Ferrocenyl-derived electrophilic phosphonium cations (EPCs) as Lewis acid catalysts.

Oxidation of diphenylphosphinoferrocene and 1,1'-bis(diphenylphosphino)ferrocene with XeF2, resulted in the formation of CpFe(η(5)-C5H4PF2Ph2) 1 and Fe(η(5)-C5H4PF2Ph2)22 respectively. Subsequent reactions with [SiEt3][B(C6F5)4] yielded [CpFe(η(5)-C5H4PFPh2)][B(C6F5)4] 3 and [Fe(η(5)-C5H4PFPh2)2] [B(C6F5)4]24. PhP(η(5)-C5H4)2Fe 5 was prepared, converted to [PhMeP(η(5)-C5H4)2Fe][O3SCF3] 6 and then to [PhMeP(η(5)-C5H4)2Fe][B(C6F5)4] 7. The ability of the salts 3, 4 and 7 to catalyze Friedel-Crafts dimerization of 1,1-diphenylethylene, dehydrocoupling of phenol and triethylsilane, deoxygenation of acetophenone and hydrodefluorination of 1-fluoropentane were probed. While compound 7 proved to be ineffective, compounds 3 and 4 were useful Lewis acid catalysts. Compounds 3 and 4 were shown to catalyze the deoxygenation of a series of ketones.