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

In this study, 9-(diphenylphosphanyl)[7]helicene was prepared as a suitable ligand for the subsequent synthesis of palladium complexes. The corresponding PdLCl complex was then successfully obtained in both racemic and enantiopure forms. The PdLCl complex emerges exclusively in the arrangement showing dynamic interconversion between its homo- and heterochiral forms as evidenced by P NMR. The arrangement was ultimately confirmed by X-ray crystallography using single crystals of the homochiral complex. Additionally, the PdLCl 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 PdLCl complex provided targeted binaphtyls only in negligible enantiomeric excess.