Carbene‐Stabilized Phosphenium Oxides and Sulfides

Carbene→chalcogenophosphenium adducts, which correspond to an intermolecular stabilization mode of the so far elusive, free oxo‐ and thiooxophosphenium species [R 2 P + = X] (X=O, S) by imidazolylidene (NHC) and diaminocyclopropenylidene (BAC) donors, have been isolated and fully characterized. The dative character of the R 2 C:→P + (X)Ph 2 bond was confirmed experimentally by nucleophilic displacement of the carbene donor with a chloride ion and by an exchange reaction of the NHC ligand of the NHC:→P + (O)Ph 2 adduct with an independently prepared BAC ligand, thereby giving the BAC:→P + (O)Ph 2 adduct. This dative character was further characterized by the DFT‐calculated preference of carbene→chalcogenophosphenium systems for a heterolytic dissociation mode over a homolytic one.