thesis
Iron and ruthenium catalysts for asymmetric synthesis
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Abstract
A series of chiral di-, tri- and tetra amine ligands were synthesised from
enantiomerically pure 1,2-cyclohexanediamine and 1,2-diphenylethanediamine and,
in combination with Ru(II) or Fe(II), employed as asymmetric catalysts in the
epoxidation of aromatic alkenes, hydrosilylation of acetophenone, nitro-aldol
reaction and asymmetric transfer hydrogenation (ATH) of different ketones.
A novel class of tridentate ruthenium catalysts of general structure 239 below were
developed. Specifically, a novel class of tridentate ligand was synthesised and a
derivative of (R,R)-N-tosyl-1,2-diphenyl-1,2-ethylenediamine ((R,R)-TsDPEN) and
was found to provide the best activity and selectivity in reduction reactions with
Ru3(CO)12.
Reaction conditions were optimised using 239 for the ruthenium-catalysed ATH of a
number of ketones. In particular, it was found that the presence of meta-methoxy
substituent on the aromatic ring of the substrate yields optimal results under the ATH
conditions employed for 48 h (98% conv., 94% ee). Also, aryl ketones substituted at
the ortho position were reduced in almost quantitative yield, with enantiomeric
excesses greater than 90% in some cases