A Nontrigonal Tricoordinate Phosphorus Ligand Exhibiting Reversible "Nonspectator" L/X-Switching.

We report here a "nonspectator" behavior for an unsupported L-function σ -P ligand (i.e. P{N[o-NMe-C H ] }, 1a) in complex with the cyclopentadienyliron dicarbonyl cation (Fp ). Treatment of 1a⋅Fp with [(Me N) S][Me SiF ] results in fluoride addition to the P-center, giving the isolable crystalline fluorometallophosphorane 1a ⋅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 N) P⋅Fp (i.e. 1b⋅Fp ), which is inert to fluoride addition. These observations establish a nonspectator L/X-switching in (σ -P)-M complexes by reversible access to higher-coordinate phosphorus ligand fragments.