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 1a^F ?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.