Pyridinium–phosphonium dications: highly electrophilic phosphorus-based Lewis acid catalysts

Abstract

Using commercially available 2-pyridyldiphenylphosphine (o-NC₅H₄)PPh₂, a family of electrophilic phosphonium cations [(o-NC₅H₄)PFPh₂]⁺ (2) and dications [(o-MeNC₅H₄)PRPh₂]²⁺ (R = F (4); Me (5)) were prepared. The Lewis acidity of these pyridinium–phosphonium dications was probed in Friedel–Crafts dimerization, hydrodefluorination, hydrosilylation, dehydrocoupling and hydrodeoxygenation reactions. The influence of the counterion on the catalytic activity of the electrophilic phosphonium cations is also discussed.