Bastien Léger

Supramolecular shuttle and protective agent: a multiple role of methylated cyclodextrins in the chemoselective hydrogenation of benzene derivatives with ruthenium nanoparticles

Efficient chemoselectivities have been obtained in the hydrogenation of benzene derivatives under biphasic liquid-liquid conditions using Ru(0) nanoparticles stabilized and controlled by the relevant choice of cavity and methylation degree of cyclodextrins.

Catalytically active nanoparticles stabilized by host-guest inclusion complexes in water.

Hydrogenation of arene derivatives can be successfully performed in water by using ruthenium(0) nanoparticles stabilized by 1 : 1 inclusion complexes formed between methylated cyclodextrins and an ammonium salt bearing a long alkyl chain.

N-Donor ligands based on bipyridine and ionic liquids: an efficient partnership to stabilize rhodium colloids. Focus on oxygen-containing compounds hydrogenation

Polynitrogen ligands and/in ionic liquids (ILs) are described as a pertinent tandem to efficiently stabilize rhodium nanoparticles (NPs) in the size range of 2.0 nm for catalytic applications. Several N-donor ligands based on bipyridine skeleton were used as extra protective agents in [BMI][PF(6)] and compared in the hydrogenation of functionalized aromatic compounds at 80 °C and under 40 bar H(2). The nature of the bipyridine derivative and its influence on the coordination mode on the particle surface were proposed to explain the observed different kinetic properties. The hydrogenation of various oxygen-containing arenes was investigated and original results were described in the reduction of anisole and cresols as model lignin compounds, providing a significant ratio of ketone derivatives. A first explanation based on possible reaction routes is proposed to justify the formed products.

Rhodium Colloidal Suspensions Stabilised by Poly‐N‐donor Ligands in Non‐Aqueous Ionic Liquids: Preliminary Investigation into the Catalytic Hydrogenation of Arenes

Ionic liquids (ILs), and more particularly imidazolium salts, have recently been used as templates for the preparation of stable noble-metal nanoparticles. These particles stabilised in ILs have proved to be efficient multiphase catalytic systems for various reactions, such as hydrogenation reactions. ILs are thus promising as they could play the dual role of solvent and protective agent. In that area, Dupont and co-workers have largely reported the synthesis of active metallic colloids in common ILs such as l-n-butyl-3-methylimidazolium hexafluorophosphate or tetrafluoroborate ([BMI] ACHTUNGTRENNUNG[PF6] or [BMI] ACHTUNGTRENNUNG[BF4]) in various catalytic reactions. However, in some cases, the aggregation of Rh or Ir nanoparticles has been observed during the catalytic hydrogenation of arene compounds. 2b] Consequently, the addition of a stabiliser could be required to avoid the agglomeration of rhodium nanospecies and to increase their stability in ILs. Different protective agents have already proved their efficiency, such as poly[(N-vinyl-2-pyrrolidone)-co-(1-vinyl3-alkylimidazolium halide)] copolymers, or poly(N-vinyl-2-pyrrolidone). This combination of ionic liquid and extra stabiliser has shown synergistic catalytic effects in terms of activity, selectivity and catalytic lifetime. Another approach relies on the use of ligands on the metal surface, such as phenanthrolineprotected palladium nanocatalysts for olefin hydrogenation in [BMI] ACHTUNGTRENNUNG[PF6] . More recently, our group reported the efficient stabilisation of zero-valent Rh nanoparticles in different nonaqueous ionic liquids with 2,2’-bipyridine (2,2’-Bipy) as an efficient N-donor ligand and their interesting activities and selectivities in arene hydrogenation reactions. We have also extended this study to bipyridine isomers (3,3’-Bipy and 4,4’Bipy) and showed the influence of the coordination mode of the ligand at the nanoparticle surface on the catalytic activity. Moreover, to avoid the formation of carbenes on the surface, we have also investigated the use of various salts such as methylbutylpyridinium or pyrrolidinium salts. 10] In fact, the presence of carbenes has recently been reported to justify that BMI can be potent poisons of nanocluster catalysts. In our case, no poisoning effect in terms of activity has been observed with the use of RhCl3·H2O as precursor of nanocatalysts in [BMI] ACHTUNGTRENNUNG[PF6] . On the basis of the efficient results obtained with Bipy ligands, we report herein the stabilisation by polynitrogen ligands with more complex structures, such as triazine and pyrazine derivatives and particularly 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ) and tetra-2-pyridinylpyrazine (TPPZ; Figure 1), and compare their catalytic activity and selectivity with those obtained for 2,2’-Bipy-protected systems.

Cyclodextrins as growth controlling agents for enhancing the catalytic activity of PVP-stabilized Ru(0) nanoparticles

Cyclodextrins act as growth controllers in the synthesis of PVP-stabilized Ru(0) nanoparticles, leading to enhancement of the catalytic activity in the hydrogenation of furfural.

Cyclodextrins as effective additives in AuNP-catalyzed reduction of nitrobenzene derivatives in a ball-mill

At the boundary between mechanochemistry, supramolecular chemistry and catalysis, the present study explores the role of cyclodextrins (CDs) and other saccharide additives in the mechanosynthesis of gold nanoparticles (AuNPs) and their use as catalysts in the reduction of substituted nitrobenzene derivatives into their corresponding aniline products. CDs not only allow for the stabilization of the AuNPs but also help diffuse a substrate within a solid mixture via supramolecular means, and orient the chemical reaction to the selective formation of aniline derivatives. Parameters influencing both the formation of AuNPs and the synthesis of aniline derivatives have been investigated. We show that the catalytic performance strongly depends upon the nature of the saccharide additive, the nature and location of the substituent on the benzene, and the ball-milling conditions. Water also plays a key role in both the reduction mechanism of the nitro groups and the supramolecular interactions with the substrate. Very interestingly, the amount of reductive agent (NaBH4) was drastically reduced compared to reductions performed in solution. Additionally, the catalytic system could be recycled over three consecutive runs without significant loss in activity, thus highlighting the efficacy of the combination of mechanochemistry, supramolecular chemistry, and catalysis.

Ruthenium-containing β-cyclodextrin polymer globules for the catalytic hydrogenation of biomass-derived furanic compounds

The confinement of catalytically active metallic nanoparticles within discrete and robust microenvironments was successfully achieved by using a water-compatible three-dimensional β-cyclodextrin-based polymer. The strategy was examined using ruthenium through an aqueous colloidal approach involving the chemical reduction of ruthenium nitrosyl nitrate by sodium borohydride in the presence of a water-soluble β-CD polymer crosslinked with citric acid (poly(CTR-β-CD)). The advantage of this polymer for nanoparticle synthesis is that (i) additional stabilizing effects are exerted through steric interactions (crosslinked chains and β-cyclodextrin entities) and electrostatic interactions (ionisable–COOH groups) and (ii) accessible nanopockets are provided between the stable junctions of the polymer skeleton. The poly(CTR-β-CD) Ru(0) system was characterized at different stages of the synthesis by combining proton nuclear magnetic resonance spectroscopy, dynamic light scattering and transmission electron microscopy measurements. The results highlighted that, in contrast with a series of control colloidal ruthenium catalysts, the specific use of poly(CTR-β-CD) allowed not only the stabilization of smaller size-controlled ruthenium nanoparticles (approximately 1.8 nm) but also their confinement in individual superstructures having sizes mostly in the range of 50 to 100 nm. These polymer-encapsulated ruthenium nanoparticles were applied as catalysts for the aqueous phase hydrogenation of biomass-derived 2-furaldehyde and 3-(2-furyl)acrolein under mild reaction conditions, i.e. 303 K and 1 MPa. The high reactivity was related to the presence of individual globular objects acting as catalytic “microreactors”, in which the consecutive hydrogenation reactions and product/substrate diffusional exchanges can occur efficiently in the confined spaces. The robustness of the system was demonstrated through recycling experiments and TEM characterizations after catalytic tests.

Evidence for the existence of crosslinked crystalline domains within cyclodextrin-based supramolecular hydrogels through sol–gel replication

The supramolecular hydrogel network formed from the association of poly(ethylene glycol) and α-cyclodextrin-based polypseudorotaxanes has been successfully replicated into a silica scaffold with a three-dimensional hierarchical pore structure by using a sol–gel process. The examination of the replicas indicates that the columnar polypseudorotaxane-based nanocrystallites act as crosslinkers maintaining the supramolecular hydrogel in a water-swollen state. Depending on the poly(ethylene glycol)/α-cyclodextrin formulation and the pH value, the resulting silica materials may exhibit a pore structure comprised of large mesopores (4–10 nm) interconnected by smaller ones (2–2.5 nm) in a framework where the pore walls are made-up of a microporous corona (<1.8 nm).

Carboxylated polymers functionalized by cyclodextrins for the stabilization of highly efficient rhodium(0) nanoparticles in aqueous phase catalytic hydrogenation

Rhodium(0) nanoparticles stabilized by a polymer containing carboxylate and β-cyclodextrin moieties have high stability and catalytic activity for aqueous hydrogenation reactions of olefins and aromatic substrates. This catalytic system can be recycled and reused without loss of activity. These high catalytic performances can be attributed to conjugated electrostatic interactions (carboxylate groups) and steric interactions (polymer structure and β-cyclodextrin moiety).

Noncovalent functionalization of multiwall carbon nanotubes by methylated-β-cyclodextrins modified by a triazole group

Multiwall carbon nanotubes have been efficiently suspended into water thanks to methylated β-cyclodextrins (CDs) containing a triazole group, itself substituted in the 4-position by hydrophilic moieties.