Iron and ruthenium catalysts for asymmetric synthesis

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

Use of tridentate TsDPEN/pyridine ligands in ruthenium-catalysed asymmetric reduction of ketones

A series of enantiomerically pure tridentate ligands based on the 1,2-diphenylethane-1,2-diamine structure, containing additional pyridine groups, was prepared and tested in asymmetric transfer hydrogenation of ketones using Ru3(CO)12 as a metal source. Alcohols were formed in up to 93% ee in the best cases, and good results were obtained with ortho-haloarylketones