New ruthenium catalysts for asymmetric hydrogenation
Abstract
A review on catalytic asymmetric hydrogenation of C=O double bonds is presented in
the first chapter. Noyori’s pioneering research on ruthenium complexes containing both
phosphine and diamine ligands using
[i superscript]PrOH and
[t superscript]BuOK is described, this system gave
impressive highly chemeo-selectivity for C=O bonds and extremely high enantioselectivity
for a range of acetophenone derivatives. Numerous groups have been inspired by Noyori’s
catalyst of the type RuCl₂(chiraldiphosphine)(chiraldiamine), these systems often give
excellent results for acetophenone. However, these catalysts have limitations, they are found
to be either inactive or unselective for hydrogenation of tetralones, dialkylketones, bulky
ketones, some heterocyclic ketones and imines prove difficult using this system.
In this project, we are searching for a new catalyst for asymmetric hydrogenation of
ketones that solve the difficult challenges faced when using Noyori’s
[Ru(diphosphine)(diamine)Cl₂] catalysts system. Departing from Noyori’s type catalyst in the
second chapter is described our effort to synthesise new diamines derived from amino acids
and the synthesis of [Ru(diamine)(diphosphine)Cl₂] complexes. These catalysts are tested in
asymmetric hydrgenation of ketones. In the next two chapters the finding of a new tridentate
P^N^NH₂ type ligand is reported and the novel ruthenium complex containing the tridentate
ligand has been synthesised and characterised by X-ray crystallography and been found to be
active in the hydrogenation of a range of C=O and C=N double bonds, including the
enantioselective hydrogenation of normally unreactive bulky ketones with up to 93 % ee. The
last chapter explains the transfer hydrogenation activity for this new catalyst, involving a
novel method of transfer hydrogenation reaction under microwave irradiation.
Type
Thesis, PhD Doctor of Philosophy
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