Nanogels for MultiCatalytic Domino Reactions

Project description and results

The aim of the project was to support and stabilize catalytically active metallic species in the inside of nanometric swellable polymer structures, notably in nanogels. This special type of polymeric catalytic support should give rise to quasi-homogeneous catalysis and should combine the advantages of both homogeneous and heterogeneous catalysis: whereas the homogeneous character of the catalysis is preserved, the catalytic species (and possibly temporarily the reacting intermediates) are immobilized and sequestered in the polymer matrix (through physical or chemical entrapping), which should make recycling of the catalytic system possible. Our idea was to use our formerly developed core-shell structured nanogels (NG) possessing a stabilizing shell and a swellable core as supports for Pd(0) nanoparticles. For the coordination of Pd, dimethylaminoethylacrylate (DMAEA) was incorporated as a comonomer in the NG core.

A simple and mild process using ethanol as reductive agent was used to produce Pd(0) NP from a Pd(II) salt in the core of the nanogels. Very small Pd particles were formed with an average diameter of Dn = 3 nm, no bigger NP or aggregates were observed.

The potential of this novel catalyst system, called PdNP@NG, was evaluated in the C-C Mizoroki-Heck coupling between 4-bromo-acetophenone and n-butylacrylate used as a benchmark reaction .It appeared that the complex structure of the core-shell NG did not affect the catalytic performance of the palladium NP compared to non-supported catalytic systems. In addition, a substrate screening was performed with various activated bromo-arenes and iodo-arenes, corroborating the good catalytic activity, with only 0.1 mol% Pd. The hybrid NG could be isolated as a solid powder, and the Pd(0) NP, embedded in the nanogel’s core, showed remarkable stability with preserved activity for long periods of time - both in the solid and in solution, i.e. even in the presence of air and moisture. Furthermore, the catalyst could be isolated by precipitation, stored, and recycled up to three times without significant activity loss. After three cycles however, the catalyst lost most of its activity, which was attributed to palladium leaching out of the NG into the organic solution. Palladium leaching seems to occur during the catalysis, probably after the oxidative addition step, which is expected to take place in the core of the NG.

Summary

In summary, a Pd(0)NP containing nanogel was developed which displays a remarkable stability in both solid state and in solution. This feature allowed its successful application as catalyst for the Mizoroki-Heck reaction between n-butyl acrylate and a series of bromo- and iodo-arenes. The yields spanned from good to excellent, and catalyst recycling could be achieved up to three times without significant activity loss. Furthermore, three-phase tests not discussed above indicated that the hybrid nanogel acts as a Pd(0) nano-reservoir. The catalysis proceeds in a quasi-homogenous fashion, with part of the catalytic activity occurring outside the nanogel explaining the observed limited recyclability. In parallel, in the internship of Fanny Do in 2015, a Hoveyda-Grubbs Ruthenium catalyst has been successfully coordinated to poly(N,N-dimethylacrylamide) chains into which specific coordinating monomer units had been incorporated. In the framework of this Master, our preliminary results showed that this polymer-supported catalyst was active in ring-closing metathesis and a first recycling test could successfully be performed.

publication

• André Pontes da Costa, Danilo Rosa Nunes, Mickaël Tharaud, Julie Oble, Giovanni Poli et al. 
  Pd(0)-Nanoparticles Embedded in Core-Shell Nanogels as Recoverable Catalysts for the Mizoroki-Heck
  Reaction ChemCatChem, Wiley, 2017, 9 (12), pp.2167-2175
  DOI : 10.1002/cctc.201601645?
  Ref HAL : hal-01495948v1

Interventions en séminaire, congrès

1. From nanogels & nanoparticles towards functional materials via PISA. J. Rieger Séminaire au IS2M. “Mulhouse, France, dec 2017.
2. De nanogels et nanoparticules aux matériaux fonctionnels par PISA Club Emulsion 2017, Lyon, France, oct 2017. (INVITED Presentation)
3. From Core-Shell Nanogel Catalysis to Green Applications of the Murai Reaction G. Poli 4th International Workshop on Pericyclic Reactions and Synthesis of Hetero- and Cabocyclic Systems, Italy, juin 2017. (INVITED Presentation)
4. Pd-containing Core-Shell Nanogels: Application to the Mizoroki-Heck Reaction A. P. da Costa, D. R. Nunes, J. Oble, G. Poli, J. Rieger in 5th CARISMA Meeting - Catalytic Routines for Small Molecule Activation, Lisbon, Portugal, March 2017. Oral communication 
5. Hybrid Core-Shell Nanogels: Recyclable Nanoreactors for Catalysis A. P. da Costa, D. R. Nunes, J. Oble, G. Poli, J. Rieger in 7ème Journée du Groupe Français des Polymères – Ile de France, Thiais, France, Sept 2016. Oral communication
6. Hybrid Core-Shell Nanogels as Catalytic Nanoreactors A. P. da Costa, F. Stoffelbach, J. Oble, G. Poli, J. Rieger in FCCat – French Conference on Catalysis, Frejus, France, Mai 2016. Oral communication
7. Polymer Nanogels as Recyclable Matrix for Catalysis (NACRE) A. P. da Costa, F. Stoffelbach, J. Oble, G. Poli, J. Rieger in Journée Thématique Chimie et Environnement, Paris, France, janv 2016. Oral communication
8. Nanogels for Multicatalytic Domino Reactions A. P. da Costa, F. Do, J. Oble, F. Stoffelbach, G. Poli and J. Rieger in Journées Scientifiques Labex Michem, Paris, France, June 2015. Poster.
9. Core-Shell Nanogels for Catalysis   A. P. da Costa, F. Do, J. Oble, F. Stoffelbach, G. Poli and J. Rieger in P2M : Precision Polymer Materials, Lacanau, France, Mai 2015. Poster.