New catalysts for amine alkylation reactions promoted by hydrogen borrowing

N-Alkylation of amines with alcohols mediated by borrowing hydrogen is a useful synthetic tool for the preparation of functionalised amines. Specifically, alcohols can be temporarily converted into carbonyl compounds by the metal-catalysed removal of hydrogen. The carbonyl compounds are more reactive than the precursor alcohols and can react in situ with amines to give imines. The metal catalyst returns the borrowed hydrogen to the imines, giving the alkylated amines.

Chapter 1 outlines the potential for the atom-efficient hydrogen borrowing processes, giving an overview of the main transformations that can be carried out using this interesting methodology. A preliminary investigation of the reaction mechanism gave us useful information for the synthesis of more robust catalysts for these processes.

As a result, a new family of rhodium and iridium complexes was synthesised, which contained a modified Cp* ligand bearing an amine on the tethered chain. Two iridium catalysts were found to be the most active among our family of monomeric complexes. More than 20 substrates containing aryl, heteroaryl and alkyl groups were prepared in 62-99% yields; among them, primary and secondary alcohols and primary and secondary amines have been used. Furthermore, a broad range of functional groups were tolerated, such as halides, nitriles, ethers, esters, amides, sulphonamides and carbamates. Furthermore, the development of a recyclable rhodium complex and a chiral iridium catalyst were attempted.

To conclude, Chapter 5 describes the catalytic activities of three dicationic monomers. The N-alkylation of amines on water was explored. The procedure works well for a range of substituted alcohols and amines; in total, 10 compounds have been isolated in good to excellent yield (> 69%).