ED Sciences Chimiques
Metallacarborane-based silica nanohelices: Innovative chiral nanocatalysts for asymmetric transformation in water
by Hao WANG (Institut de Chimie & de Biologie des Membranes & des Nano-objets)
The defense will take place at 14h00 - IECB Amphitheatre 2 Rue Robert Escarpit, 33600 Pessac
in front of the jury composed of
- Sylvain NLATE - Maître de conférences - Université de Bordeaux - Directeur de these
- Reiko ODA - Directrice de recherche - CNRS - CoDirecteur de these
- Stéphane BELLEMIN-LAPONNAZ - Directeur de recherche - CNRS - Rapporteur
- Riina AAV - Full professor - Tallinn University - Rapporteur
- Brigitte BIBAL - Professeure - Université de Bordeaux - Examinateur
- Emmanuel CADOT - Professeur des universités - Université de Versailles Saint-Quentin-en-Yvelines - Examinateur
Chiral materials have attracted particular interest in recent years due to their remarkable properties and potential applications, particularly in the field of asymmetric catalysis. The objective of this thesis is to prepare, characterize and study the chiroptical properties of a series of enantiopure helical nanostructures based on cobaltabis(dicarbollide) (COSAN) and polyoxometalate (POM). The effectiveness of these nanomaterials as heterogeneous photocatalysts in the enantioselective oxidation of alcohols will then be evaluated. Firstly, left-handed and right-handed enantiopure silica hybrid nanohelices based on COSAN were prepared and characterized. In these helical structures, achiral COSAN anions are encapsulated into organic-inorganic hybrid nanohelices, which serve as a chiral platform to induce chirality in COSAN for enantioselective transformations. The morphology and structural composition of these hybrids, as well as the presence of COSAN anions were confirmed by UV/Vis, Raman, TEM, NMR and EELS. Their optical activity was demonstrated by CD and ROA, highlighting the chirality induction of chiral hybrid nanohelices to achiral COSAN anions. Furthermore, these hybrids exhibit excellent catalytic activity and enantioselectivity in the photooxidation of aromatic secondary alcohols in water, reaching up to 85% enantiomeric excess. Remarkably, these catalysts were recovered and reused at least three times without loss of catalytic activity or enantioselectivity. We then focused on the chirality induction of silica nanohelices on POMs. Thus, a series of right-handed and left-handed hybrid silica nanohelices based on the trianionic Keggin POM [α-PW12O40]3− was prepared by anion exchange. They were characterized by TEM, EDX, UV/Vis, CD and ROA, confirming their helical structure and their optical activity. These POM-based hybrid silica nanohelices are efficient catalysts in the photooxidation of aromatic secondary alcohols, with an enantioselectivity of up to 56%. They are stable, recoverable and reusable for at least three cycles without loss of catalytic activity or enantioselectivity.