Triptycenes and helicenes as polyaromatic platform for the design of bulky phosphines, boranes and bifunctional catalysts.

Abstract

Ambiphilic compounds possessing two antagonistic chemical functions, such as a Lewis acidic and a Lewis basic site, are increasingly used as bifunctional catalysts,
chemosensors and ligands. Lewis acids and bases are usually incompatible chemical species since they combine to form a Lewis adduct, which annihilates their respective acidic and basic properties.
According to the concept of Lewis acid and base introduced in 1923 by Gilbert N. Lewis: “The basic substance furnishes a pair of electrons for a chemical bond, the acid substance accepts such a pair”. By sharing the electron pair, a Lewis adduct containing a covalent bond between the acid and the base is formed, bearing in mind that this process can be reversible depending on the acidity and basicity strength of both species.
Numerous strategies can be employed to control this association process, notably by modulating the steric and electronic properties of the substituents attached to the acidic and basic atoms. Indeed, with large substituents, the steric hindrance prevents the antagonistic functions to react and quench each other’s because of steric repulsions, and result in a so called “Frustrated Lewis Pairs” (or FLPs).
It is thus possible to design new catalysts containing a Lewis acid and a Lewis base and which coexist simultaneously in solution without any covalent interactions between these two reactive sites and without dimerization of the catalysts.
With this in mind, our main goal was to synthesize and investigate the reactivity of new bifunctional phosphine-borane compounds featuring two types of linker never used previously: triptycene and helicene scaffolds.
The first chapter of this dissertation is a detailed presentation of frustrated Lewis pairs and their applications and reactivities towards small molecules. In a second chapter, the synthesis of new hindered boranes and phosphines based on the triptycene scaffold and their reactivity as frustrated Lewis pairs are presented. Finally, in the third chapter, the synthesis and study of bulky phosphines based on hetero[5]helicene scaffolds are discussed.

Date of Award	29 Sept 2022
Original language	English
Awarding Institution	University of Namur
Sponsors	FSR-FNRS
Supervisor	Guillaume Berionni (Supervisor), Johan Wouters (President), Steve Lanners (Jury), Gwilherm EVANO (Jury) & Marc Gingras (Jury)