Resolution of β-aminophosphines with chiral cyclopalladated complexes

Resolution of the racemic chiral β-aminophosphines Ph2PCH2CH(Ph)NH(Ar) (L1 for Ar = C6H5 and L2 for Ar = 2,6-C6H3iPr2) has been investigated by use of different cyclopalladated complexes as chiral agents. The resulting complexes afford diastereomeric adducts in a 1:1 ratio. After successive crystallizations from ethanol, a d.e. of 98% was achieved for one aminophosphine palladium complex, while no significant d.e. was obtained after crystallizations from chlorinated solvents. The X-ray structure analysis has pointed out intermolecular hydrogen interactions N–H⋯Cl between the P,N ligand and the chloride ion, which are responsible for the formation and stabilization of the diastereomeric adducts. Thus, the use of oxygenated solvents cancels such hydrogen interactions by their stronger donor character and makes the diastereomers separation possible, allowing to isolate the optically pure (R)-Ph2PCH2CH(Ph)NH(Ph) L1 of which the absolute configuration has been determined from the X-ray structure analysis of the related palladium dichloride complex.