Catalytic reduction of acetophenone with transition metal systems containing chiral bis(oxazolines)

The catalytic behaviour of several Ru, Rh and Ir systems containing bis(oxazoline) ligands (1–6) has been tested in the asymmetric reduction of acetophenone (7) to give 1-phenylethanol (8) by hydrogenation (Ir systems), transfer hydrogenation (Ir and Ru systems) and hydrosilylation (Ir and Rh systems). Ligands 1 and 3 gave good activities, obtaining the best asymmetric induction with Ir–1 system in the hydrosilylation (ee up to 50% (S) of 8). In order to identify the catalytic precursors, Ru (9–11) and Ir (12) complexes were synthesised and characterised. NMR studies of ruthenium complexes showed the existence of two main isomers in a ca. ratio 3/1, in agreement with the PM3(tm) calculations carried out for 10.