Highlights of the Rh-catalysed asymmetric hydroformylation of alkenes using phosphorus donor ligands

Rhodium is currently the metal of choice to achieve high enantioselectivities in the hydroformylation of a relatively high variety of alkene substrates. The elucidation of the different steps of the catalytic cycle and the characterisation of the resting state, together with the discovery of several types of ligands that are able to provide high enantioselectivities, have made the rhodium-catalysed hydroformylation a synthetically useful tool. For years, ligands containing phosphite moieties such as diphosphites and phosphine–phosphites were considered the most successful ligands to achieve high enantioselectivies in this process. In fact, the phosphite–phosphine BINAPHOS 43 and its derivatives are even today the most successful ligands in terms of selectivity and scope. Recently however, diphosphine derivatives were shown to provide high levels of selectivity. It can consequently be concluded that the key to achieve high enantioselectivities is not the type the phosphorus function involved in the coordination to the metal, but the particular spatial arrangement of the coordinated ligand.