A Phosphorus Lewis Super Acid: eta(5)-Pentamethylcyclopentadienyl Phosphorus Dication

A Abstraction of chloride from (Cp*PCl2) with the silylium salt [Et3Si][B(C6F5)(4)] afforded [(eta(2)-Cp*)PCl][B(C6F5)(4)] (1), whereas further chloride abstraction using another equivalent [Et3Si][B(C6F5)(4)] was unsuccessful. The corresponding species [(eta(2)-Cp*)PF][B(C6F5)(4)] (2) was derived by fluoride abstraction from (Cp*PF2). Treatment of (Cp*PF2) with 2 equiv of [Et3Si][B(C6F5)(4)] gave [(eta(5)-Cp*)P][B(C6F5)(4)](2) (3), representing an eta(5)-Cp that is bound to phosphorus. 3 behaves as a phosphorus-based Lewis super acid, abstracting fluoride from [SbF6](-) anion with concurrent eta(5)-eta(2)-Cp* rearrangement to give 2. Similarly, the extremely high Lewis acidity and chlorophilicity of 3 is indicated by the equilibration of 3 with Et3SiCl to generate 1 and [Et3Si][B(C6F5)(4)]. The coordination of 2,2'-bipyridine (bipy) to the phosphorus of 3 induces the eta(5)-eta(1)-Cp* rearrangement, leading to a slipped sandwich'' compound [(eta(1)-Cp*)P(bipy)][B(C6F5)(4)](2) (4). 3 also reacts with Et3SiH via eta(5)-sigma-Cp* rearrangement, affording [(sigma-Cp*) PH2SiEt3] [B(C6F5)(4)] (5) and [Et3Si][B(C6F5)(4)].