Samarium-Catalyzed Diastereoselective Double Addition of Phenylphosphine to Imines and Mechanistic Studies by DFT Calculations
Résumé
The catalytic hydrophosphination of imines represents the most straightforward and atom-economical strategy for the preparation of alpha-aminophosphines, which are useful as biologically active molecules and ligands for catalysis. The first catalytic protocol for the rapid and high-yielding hydrophosphination of common imines enabled by an ene-diamido samarium methoxide catalyst was developed. The reaction allowed the efficient and diastereoselective synthesis of various bis(alpha-amino)phosphines through the double addition of PhPH2 to common imines. The catalytic reaction has a relatively wide substrate scope and offers high diastereoselectivities (up to 99: 1 dr for meso products) and high yields (up to 97%). DFT calculations disclosed an inner-sphere mechanism involving unprecedented activation of a Sm-O bond by a phosphine and stabilization of the addition intermediates by the metal center.