The nature of ruthenium-amino alcohol precursors in the aminoethane (1) coordinates through two nitrogen atoms, was structurally characterised by X-ray diffraction (8). -catalytic cycle of asymmetric hydrogen transfer reactions was studied using two C 2 -symmetrical tetradentate ligands (1 and Based on the results of this study a series of new amino alcohol ligands was synthesised from easily available starting 2) that were synthesised from (nor)ephedrine. The structure of the catalyst precursor was examined through catalysis and materials. Optimisation of the amino alcohol ligand structure resulted in the most effective chiral amino alcohol ligand (5) NMR experiments. It was shown that the active catalyst contains one ligand per metal, which coordinates in a so far that is capable of reducing acetophenone at 0 °C with up to 97% ee in the Ru II -catalysed transfer hydrogenation. didentate N,O fashion (9). In addition, a Ru II Cl 2 complex, in which N,NЈ-bis(2-hydroxy-1-methyl-2-phenylethyl)-1,2-di-From the work of Noyori and co-workers it is clear that [a] Institute of Molecular Chemistry, University of Amsterdam, spectroscopy were used to study the catalyst in situ. The Nieuwe Achtergracht 166, NL-1018 WV Amsterdam, The Netherlands molecular structure of a ruthenium(II) catalyst precursor