Development of catalysts for asymmetric hydrogenation

Abstract

The application of tetradentate aminoalcohol ligands to the KOtBu-catalysed hydrogenation of benzophenone has been studied. Hydrogenation was found to proceed via a transfer hydrogenation process with the ligands acting as hydrogen donors. A series of bidentate and tetradentate ligands containing a variety of coordinating groups including amino, hydroxy, silyl, phosphine and amido functionalities have been prepared and applied to the transition metal-catalysed asymmetric transfer hydrogenation of ketones using iron, ruthenium and rhodium metals although none were found to be enantioselective for the hydrogenation of acetophenone. A series of asymmetric tethered ruthenium half sandwich complexes have been applied to the asymmetric pressure hydrogenation of ketones. Studies have investigated the effect of changing the sulfonamide group, halide and tether length on the activity of the catalysts. The application of an achiral tethered ruthenium half sandwich complex as a catalyst for the pressure hydrogenation of aldehydes is also reported. A novel synthesis of tethered ruthenium complexes using aryl substitution methodology has been developed and applied to the preparation of a series of novel complexes which were found to be highly active for asymmetric pressure hydrogenation of ketones. The application of the synthesis to the preparation of poly(methyl methacrylate) supported complexes is also discussed. Application of the supported catalysts to asymmetric pressure and transfer hydrogenation of acetophenone has shown potential for the development of an active heterogeneous catalyst for transfer hydrogenation of ketones in aqueous media