A strategy for the popularization of Si and C based nanochemistry – Si-POP
During this project, we will consider the synthesis of appropriate low-valent Si- and C-complexes with an enhanced thermal lability and the check of their potential as low-temperature-decomposable and clean precursors (single molecular source of atomic Si and C) of NPs. We also try to find efficient synthetic methods allowing to easily prepare various models of precursors. The large structural variation of available precursors would be helpful to check the relationship between their structure (+ electronic state) and decomposition pattern (quality of formed NP), which will provide an essential information to improve the models of precursors. We will also investigate the synthesis of small-sized Si(0)-clusters and their uses as seeds of Si-NPs. The self-assembly of these seeds or the resulting clusters (polymerization), which is well-controlled by the type of functional ligands, will provide an alternative way, in mild conditions, to access NPs in diverse formats such as size, crystallinity and porosity.
Deependra BAWARI has been recruited as post-doc on 15th May 2019. Having experience with the manipulation of highly reactive molecules, he has started his research with the reactivity study of known P,S-bis-ylide (R3P->C<-SPh2). Particularly, by substituting labile SPh2 ligand on the C(0) atom by a germylene, he successfully synthesized a new stable C(0) complex stabilized by a phosphine and a germylene ligands. We have also considered to use this C(0)-complex as a precursor of unprecedented mixed group-14 element source “CGe” (phosphine complex). However, although its reduction using potassium leads to the formation of amino-phosphine ligand, which indirectly indicates the generation of desired species, we could not detected it by NMR probably due to its unstable character.
S,S-bis-ylide (R2S->C<-SR2, carbon complex with two labile SPh2 ligands) is obviously one of the best models (C1 source) for our purpose. However, there are two major problems, which strongly limit its use: 1) the long synthetic pathway (9 steps), 2) its low stability (stable up to -30°C). Recently, we have developed a new straightforward synthetic route to the protonated precursor only in two steps from the same starting material (Ph2S). Using this simple method, we should be able to synthesize S,S-ylides with various different substituents just by using other sulfides (R2S) instead of Ph2S, which should allow us to find a more stable and thus easy-to-use models of S,S-ylides in near future.
We also found that Ph2SF2 reacts with a lithium trimethylsilylacetylide to produce a black carbon precipitate at room temperature. This is certainly due to the “in situ” generation of fragile Ph2S-CC species which readily decomposes to generate diatomic carbon “C2”. We currently look for better conditions to isolate (or detect) the Ph2S-CC species and also characterize the resulting carbon materials.
Toulouse team has successfully found simple ways to synthesize new C1-sources (S,S-bis-ylide 5) as well as a C2-reagent allowing to directly produce black carbon at room temperature. Therefore, we are now ready to investigate their potential as precursors of carbon based materials in solution.
Singapore team is capable of synthesizing novel silicon(0)-iron(0) and silicon(0)-cobalt clusters through a simple methodology using the NHC-silicon(I) iodide complex to undergo redox reactions with Fe2(CO)9 and Co2(CO)8. The clusters will be used as precursors to prepare Fe@Si and Co@Si nano materials for water splitting reactions.
It has been clearly demonstrated that the solution-based synthesis of nanoparticles (NPs) or nanocrystals (NCs) is a promising simple and benign method providing a number of advantages compared to the physical synthetic approaches. Indeed, in contrast to the physical methods generally effectuated using sophisticated and expensive equipment, the chemical method starting with the nucleation by thermal or chemical reduction of metallic precursors (simple chemical reactions in solution) do not require special apparatus and thus allows to synthesize various nanomaterials in ordinary chemical laboratories. The simplicity of chemical method has enormously contributed to popularize nanoscience (to make it accessible to most chemists).
"Is such a chemical-friendly-synthetic method of NPs also applicable to Group-14 element based nanomaterials?"
The answer is "no". In fact, although such non-metallic nanomaterials (semiconductor nanocrystals of silicon, nanotubes, graphenes,…) with a wide range of applications are exceedingly important, the major synthetic methods for them are still conventional physical or thin film methods and their solution-based synthesis remains much less common. This situation is certainly due to the lack of appropriate precursors able to generate the corresponding atomic elements in mild conditions (or triggering reactions). Indeed, there are only few reports on the synthesis of Si-NPs via the thermal decomposition of organosilicon compounds and, to the best of our knowledge, precursors allowing the low-temperature and solution-based synthesis of carbon-based NPs have not been described to date.
This project principally aims at developing the first appropriate (thermally labile) precursors allowing to synthesize various Si- and C-based nanomaterials in a normal flask using ordinary chemical synthetic techniques. The success of this project should provide to most of classical synthetic chemists an easy access to the research on Si- and C-nanomaterials, and thus should considerably accelerate their development.
Monsieur Tsuyoshi Kato (Centre National de Recherche Scientifique/Laboratoire héterochimie fondamentale et appliquée (LHFA))
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CNRS/LHFA Centre National de Recherche Scientifique/Laboratoire héterochimie fondamentale et appliquée (LHFA)
NTU Nanyang Technological University
NTU Nanyang Technological University
Help of the ANR 607,120 euros
Beginning and duration of the scientific project: December 2018 - 36 Months