Audrey Denicourt-Nowicki

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.

Rh(0) colloids supported on TiO2: a highly active and pertinent tandem in neat water for the hydrogenation of aromatics

TiO2-supported Rh(0) nanoparticles were easily prepared in one step without calcination by a room temperature impregnation of the inorganic support with a prestabilized colloidal Rh(0) suspension. They are highly active and reusable catalysts for the hydrogenation of aromatics and chloroanisole derivatives in neat water with TOFs up to 33000 h−1. The comparison with the analogous silica system Rh@SiO2 was discussed showing higher catalytic selectivities and activities with Rh(0) colloids supported on TiO2.

New ammonium surfactant-stabilized rhodium(0) colloidal suspensions: Influence of novel counter-anions on physico-chemical and catalytic properties

Novel anionic species, such as hydrogen carbonate (HCO(3)(−)), fluoride (F(−)), triflate (CF(3)SO(3)(−)), tetrafluoroborate (BF(4)(−)) and chloride (Cl(−)) were investigated as new partners of water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium salts, used as a protective agent of rhodium colloids. The effect of the surfactant polar head on the micellar behavior, size and morphology of the nanospecies was studied by adapted physico-chemical experiments (surface tension measurements, dynamic light scattering, thermogravimetric and TEM analyses) and discussed in terms of strong or weak stabilization of the growing nanoparticles surface. Finally, the influence of the nanoenvironment generated by the surfactant with various counter-anions was evaluated via the hydrogenation of aromatics.

TiO2-supported Rh nanoparticles: From green catalyst preparation to application in arene hydrogenation in neat water

TiO2-supported Rh(0) nanoparticles were prepared by an easy method under mild conditions in neat water. They proved to be highly active catalysts for arene hydrogenation in water with TOFs up to 33 333 h−1.

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.

A surfactant-assisted preparation of well dispersed rhodium nanoparticles within the mesopores of AlSBA-15: characterization and use in catalysis

Well dispersed and efficient Rh(0) hydrogenation catalysts were obtained by the reduction of Rh(III)-exchanged mesoporous aluminosilicates by sodium borohydride in the presence of N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium chloride.

Chiral ammonium-capped rhodium(0) nanocatalysts: synthesis, characterization, and advances in asymmetric hydrogenation in neat water.

Optically active amphiphilic compounds derived from N-methylephedrine, N-methylprolinol, or cinchona derivatives possessing bromide or chiral lactate counterions were efficiently used as protective agents for rhodium(0) nanoparticles. The full characterization of these surfactants and the obtained nanocatalysts was performed by means of different techniques. These spherical nanoparticles, with sizes between 0.8-2.5 nm depending on the stabilizer, were evaluated in the hydrogenation of model substrates in neat water as a green solvent. The rhodium catalysts showed relevant kinetic properties, but modest enantiomeric excess values of up to 13 % in the hydrogenation of ethyl pyruvate. They were also investigated in the hydrogenation of disubstituted arenes, such as m-methylanisole, providing interesting catalytic activities and a preferential cis selectivity of around 80 %; however, no asymmetric induction was observed.

Methylated β-Cyclodextrin-Capped Ruthenium Nanoparticles: Synthesis Strategies, Characterization, and Application in Hydrogenation Reactions

Colloidal suspensions of ruthenium nanoparticles (Ru0 NPs) stabilized by randomly methylated β‐cyclodextrins were easily prepared in aqueous solution by two comparative reductive approaches. The first method relies on a one‐step hydrogen reduction of ruthenium trichloride as a metal precursor in the presence of cyclodextrins (one‐pot method). The second method consists of the chemical reduction of metal salts by NaBH4, followed by the stabilization of ruthenium NPs by post‐addition of the methylated β‐cyclodextrins (cascade method). The modified β‐cyclodextrin‐capped ruthenium NPs obtained were characterized using TEM, DLS, and NMR techniques. The highly dispersed colloidal suspensions contain very small particles in the size range of 1–1.4 nm. Their catalytic performances were investigated in terms of activity and selectivity of their biphasic hydrogenation of various substrates (olefins, ketones, and disubstituted arenes) under mild conditions.

Efficient Ruthenium Nanocatalysts in Liquid–Liquid Biphasic Hydrogenation Catalysis: Towards a Supramolecular Control through a Sulfonated Diphosphine–Cyclodextrin Smart Combination

The combination between a sulfonated diphosphine (L) and a cyclodextrin (CD) allowed the preparation of very stable water‐soluble ruthenium nanoparticles (RuNPs) that displayed pertinent catalytic performances in hydrogenation of unsaturated substrates with a supramolecular control effect of the cyclodextrin. For comparison purpose, the RuNPs were produced by hydrogenation of the organometallic [Ru(1,5‐cyclooctadiene)(1,3,5‐cyclooctatriene)] complex under mild conditions (3 bar H2; room temperature) and in the presence of L or a L/CD mixture as stabilizer leading to Ru/L and Ru/L/CD systems, respectively. The so‐obtained nanoparticles were fully characterized by complementary techniques. Interestingly, NMR investigations evidenced 1) the strong coordination of the sulfonated diphosphine ligand at the metallic surface and 2) in the presence of cyclodextrin, the formation of an inclusion complex between L and CD that modified the coordination mode of the diphosphine. The investigation of both RuNPs systems in biphasic hydrogenation of unsaturated substrates pointed out relevant differences in terms of reactivity, thus evidencing the influence of the supramolecular interaction at the metallic surface on the catalytic performances of the nanocatalysts. This work took advantage of the supramolecular properties of a cyclodextrin to modulate the surface reactivity of diphosphine‐stabilized ruthenium nanoparticles and may open new opportunities in the field of nanocatalysis.