Synthesis and Application of Modular Phosphine-Phosphoramidite Ligands in Asymmetric Hydroformylation: Structure-Selectivity Relationship

A series of hybrid phosphine-phosphoramidite ligands has been designed and synthesized in moderate yields from chiral BINOL (1,1'-bi-2-naphthol) or NOBIN (2-amino-2'-hydroxy-1,1'-binaphthyl). They have achieved highly regio- and enantioselectivities in Rh-catalyzed asymmetric hydroformylations of styrene derivatives (branched/linear ratio up to 56.6, ee up to 99%), vinyl acetate derivatives (up to 98% ee), and allyl cyanide (up to 96% ee). Systematic variation of ligand structure showed that the steric factor on the phsophoramidite moiety determined the performance of the ligand. With the increased hindrance, the branched/linear ratio rose, while the ee value dropped in the hydroformylation of styrene. However, the N-substituents did not influence the selectivities much.