Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations.

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 α,ω-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 4 b were achieved by using the Rb[B(3,5-(CF3)2 C6 H3)4] (RbBArF) as the RA. The enantioselective hydrogenation of the substrates 10 required the rhodium catalysts derived from bisphosphites 3 a or 4 a, 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.

Bis(phosphite) ligands with distal regulation: application in rhodium-mediated asymmetric hydroformylations.

Small amounts of achiral polyether binders are employed to enhance the enantioselectivity of the hydroformylation of an array of diversely substituted substrates (increase of up to 62% ee for vinyl acetate) mediated by chiral rhodium complexes derived from the α,ω-bis(phosphite)-polyether ligands 1. To the best of our knowledge, this study represents an unprecedented successful example of the positive regulation of enantioselectivity in hydroformylations.

Allosteric P═O-based receptors for dicarboxylic acids.

The synthesis of new P═O-disubstituted receptors with appended crown ethers and their properties as receptors for dicarboxylic acids have been studied. High affinities have been observed (oxalic and malonic acids with 4-, 5-, 6-, or 8-crown ethers). Binding of a cationic effector within the crown ether unit resulted in a positive "allosteric" effect, which has been determined to be K(rel) = 7 in the best case (binding of malonic acid with Li(+) @ rac-3b).