieved at room temperature under 3 bar hydrogen pressure, whereas with [Pd2ACHTUNGTRENNUNG(dba)3] (dba = dibenzylideneacetone), the decomposition only occurred at higher temperature (60 8C), independently of the IL involved. Depending on the nature of the metallic precursor and the imidazolium-based IL used, different kinds of self-organization and dispersion of the PdNPs were observed by TEM (see the Supporting Information, Figure S1), probably due to the different interactions of the IL and the remaining ligands with the metallic surface, as supported by DOSY NMR spectroscopy. Palladium nanoparticles in [EMI] ACHTUNGTRENNUNG[MeO(H)PO2] (EMI = 1-ethyl-3-methylimidazolium) exhibit spherical shapes (mean diameter 4 nm), showing a trend to be assembled (Figure 1 a and Figure S1 d in the Supporting

Synthesis of Platinum–Ruthenium Nanoparticles under Supercritical CO2 and their Confinement in Carbon Nanotubes: Hydrogenation Applications

Bimetallic platinum–ruthenium nanoparticles stabilised by pyridine‐ and monophosphine‐based ligands were prepared either in supercritical CO2 or in THF. TEM analyses evidenced a tendency of the nanoparticles prepared in supercritical CO2 to agglomerate. Both types of bimetallic nanoparticles were further confined into functionalised multiwalled carbon nanotubes. Upon confinement, PtRu nanoparticles stabilised by phosphine ligands appeared more agglomerated than those stabilised by the pyridine ligand. These materials were applied to cinnamaldehyde hydrogenation. Confined PtRu nanoparticles showed higher catalytic activity and selectivity than unsupported nanoparticles.

Kinetico–mechanistic studies of C–H bond activation on new Pd complexes containing N,N′-chelating ligands

The hybrid imine/amine palladium(II) coordination complexes [PdX2(kappa2-N(imino),N(amino))](X = Cl, AcO; kappa2-N(imino),N(amino)= 4ClC6H4CHNCH2(CH2)nN(CH3)2, n= 1, 2) have been prepared in different isomeric forms which include E/Z arrangement around the C[double bond]N bond of the hybrid ligand and {Pd(kappa(2)-N(imino),N(amino))} ring conformation. The crystal structures of four of them, E-1AcO, Z-1AcO, E-2AcO and E-2Cl, have been determined and the solution behaviour in acetic acid, the common cyclometallating solvent, for all these systems studied. The complexes in acetic acid solution are shown to maintain the structure determined by X-ray crystallography, as they do in deuterated chloroform. Nevertheless, a partial opening equilibrium of the {Pd(kappa2-N(imino),N(amino))} ring is observed by NMR experiments. When the complexes are held in solution for longer periods the corresponding cyclometallated derivatives, 1AcO-CM, 2AcO-CM, 1Cl-CM and 2Cl-CM, containing the {Pd(kappa2-C,N(imino))} palladacycle are obtained, as characterized by 1H NMR spectroscopy. In these compounds the total opening of the N(amino) moiety of the ligand has occurred. The C-H bond activation process has been studied kinetico-mechanistically at different temperatures, pressures and acid concentrations; the results agree with the need of an opening of the chelate ring in [PdX2(kappa2-N(imino),N(amino))] prior to the proper cyclometallation reaction. The values of the enthalpies of activation are higher than those observed for known N-monodentated cyclometallating ligands, as should correspond to the contribution of a ligand dechelation pre-equilibrium. The entropies and volumes of activation are also indicative of this predissociation that include an important amount of contractive ordering. The presence of small amounts of triflic acid in the reaction medium accelerates the reaction to the value observed for N(imino)-monodentate systems, indicating that the full opening of the chelate ring has taken place. For the badly oriented isomeric forms of the ligand in the chelated complex (Z), the cyclometallation process is even more slow and corresponds directly to the reorganization of the ligand to its cyclopalladation-active (E) conformation.

Imidazolium-based ionic liquids immobilized on solid supports: effect on the structure and thermostability

[BMI][PF(6)] has been supported on silica and alumina in order to study the effect of these classical oxide supports on the structure of the ionic liquid. A widespread characterization by TGA, DSC, XRD and solid NMR of thin films of [BMI][PF(6)] immobilized on these amorphous supports has evidenced a dramatic effect on the ionic liquid structure depending on the nature of the support. For the alumina composite, a loss of the supramolecular arrangement of the ionic liquid occurs, while for the analogous silica composite, ions interact strongly with the support, leading to a [BMI][PF(6)] thermostability decrease.

Glycerol as Suitable Solvent for the Synthesis of Metallic Species and Catalysis

This Minireview considers the foremost reported works involving glycerol as a solvent in the synthesis of organometallic complexes and metallic nanoparticles. This analysis highlights their catalytic applications. A special emphasis is devoted to the ability of glycerol to immobilize nanometric species, which, in turn, enables an efficient recycling of the catalytic phase to give metal-free organic products.

A smart palladium catalyst in ionic liquid for tandem processes

New catalytic systems based on in situ and preformed palladium nanoparticles in ionic liquids (characterised by TEM) starting from palladium acetate or dipalladiumtris(dibenzylideneacetone) have been applied in the synthesis of 4-phenylbutan-2-one (II), a model compound for the preparation of fragrances. Imidazolium-based ionic liquid containing a methyl hydrogenophosphonate anion leads to an efficient Pd-catalyzed tandem coupling/reduction process, taking advantage of the multi-role of this solvent (nanoparticles stabiliser, base, hydrogen transfer agent). The influence of the mono-phosphine ligands (1-3) on the catalyst has been evaluated, showing that the ligand-free palladium system turns into the most appropriate for the formation of II using Pd(OAc)(2) as precursor. Fine-tuning conditions involved in this multi-parameter process have led us to propose a plausible mechanism based on the hydrogen transfer coming from the methyl hydrogenophosphonate anion.

Hydrogenation Processes at the Surface of Ruthenium Nanoparticles: A NMR Study

AbstractThe reactivity of ruthenium nanoparticles stabilized by 4-(3-phenylpropyl)pyridine in hydrogen transfer and hydrogenation processes was monitored by NMR spectroscopy. Unsaturated substrates such as styrene, 4-vinylpyridine and 4-phenyl-but-3-en-2-one were used as model molecules to investigate the surface properties of nanoparticles by a combination of NMR studies. Interestingly, the hydrides present at the metallic surface after nanoparticles synthesis are selectively transferred to vinylic groups without reducing the aromatic rings, under dihydrogen-free atmosphere. DOSY and NOE NMR experiments permitted to propose a way of interaction of the organic compounds at the metallic surface. In particular, the coordination of the substrate could be evidenced for 4-vinylpyridine and 4-ethylpyridine but not for styrene derivatives.Graphical AbstractCurved double arrows represent magnetization exchanges. Straight arrows represent adsorption/desorption phenomena.

Membrane Reactor Based on Hybrid Nanomaterials for Process Intensification of Catalytic Hydrogenation Reaction: an Example of Reduction of the Environmental Footprint of Chemical Synthesis from a Batch to a Continuous Flow Chemistry Process

Membrane processes represent a well matured technology for water treatment with low environmental footprints compared to other type of processes. We have now combined this technology with nanomaterials, ionic liquids (negligible vapor pressure), and poly(ionic liquids) in order to enlarge the field of applications while benefiting from the advantages of membranes. We have modified flat sheet water filtration membrane and used it as both catalytic support and reactor with the advantages to make the reaction and the separation of products in only one step. For this purpose, catalytic metallic nanoparticles of palladium (diameter of ca. 2 nm) were synthesized in a gel-poly(ionic liquid) layer grafted at the surface of polymeric filtration membranes by UV-photografting method. The so obtained catalytic membrane was successfully applied in the hydrogenation of trans-4-phenyl-3-buten-2-one in forced flow-through configuration, which gave full conversion in a few seconds (2.6 s) showing advantages over the batch reactor process (in that case, palladium nanoparticles were synthesized in the ionic liquid [MMPIM][NTf2] (1,2-dimethyl-3-propylimidazolium bis-(trifluoromethylsulfonyl)imide)). Nevertheless, the catalytic membrane used in submerged mode no more prevailed over the batch reactor. Catalytic nanoparticles remain highly active in the membrane after 12 cycles of reaction without need of recuperation. Results were compared to one obtains with a similar system in batch reactor conditions, showing high efficiency of our process in term of selectivity and reactivity, combined to an important compactness, the productivity of the catalytic hollow fiber membrane reactor and permitting to operate at larger scale with promising results in an environmental friendly way in term of energy and product (metal, solvent) consuming.