Synthesis of a Helical Phosphine and a Catalytic Study of Its Palladium Complex

Abstract

In this study, 9-(diphenylphosphanyl)[7]helicene was prepared as a suitable ligand for the subsequent synthesis of palladium complexes. The corresponding PdL₂Cl₂ complex was then successfully obtained in both racemic and enantiopure forms. The PdL₂Cl₂ complex emerges exclusively in the trans arrangement showing dynamic interconversion between its homo- and heterochiral forms as evidenced by ³¹P NMR. The trans arrangement was ultimately confirmed by X-ray crystallography using single crystals of the homochiral complex. Additionally, the PdL₂Cl₂ complex was subjected to screening of its catalytic activity in a Suzuki-type reaction of aryl bromides with aryl boronic acids showing fair yields of the resulting biaryls. However, the final asymmetric reactions catalyzed by the optically pure PdL₂Cl₂ complex provided targeted binaphtyls only in negligible enantiomeric excess.