Frédéric Hapiot

The aminophosphine-phosphinites and related ligands: synthesis, coordination chemistry and enantioselective catalysis

Abstract The synthesis and coordination chemistry of aminophosphine-phosphinites (AMPP) and closely related ligands is reviewed. Asymmetric catalytic reactions involving organometallic-AMPP complexes are presented. Examples of enantioselective C–C bond formation in the presence of nickel- (dienes and diene-olefins dimerization, allylic substitution) and palladium-AMPP catalysts (nucleophilic addition to allylic substrates), hydroformylation based on platinum and rhodium complexes, rhodium-based hydrosilylation, hydrogenation of CC and CO bonds in the presence of rhodium and ruthenium complexes and homo Diels-Alder catalyzed by cobalt species are presented.

Recent breakthroughs in aqueous cyclodextrin-assisted supramolecular catalysis

During the past twenty years, cyclodextrins (CDs) have proven to be very effective in aqueous biphasic catalysis. They could act as molecular receptors for numerous organic substrates and favour their conversion at the aqueous/organic interface. Recently, new applications have been found for CDs in aqueous catalysis. CDs can now be defined as polyfunctional entities between the substrate-containing phase and the catalyst-containing phase. In this paper, we highlight the latest breakthroughs in the use of CDs in catalysis through several examples from the literature.

Cyclodextrins as Mass Transfer Additives in Aqueous Organometallic Catalysis

During the past fifteen years, the use of chemically modified cyclodextrins (CDs) in aqueous organometallic catalysis has sig- nificantly contributed to enlarge the application field of biphasic processes in chemistry. In this paper, we describe how these su- pramolecular receptors became one of the most efficient solutions to solve mass transfer problems in aqueous organometallic catalysis. The scientific gaps that have been cleared to explain the exact role of the CDs in these biphasic systems are especially emphasized. In particular, the impact of supramolecular interactions between chemically modified CDs and substrates, water soluble ligands or or- ganometallic catalysts is addressed for a better understanding of the recognition processes involved in the catalytic reactions.

Unusual Inversion Phenomenon of β-Cyclodextrin Dimers in Water

A conformational analysis of three triazole-containing bridged bis-β- cyclodextrins (CD) has been carried out to evaluate their recognition ability. NMR spectroscopy and ITC measurements clearly demonstrate that one of the CD glucopyranose units undergoes a 360° rotation in water so that the spacer linking the two CDs is deeply included into one of the CD cavities. The amplitude of this inversion phenomenon depends on the nature of the spacer and results in a limited accessibility to the CD cavities in line with previous catalytic results.

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.

Impact of cyclodextrins on the behavior of amphiphilic ligands in aqueous organometallic catalysis.

Summary In this study, we showed that the addition of randomly modified β-cyclodextrin (RAME-β-CD) in aqueous medium could have a beneficial impact on the catalytic performances of phosphane-based aggregates in the Pd-catalyzed cleavage of allyl carbonates (Tsuji–Trost reaction). The RAME-β-CD/phosphane supramolecular interactions helped explain the catalytic results. The presence of RAME-β-CD in the aqueous compartment improved the phosphane-based aggregate dynamics. The exchanges between the hydrophobic substrate-containing aggregate core and the catalyst-containing aqueous phase were then greatly favored, resulting in an increase in the catalytic performances.

Supramolecularly controlled surface activity of an amphiphilic ligand. Application to aqueous biphasic hydroformylation of higher olefins

A biphasic catalytic system has been elaborated in which the amphiphilic species concentrations at the aqueous/organic interface could be thermocontrolled by the supramolecular interaction between β-cyclodextrins and the 1-(4-tert-butyl)benzyl-1-azonia-3,5-diaza-7-phosphaadamantyl ligand (1). The system proved efficient in Rh-catalyzed hydroformylations of higher olefins. An increase in the catalytic activity was observed without alteration in either the chemo- or the regio-selectivity. The main advantage of the cyclodextrin/1 couple lies in the rapid decantation of the biphasic system at the end of the reaction. This study represents the first example of thermoregulation of the surface activity of an amphiphilic phosphane by a cyclodextrin.

Catalytic Decarbonylation of Biosourced Substrates

Linear α-olefins (LAO) are one of the main targets in the field of surfactants, lubricants, and polymers. With the depletion of petroleum resources, the production of LAO from renewable feedstocks has gained increasing interest in recent years. In the present study, we demonstrated that Ir catalysts were suitable to decarbonylate a wide range of biosourced substrates under rather mild conditions (160 °C, 5 h reaction time) in the presence of potassium iodide and acetic anhydride. The resulting LAO were obtained with good conversion and selectivity provided that the purity of the substrate, the nature of the ligand, and the amounts of the additives were controlled accurately. The catalytic system could be recovered efficiently by using a Kugelrohr distillation apparatus and recycled.

Using click chemistry to access mono- and ditopic β-cyclodextrin hosts substituted by chiral amino acids.

A wide range of chiral mono- and ditopic cyclodextrin-based receptors have been synthesized by CuI-catalyzed azide-alkyne cycloaddition starting from mono-6-azido-β-cyclodextrin and chiral amino acids. Of interest, microwaves proved very efficient to access a wide range of ditopic β-cyclodextrin receptors with quantitative yields.

A Property-Matched Water-Soluble Analogue of the Benchmark Ligand PPh3

A series of sulfonated biphenylphosphanes were readily prepared from commercially available, inexpensive, and air-stable organic compounds. Of these, the trisulfonated trisbiphenylphosphane can be considered as a true water-soluble analogue of PPh(3) as the cone angle and basicity of both phosphanes are very close and result in a similar coordination mode on palladium and rhodium complexes. The catalytic performance of the trisulfonated trisbiphenylphosphane was evaluated in the aqueous hydroformylation of 1-decene and the Tsuji-Trost reaction.