First optically active PC-palladacycle bearing a phosphorus atom in an axially chiral environment

Abstract

Direct aromatic C—H bond activation in the (Sa)-BINOL-derived phosphite (Sa)-HL afforded the dimeric cyclopalladated complex (Sa,Sa)-{Pd(η2-L)(μ-Cl)}2 (2) which is the first optically active PC-palladacycle bearing a phosphorus atom in an axially chiral environment. ortho-Palladated structure of dimer 2 was confirmed by spectral (1H and 31P NMR) examination of its mononuclear derivatives and by X-ray diffraction analysis of the phosphine adduct (η2-L)PdCl(PPh3) (4). 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 in situ of dimer (Sa,Sa)-2 with the (RC)-valinate chiral auxiliary (Val). trans(N,C)-Configuration of the valinate complex (η2-L)Pd(Val) (5) was established by 1H NMR and supported by DFT calculations. The chirality transfer in the new PC-palladacycle was discussed on the basis of X-ray diffraction data for the phosphine adduct rac-4 and DFT calculations performed for both phosphine and valinate mononuclear derivatives.