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

Abstract

Oxidation of diphenylphosphinoferrocene and 1,1′-bis(diphenylphosphino)ferrocene with XeF₂, resulted in the formation of CpFe(η⁵-C₅H₄PF₂Ph₂) 1 and Fe(η⁵-C₅H₄PF₂Ph₂)₂2 respectively. Subsequent reactions with [SiEt₃][B(C₆F₅)₄] yielded [CpFe(η⁵-C₅H₄PFPh₂)][B(C₆F₅)₄] 3 and [Fe(η⁵-C₅H₄PFPh₂)₂] [B(C₆F₅)₄]₂4. PhP(η⁵-C₅H₄)₂Fe 5 was prepared, converted to [PhMeP(η⁵-C₅H₄)₂Fe][O₃SCF₃] 6 and then to [PhMeP(η⁵-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.