Self-assembling of gold nanoparticles directed by fullerenes-based nodes for heterogeneous catalysis – FULOR

The proposal focuses on the advancement of a synthetic approach of molecular control of structure, shape, and functionality by means of rationally designing modular ligands and atomically precise clusters in order to get a high size ratio between them. To direct the assembly of nanoparticles and prevent their aggregation, the aim is to use functionalized hexa-adduct fullerenes as 3D rigid and defined nodes. In addition, to keep control at the molecular level of the self-assembly, atomically well-defined thiolate gold nanoclusters with Aun(SR)m formula will be used. The advantages of these sub-2 nm gold clusters is that the number n of gold atoms and m of thiolate ligands are known and numerous clusters with stable (n,m) composition from (10,10) up to (333,79) have been isolated. To self-assemble the gold clusters through organic linkers, two generations of functionalized hexa-adduct fullerene systems have been designed with diameters ranging from 3 to 7 nm. The first system is functionalized hexa-adduct fullerenes with twelve sulfur-based terminal functions. To couple by strong covalent or weak electrostatic bonds those organic species with gold nanoparticles direct synthesis from chloroauric acid or exchange / insertion reactions from Aun(SC2H4Ph)m will be carried out. The second generation of hexa-adduct fullerenes are made of allyl or carboxylate terminal functions for click or peptidic coupling with Aun(SR-X)m gold nanoclusters with X = azide or amino groups, respectively. Finally, the new porous materials will be tested for aerobic oxidation of alkenes or alcohols or carbon-carbon coupling catalytic reactions. This interdisciplinary project represents a new strategy towards the design of innovative catalysts and will be an opportunity to develop both novel functional and nanostructured hybrid materials as well as improvements in catalysis that will find widespread applications in materials chemistry.

We synthesized a new fullerene hexaakis adduct incorporating twelve thiocyanate functions on its surface. Coupling this 3D organic linker and thiocyanate external functions with a one-pot synthesis involving LiBH4 as a reducing agent results in the in situ formation of sub-3 nm AuNPs and their assembly into a 3D-network. Different techniques used for in-depth characterizations of the materials reveal that the AuNP size is homogeneous, they are connected through strong Au–S bonds and the interparticular space is occupied by only one layer of C60 moieties.

The association of ultra-small AuNPs with a carbon-based organic linker in one network makes this kind of hybrid material promising as a catalyst with potential synergistic effects between the two parts. By selecting well designed organic linkers with the appropriate external functions and well-adapted synthesis, the formation of robust and organized 3D-networks of small nanoparticles should be soon possible.

G. Rousseau, C. Lavenn, L. Cardenas, S. Loridant, Y. Wang, U. Hahn, J.-F. Nierengarten, A. Demessence*, Chem. Commun., 2015, 51, 6730-6733. One-pot synthesis of sub-3 nm gold nanoparticle networks connected by thio-based multidentate fullerene adducts.

Development of new catalysts to improve industrially important chemical reactions in terms of activity and selectivity, in environmentally more acceptable means and economical matter is one of the most important needs in research. Heterogeneous catalysis has shown its potential over the last years with the discovery of new catalysts easy to separate from the reaction medium. Today, nanoparticles, and particularly gold clusters, are considered as the most exciting materials in heterogeneous catalysis due to their high surface / volume ratio allowing for a high numbers of catalytically active sites. Nevertheless, the main problem associated with the use of nanoparticles-based catalysts is their dispersion. When particles form stable colloidal solution, they show good activity and dispersion, but once exhausted, they are difficult to regenerate. In contrast, when nanoparticles are immobilized on a support they are easier to regenerate and still remain in a dispersed state, but these composites exhibit a lower accessible surface area, due to the support, that thus limits their inherent effectivity and in general the support effect is not negligible. To overcome these limitations, this proposal aims to develop new nanostructured materials by using the concepts of self-assembly and self-organization of nanoparticles directed by organic linkers to generate multifunctional hybrid materials. More precisely, the goal is to organize atomically well-defined nanoparticles into a 3D-network with specified arrangement to create porosity and a highly dense surface area availability of the catalytically active units. The creation of a 3D porous network would reveal a new nanoscale pathway and catalytic phenomena in the liquid or gas media, with good mass transfer of species and good selectivity depending on the pores geometry. The proposal focuses on the advancement of a synthetic approach of molecular control of structure, shape, and functionality by means of rationally designing modular ligands and atomically precise clusters in order to get a high size ratio between them. To direct the assembly of nanoparticles and prevent their aggregation, the aim is to use functionalized hexa-adduct fullerenes as 3D rigid and defined nodes. In addition, to keep control at the molecular level of the self-assembly, atomically well-defined thiolate gold nanoclusters with Aun(SR)m formula will be used. The advantages of these sub-2 nm gold clusters is that the number n of gold atoms and m of thiolate ligands are known and numerous clusters with stable (n,m) composition from (10,10) up to (333,79) have been isolated. To self-assemble the gold clusters through organic linkers, three generations of functionalized hexa-adduct fullerene systems have been designed with diameters ranging from 3 to 7 nm. The first system is functionalized hexa-adduct fullerenes with twelve sulfur-based terminal functions. The second generation is constituted of up to 96 dendritic ammonium terminal functions to provide to the system a certain flexibility and serendipity to generate thermodynamically favorable structures. To couple by strong covalent or weak electrostatic bonds those organic species with gold nanoparticles direct synthesis from chloroauric acid or exchange / insertion reactions from Aun(SC2H4Ph)m will be carried out. Finally the third generation of hexa-adduct fullerenes are made of six allyl or carboxylate terminal functions for click or peptidic coupling with Aun(SR-X)m gold nanoclusters with X = azide or amino groups, respectively. Finally, the new porous materials will be tested for aerobic oxidation of alkenes or alcohols or carbon-carbon coupling catalytic reactions. This interdisciplinary project represents a new strategy towards the design of innovative catalysts and will be an opportunity to develop both novel functional and nanostructured hybrid materials as well as improvements in catalysis that will find widespread applications in materials chemistry.