From Phosphidic to Phosphonium? Umpolung of the P -Bonding Situation in [CpFe(CO)(L)(η -P )] Cations (L=CO or PPh ).

Upon coordinating P to electron poor cyclopentadienyl-iron cations, the average P-P bond distances shrink and the respective P breathing mode in the Raman spectra (600 cm , P ) is blueshifted by >40 cm in [CpFe(CO)(L)(η -P )] cations (L=CO or PPh ). Analysis suggests that this corresponds to an umpolung of the bonding from more phosphidic in the known, electron-rich systems to more phosphonium-like in the reported electron-poor versions. This may open new functionalization pathways for white phosphorus P .