Ruthenium(II) complexes derived from C-2-symmetric ferrocene-based chiral bis(phosphinite) ligands: synthesis and catalytic activity towards the asymmetric reduction of acetophenones

摘要

Chiral secondary alcohols are very important building blocks and valuable synthetic intermediates both in organic synthesis and in the pharmaceutical industry for producing biologically active complex molecules. A series of new chiral Ru-phosphinite complexes (1, 2, 3, 4, 5, 6, 7, 8) were prepared from chiral C-2-symmetric ferrocenyl phosphinites and corresponding chloro complex, [Ru((6)-p-cymene)(-Cl)Cl](2). The complexes were characterized using conventional spectroscopic methods. The binuclear complexes were tested as pre-catalysts and were found to be good pre-catalysts for the asymmetric transfer hydrogenation of substituted acetophenones in basic 2-propanol at 82 degrees C, providing the corresponding optically active alcohols with almost quantitative conversion and modest to high enantioselectivities (46-97%). Amongst the all complexes, complex 6 gave the highest ee of 97% in the reduction of 2-methoxyacetophenone to (S)-1-(2-methoxyphenyl)ethanol at 82 degrees C. Copyright (c) 2015 John Wiley & Sons, Ltd.