Protonation of a xantphos-phosphole ligand: intramolecular trapping of a P-H phospholium salt

Protonation of a bidentate xantphos-phosphole ligand by [HBF.sub.4] to obtain only one enantiomer of a cyclic phospholium dihydropholene structure is reported. The results from DFT calculations demonstrated that protonation initially took place at the phosphorus atom of the phosphole moiety to obtain a transient P-H phospholium salt, which in turn protonated the C=C double bond of the second phosphole unit.