Protonation of a Xantphos−Phosphole Ligand. Intramolecular Trapping of a P−H Phospholium Salt

Protonation of a bidentate xantphos−phosphole ligand by HBF4 affords only one enantiomer of a cyclic phospholium dihydropholene structure. DFT calculations allowed us to establish that protonation initially takes place at the phosphorus atom of the phosphole moiety to afford a transient P−H phospholium salt, which in turn protonates the CC double bond of the second phosphole unit.