A Nontrigonal Tricoordinate Phosphorus Ligand Exhibiting Reversible “Nonspectator” L/X‐Switching

We report here a “nonspectator” behavior for an unsupported L‐function σ3‐P ligand (i.e. P{N[o‐NMe‐C6H4]2}, 1a) in complex with the cyclopentadienyliron dicarbonyl cation (Fp+). Treatment of 1a⋅Fp+ with [(Me2N)3S][Me3SiF2] results in fluoride addition to the P‐center, giving the isolable crystalline fluorometallophosphorane 1aF⋅Fp that allows a crystallographic assessment of the variance in the Fe−P bond as a function of P‐coordination number. The nonspectator reactivity of 1a⋅Fp+ is rationalized on the basis of electronic structure arguments and by comparison to trigonal analogue (Me2N)3P⋅Fp+ (i.e. 1b⋅Fp+), which is inert to fluoride addition. These observations establish a nonspectator L/X‐switching in (σ3‐P)–M complexes by reversible access to higher‐coordinate phosphorus ligand fragments. Ein L‐funktionaler dreiwertiger Phosphorligand addiert Fluoridionen durch nukleophile Addition und bildet ein stabiles, isolierbares Metallophosphoran. Die Reaktion ist reversibel. Eigenschaften der Metall‐Phosphor‐Bindung als Funktion der Koordinationszahl an P werden kristallographisch und computergestützt analysiert.