Organophosphine Oxide/Sulfide-Substituted Lanthanide Binaphtholate Catalysts for Enantioselective Hydroamination/Cyclization

Abstract

A series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands have been prepared ({(R)-H2BINOL-[P(O)R2]2}2-, R = Ph, Et, tBu, 3,5-xylyl, Bn, and OEt; {(R)-H2BINOL-[P(S)Ph2]2}2-). The X-ray crystal structures of (R)-H2BINOL-[P(O)R2]2 (R = Ph, Et, and tBu) evidence the varying binaphtholate dihedral angles and conformational flexibility possible for these ligands. Precatalysts for enantioselective intramolecular aminoalkene hydroamination/cyclization are conveniently generated in situ from the metal homoleptic dialkylamido precursors Ln[N(SiMe3)2]3 (Ln = La, Nd, Sm, Y, Lu, and Sc) and the above binaphthols. The crystal structure of La2{(R)-BINOL-[P(O)Ph2]2}3 reveals strong coordination of lanthanide ion by the phosphine oxide moieties. Enantioselectivities as high as 65% ee for the hydroamination/cyclization of 2,2-dimethylpent-4-enylamine are obtained with {(R)-BINOL-[P(O)Et2]2}NdN(SiMe3)2 at room temperature. Lanthanide catalysts having varying organophosphine oxide-substituted binaph...