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

Abstract The synthesis of optically pure 2‐pyridylphospholene ligands by diastereomeric resolution of Pd II complexes, bearing the corresponding racemic P,N ligand and ( R )‐α‐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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)