Approaches to Novel B-N Chemistry at the Boundary of Frustrated Lewis Pairs and Bifunctional Catalysis

Abstract

This project is devoted to boron chemistry in two ways. Firstly, the development of the boron – nitrogen “Frustrated” Lewis Pairs (FLPs) was investigated by combining the principles of this approach with known bifunctional catalytic methods. This also included design and synthetic efforts towards new bifunctional catalysts 108 and 157 on the basis of L-proline connected to Lewis acidic borane or borinic derivatives, which revealed multiple peculiarities of boron chemistry. Catalyst 176 was successfully utilised in nitro-Michael addition reaction.
Secondly, boronic acids are promising catalysts for the important process of direct amide formation, which is a much more atom efficient and sustainable alternative to the current industrial approaches to amide synthesis. However, the mechanism of action of boronic acids in this process is not yet well understood, while this is crucial for effective design and future application of catalysts for direct amide formation. Thus the roles of both borinic and boronic acids in direct amide formation reactions were investigated. This included isolation of multiple Lewis adducts formed as intermediates or byproducts in different reaction mixtures between amines, carboxylic acids and boron-containing compounds. These results have helped to better understand the reactivity of boron-based catalysts and allowed development of the new mechanistic understanding of boronic acids in direct amide formation.
These finding underlined the complexity of boron-containing systems, the importance of boron-nitrogen Lewis adduct interactions and the high possibility of multiple boron atoms orchestrating the investigated processes.
The non-catalytic thermal direct amide formation reaction was also studied both in flow and microwave reactors in order to better understand these complex multicomponent systems.