LiCl-effect on asymmetric intramolecular hydroamination catalyzed by binaphthylamido yttrium complexes

Abstract

Chiral alkyl or amido yttrium complexes were prepared from N-silyl- or N-cyclopentyl-substituted binaphthylamido ligands. According to the synthetic procedure, these complexes could be obtained in their neutral form or as heterobimetallic complexes in the presence of 1 equiv. LiCl. These new species were characterized by IR and NMR spectroscopies, elemental analyses and some of them by X-ray diffraction studies. Their efficiency as catalysts for the asymmetric intramolecular hydroamination was then evaluated with several substrates towards the synthesis of two pyrrolidines and a piperidine derivative. A cooperative effect between the lithium and the yttrium atoms was undoubtedly revealed. LiCl-containing complexes afforded indeed higher enantioselectivities than their salt-free counterparts and according to the structure of the chiral ligand, they were also the most active species.