New C2-symmetrical ferrocenyl diamines as ligands for ruthenium catalyzed transfer hydrogenation

The new C-2-symmetrical ferrocenyl diamines 5-7 and 13 proved to be good ligands for the ruthenium catalyzed enantioselective transfer hydrogenation of unsymmetrical ketones. The stereocontrolled and highly flexible synthetic route to the new diamines made it possible to vary the ligand structure in an efficient manner. A short trial and error process led to a very active catalytic system with diamine 6a as the ligand, which is capable of reducing ketones even at -30 degrees C using 2-propanol as a hydrogen source. Enantioselectivities up to 90% were reached in the reduction of 1'-acetonaphthone. (C) 1998 Elsevier Science Ltd. All rights reserved.