Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations

Abstract

[eng] Herein we report the use of polyether binders as regulation agents (RAs) to enhance the enantioselectivity of rhodium-catalyzed transformations. For reactions of diverse substrates mediated by rhodium complexes of the a,w-bisphosphite- polyether ligands 1-5,a-d, the enantiomeric excess (ee) of hydroformylations was increased by up to 82% (substrate: vinyl benzoate, 96% ee), and the ee value of hydrogenations was increased by up to 5% (substrate: N-(1- (naphthalene-1-yl)vinyl)acetamide, 78% ee). The ligand design enabled the regulation of enantioselectivity by generation of an array of catalysts that simultaneously preserve the advantages of a privileged structure in asymmetric catalysis and offer geometrically close catalytic sites. The highest enantioselectivities in the hydroformylation of vinyl acetate with ligand 4b were achieved by using the Rb[B(3,5- (CF3)2C6H3)4] (RbBArF) as the RA. The enantioselective hydrogenation of the substrates 10 required the rhodium catalysts derived from bisphosphites 3a or 4a, either alone or in combination with different RAs (sodium, cesium, or (R,R)- bis(1-phenylethyl)ammonium salts). This design approach was supported by results from computational studies.