Identification of Suitable Ligands for a Transition Metal-Catalyzed Reaction: Screening of a Modular Ligand Library in the Enantioselective Hydroboration of Styrene

Abstract

Based on a general modular synthetic scheme, a variety of chiral bidentate P/P-, P/S-, P/N-, and P/Se-ligands is accessible in an efficient divergent manner starting from phenol or naphthol derived backbone systems. A library of 20 selected ligands was tested in the Rh-catalyzed asymmetric hydroboration of styrene to give 1-phenylethanol in up to 91% ee after oxidative work-up. It was demonstrated that small variations of the ligand structures lead to pronounced, unpredictable differences in the performance of the in situ generated rhodium complexes. The modular approach should be applicable for the identification and optimization of suitable ligands for other transition metal-catalyzed transformations with comparably low effort.