Christian Pradel

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.

Copper(I) Oxide Nanoparticles in Glycerol: A Convenient Catalyst for Cross‐Coupling and Azide–Alkyne Cycloaddition Processes

Well‐defined and small copper(I) oxide nanoparticles stabilised by poly(vinylpyrrolidone) in neat glycerol have been synthesised under a dihydrogen atmosphere. The as‐prepared material has been successfully applied in Cheteroatom couplings and azide–alkyne cycloadditions to give the desired products selectively with isolated yields higher than 90 %. Different amines have been used in the CN couplings, which include aqueous ammonia, that led to the synthesis of anilines. Mono‐1,4‐disubstituted triazoles and also bis‐ and tris(triazoles) have been obtained by the regioselective Cu‐catalysed Huisgen reaction, which comprises the synthesis of dissymmetrical substituted bis(triazoles). The catalytic glycerol phase could be recycled at least ten times and keeps its activity and selectivity. Moreover this versatile catalyst allowed tandem cycloaddition/CN coupling processes to give the corresponding polyfunctional products in a high global yield without the isolation of intermediates.

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.

Palladium nanoparticles stabilised by cinchona-based alkaloids in glycerol: efficient catalysts for surface assisted processes

Palladium nanoparticles (PdNPs) were synthesised and fully characterised, both in solution and the solid state, using naturally-occurring cinchona-based alkaloids in neat glycerol. These nano-systems were stable under reaction conditions, finding applications in hydrogenation and hydrodehalogenation processes, as a result of their surface-like behaviour. Their reactivity was improved in relation to that involving PdNPs stabilised by phosphines and also by Pd/C as a heterogenous catalyst, mainly in terms of recyclability. In particular, the colloidal palladium catalyst stabilised by quinidine was highly efficient to promote the hydrodechlorination of aromatic compounds under low dihydrogen pressure. These original catalysts found applications in the synthesis of secondary and tertiary amines including N-substituted anilines, by means of one-pot tandem Pd-catalysed methodologies under smooth conditions. In all of these processes, glycerol performed a crucial function as a liquid support for the immobilisation of nanoparticle-based catalysts, allowing both the stabilisation of the nano-catalysts and easy recycling of the catalytic phase.

Key non-metal ingredients for Cu-catalyzed 'Click' reactions in glycerol: nanoparticles as efficient forwarders

The effect of long-alkyl-chain amines in CuI-assisted azide-alkyne cycloadditions of terminal alkynes with organic azides in glycerol and other environmentally benign solvents (water, ethanol) has been examined. The presence of these additives favors the in situ formation of CuI -based nanoparticles and results in an increase of the catalytic reactivity. In glycerol, liquid-phase transmission electron microscopy (TEM) analyses, enabled by the negligible vapor pressure of this solvent, proved that CuI nanoparticles are responsible for the observed catalytic activity. The wide variety of alkynes and azides of which this effect has been investigated (14 combinations) confirms the role played by these additives in Cu-catalyzed Huisgen cycloadditions.