Enantiomerically Pure P,N Chelates Based on Phospholene Rings: Palladium Complexes and Catalytic Applications in Allylic Substitution

The synthesis of optically Pure 2-pyridylphospholene ligands by diastereomeric resolution of Pd-II complexes, bearing the corresponding racemic P,N ligand and (R)-alpha-methylbenzylamine, by means of fractional crystallisation is described. A full coordination study of palladium complexes containing 2-pyridylphospholene and the corresponding phosphole ligands, both in solution (by means of NMR spectroscopy) and in the solid state (by X-ray diffraction), was carried out, These ligands were evaluated in Pd-catalysed allylic substitution of racemic substrates (rac-3-acetoxy-1,3-diphenyl-1-propene and rac-3-acetoxy-1-cyclohexene) and (E)-3-acetoxy-1-phenyl-1-propene. A modelling study of the palladium allylic intermediates was performed in order to justify the asymmetric induction observed with the 2-pyridylphospholene ligands. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)