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

We report here a “nonspectator” behavior for an unsupported L ‐function σ 3 ‐P ligand (i.e. P{N[ o ‐NMe‐C 6 H 4 ] 2 }, 1a ) in complex with the cyclopentadienyliron dicarbonyl cation (Fp + ). Treatment of 1a ⋅Fp + with [(Me 2 N) 3 S][Me 3 SiF 2 ] 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 (Me 2 N) 3 P⋅Fp + (i.e. 1b ⋅Fp + ), which is inert to fluoride addition. These observations establish a nonspectator L/X‐switching in (σ 3 ‐P)–M complexes by reversible access to higher‐coordinate phosphorus ligand fragments.