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Catalysis and
Supramolecular Chemistry

Nanomaterials
and photonics

 


CATALYSIS AND SUPRAMOLECULAR CHEMISTRY

 

SUPRAMOLECULAR SELF-ASSEMBLY FOR CATALYSIS

(Person in charge: Pr. Frédéric Hapiot)

 

1- Inversion phenomenon in CD-dimers

For decades the idea that CDs are rigid structures has fueled research into their molecular recognition properties. However, structural alteration of CDs is not inconsequential. For example, we showed that CD dimers undergoes a 360° rotation in water so that the spacer linking the two CDs is deeply included into one of the CD cavities. The magnitude of this inversion phenomenon depends on the nature of the spacer and results in a limited accessibility to the CD cavities. It was shown that the inversion phenomenon occurring in CD-dimers greatly affects their catalytic properties in aqueous biphasic catalysis. This underestimated effect is also the cause of numerous mistakes throughout the scientific literature about CDs.

Fig. 1

References:

  1. «Limits of the Inversion Phenomenon in Triazolyl-Substituted β-Cyclodextrin Dimers»
    J. Potier, S. Menuel, N. Azaroual, E. Monflier, F. Hapiot
    Eur. J. Org. Chem. 2014 -1547-1556
    - doi: 10.1002/ejoc.201301681

  2. «Unusual Inversion Phenomenon of β-Cyclodextrin Dimers in Water»
    S. Menuel, N. Azaroual, D. Landy, N. Six, F. Hapiot, E. Monflier
    Chem. Eur. J., 2011, 3949-3955
    - doi: 10.1002/chem.201003221

2- Supramolecular bidentate ligands

Water-soluble self-assembled ligands have been elaborated through hydrophobic effects using appropriate CD/phosphane combinations. The resulting supramolecular PN and PNN ligands are capable of coordinating platinum, palladium and rhodium complexes, with the CD simultaneously acting both as a first- and second-sphere ligand. Such supramolecular ligands find application in hydrogenation and hydroformylation of alkenes, Heck arylation, and a domino reaction where a Pt-catalyzed reduction of nitrobenzene is followed by a Paal–Knorr pyrrole reaction.

Fig. 2

References:

  1. «Functionalized Cyclodextrins as First and Second Coordination Sphere Ligands for Aqueous Organometallic Catalysis»
    F. Hapiot, H. Bricout, S. Tilloy, E. Monflier
    Eur. J. Inorg. Chem. 2012, 1571–1578
    - doi: 10.1002/ejic.201101316

  2. «Multifunctional cyclodextrin-based N,N-bidentate ligands for aqueous Heck arylation»
    J.Potier, S.Menuel, J.Rousseau, S.Tumkevicius, F.Hapiot, E.Monflier
    Applied Catalysis A:General, 2014, 479, 1-8
    - doi: 10.1016/j.apcata.2014.04.021

  3. «Cyclodextrin-based PNN supramolecular assemblies: a new class of pincer-type ligands for aqueous organometallic catalysis»
    S. Menuel, E. Bertaut, E. Monflier, F. Hapiot
    Dalton Trans. 2015, 44, 13504–13512
    - doi: 10.1039/C5DT01825K

3- CD-grafted polymers

CD-grafted polymers functionalized with water-soluble phosphanes were synthesized starting from poly(N-acryloyloxysuccinimide) (polyNAS). They were used as additives in Rh-catalyzed hydroformylation of terminal alkenes. When the catalyst-stabilizing phosphane was not grafted to the polymer chain, a structure−activity investigation provided compelling evidence that positive cooperativity is operative in this catalytic system. Indeed, two close-in-space CDs contribute to improve the recognition process of long alkyl chain alkenes by multivalency. When the phosphane was grafted onto the polymer chain, both the supramolecular properties of the CD and the coordination ability of the phosphane were combined into the same molecular object. During the course of the reaction, the closeness of the three main protagonists (substrate, CD, phosphane) leads to a significant increase in the conversion compared to a catalytic system where the CD and the phosphane are not grafted on the same polymer chain.

Fig. 3

References:

  1. «Cyclodextrin-grafted polymers functionalized with phosphanes: a new tool for aqueous organometallic catalysis»
    J. Potier, S. Menuel, D. Mathiron, V. Bonnet, F. Hapiot, E. Monflier
    Beilstein J. Org. Chem. 2014, 10, 2642-2648
    -.doi: 10.3762/bjoc.10.276

  2. «Cooperativity in Aqueous Organometallic Catalysis: Contribution of Cyclodextrin-Substituted Polymers»
    J. Potier, S. Menuel, D. Fournier, S. Fourmentin, P. Woisel, E. Monflier, F. Hapiot
    ACS Catalysis, 2012, 2, 1417-1420
    - doi: 10.1021/cs300254t

Poly(N-isopropylacrylamide) (PolyNIPAM) chain end-decorated by a randomly methylated β-CD (RAME-β-CD) are also effective to favor aqueous biphasic hydroformylation of alkenes using water soluble Rh-catalyst. Above the lower critical solution temperature (LCST), the CD-grafted polyNIPAM self-assemble into aggregates of micrometer size range. These aggregates adsorb at the organic/aqueous interface to form a Pickering emulsion which proved to favor molecular contacts between the substrate and the catalyst.

Fig. 4

Reference:

  1. «Thermoresponsive self-assembled cyclodextrin-end-decorated PNIPAM for aqueous catalysis»
    J. Potier, S. Menuel, J. Lyskawa, D.Fournier, F. Stoffelbach, E. Monflier, P. Woisel, F. Hapiot
    Chem. Commun., 2015, 51, 2328-2330
    - doi: 10.1039/c4cc09052g

4- Supramolecular hydrogels

Supramolecular hydrogels are soft-materials generated by the entrapment of large quantities of water within a superstructure made of non-reticulated fibrils of varying dimensions. They exhibit reversible sol–gel transition upon exposure to external stimuli such as temperature. Such physico-chemical property has been exploited in transition metal catalysis, especially to recover and recycle the organometallic catalyst. Pickering-like emulsions are operative in these biphasic systems and promote molecular contacts between hydrophobic substrates and water soluble catalysts, especially in hydroformylation of long chain alkenes.

Fig. 5

References:

  1. «Pickering Emulsions Based on Supramolecular Hydrogels: Application to Higher Olefins’ Hydroformylation»
    J. Potier, S. Menuel, M.-H. Chambrier, L. Burylo, J.-F. Blach, P. Woisel, E. Monflier, F. Hapiot
    ACS Catalysis 2013 , 3, pp 1618–1621
    - doi: 10.1021/cs4002282

  2. «Synergetic effect of randomly methylated ß-cyclodextrin and supramolecular hydrogel in Rh-catalyzed hydroformylation of higher olefins»
    J. Potier, S. Menuel, E. Monflier, F. Hapiot
    ACS Catalysis 2014, 4, 2342-2346
    - doi: 10.1021/cs5004883

  3. «Tetronics/cyclodextrin-based hydrogels as catalyst-containing media for the hydroformylation of higher olefins»
    M. Chevry, T. Vanbesien, S. Menuel, E. Monflier, F Hapiot
    Catal. Sci. Technol., 2016, in press
    - doi: 10.1039/C6CY02070D

5- Supramolecular Emulsifiers in Biphasic Catalysis

Hydroformylated triglycerides are of interest because they find application in the synthesis of plasticizers, polymers, and lubricants. We found that the C=C double bonds of triglycerides can be readily converted into aldehydes using an aqueous biphasic system for which an organometallic Rh complex is retained within the aqueous compartment. The triglycerides drive their own conversion because of the transient formation of surface active CD/triglyceride supramolecular complexes during the course of the reaction. Upon stirring, the CD/triglyceride supramolecular complex acts as a self-emulsifier that significantly increases the surface area between the triglyceride organic phase and the catalyst-containing aqueous phase. Because hydroformylated triglycerides do not interact with CDs, the product and the catalyst can be recovered separately by simple decantation once the reaction is complete.

Fig. 6

References:

  1. «A self-emulsifying catalytic system for the aqueous biphasic hydroformylation of triglycerides»
    T. Vanbésien, A. Sayede, E. Monflier, F. Hapiot
    Cat Sci Technol 2016, 6, 3064 - 3073
    - doi: 10.1039/C5CY01758K

  2. «Supramolecular emulsifiers in biphasic catalysis: the substrate drives its own transformation»
    T. Vanbésien, F. Hapiot, E. Monflier
    ACS Catal. 2015, , 5, 4288-4292
    - doi: 10.1021/acscatal.5b00861

6- Synthesis and catalysis under mechanochemical conditions

Through hydrophobic effects at the solid state, α-, β-, and γ-CDs were modified on their challenging secondary face by mechanosynthesis at room temperature using a laboratory scale ball-mill. Mono-(2,3-manno-epoxide) α-, β-, and γ-CDs were subsequently synthesized by ball-milling a mixture of monotosylated α-, β-, and γ-CDs, respectively, and KOH.

Fig. 7

Mechanochemistry also proves effective for Greener Paal-Knorr pyrrole synthesis. Relative to traditional Paal–Knorr methodologies, various N-substituted pyrroles were obtained in very short reaction times. By reaction with unreactive diketones, desymmetrized aliphatic and aromatic compounds were also synthesized.

Fig. 8

We also explore the role of 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. 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.

Fig. 9

References:

  1. «Selective secondary face modification of cyclodextrins by mechanosynthesis»
    S. Menuel, B. Doumert,; S. Saitzek, A. Ponchel, L. Delevoye, E. Monflier, F. Hapiot
    J. Org. Chem. 2015, 80, 6259-6266
    - doi: 10.1021/acs.joc.5b00697

  2. «Greener Paal-Knorr pyrrole synthesis by mechanical activation»
    L. Akelis, J. Rousseau, R. Juskenas, J. Dodonova, C. Rousseau, S. Menuel, D. Prevost, S. Tumkevičius, E. Monflier, F. Hapiot
    Eur. J. Org. Chem. 2016, 31-35
    - doi: 10.1002/ejoc.201501223

  3. «Cyclodextrins as Effective Additives in AuNPs-Catalyzed Reduction of Nitrobenzene Derivatives in a Ball-Mill»
    S. Menuel, B. Léger, A. Addad, E. Monflier, F. Hapiot
    Green Chem. 2016, 18, 5500–5509
    - doi: 10.1039/C6GC00770H
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