First Optically Active Phosphapalladacycle Bearing a Phosphorus Atom in an Axially Chiral Environment

Direct C−H bond activation in the (Sa)-BINOL-derived phosphite (HL) afforded the dimeric cyclopalladated complex (Sa,Sa)-{Pd(η2-L)(μ-Cl)}2 (1), which is the first optically active phosphapalladacycle bearing a phosphorus atom in an axially chiral environment. The ortho-palladated structure of complex 1 was confirmed by spectral (1H and 31P) investigations of mononuclear derivatives and the X-ray diffraction study of the phosphane adduct (η2-L)PdCl(PPh3) (3). The enantiomeric purity of the starting ligand remained unchanged in the PC-palladacycle under the thermal conditions used for the cyclopalladation (∼110 °C); this fact was confirmed by the 31P NMR spectroscopy after chiral derivatization of dimer (Sa,Sa)-1 with the (RC)-valinate auxiliary ligand. The trans(N,C)-configuration of the valinate complex (4) was supported by DFT calculations. The chirality transfer in the new system was discussed on the basis of X-ray diffraction data for the phosphane adduct rac-3 and DFT calculations performed for both mononuclear derivatives.