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 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.