Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations

Abstract

<p> 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 <strong>1</strong><strong>-</strong><strong>5,a</strong><strong>-</strong><strong>d</strong>, the enantiomeric excess (<em>ee)</em> of hydroformylations was increased by up to 82% (substrate: vinyl benzoate, 96% <em>ee</em>), and the <em>ee</em> value of hydrogenations was increased by up to 5% (substrate: <em>N</em>-(1-(naphthalene-1-yl)vinyl)acetamide, 78% <em>ee</em>). 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 <strong>4b</strong> were achieved by using the Rb[B(3,5-(CF₃)₂C₆H₃)₄(RbBArF) as the RA. The enantioselective hydrogenation of the substrates <strong>10</strong> required the rhodium catalysts derived from bisphosphites <strong>3a</strong> or <strong>4a</strong>, either alone or in combination with different RAs (sodium, cesium or (<em>R</em>,<em>R</em>)-bis(1-phenylethyl)ammonium salts). This design approach was supported by results from computational studies.</p>