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

We report here a nonspectator behavior for an unsupported L-function sigma(3)-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)(3)S][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)(3)P.Fp(+) (i.e. 1b.Fp(+)), which is inert to fluoride addition. These observations establish a nonspectator L/X-switching in (sigma(3)-P)-M complexes by reversible access to higher-coordinate phosphorus ligand fragments.