Electrophilic bis-fluorophosphonium dications: Lewis acid catalysts from diphosphines

Abstract

Stepwise oxidation of 1,8-bis(diphenylphosphino)naphthalene and a series of (oligo)methylene-linked diphosphines with XeF₂ followed by fluoride abstraction yields a family of compounds featuring phosphine, phosphonium and phosphorane moieties in close proximity. The bisphosphonium ions [(C₁₀H₆)(Ph₂PF)₂]²⁺ (5) and [CH₂(Ph₂PF)₂]²⁺ (9a) exhibit remarkable Lewis acidity arising from the proximity of the phosphonium centers. The effectiveness of bisphosphonium dications (5, 9a–e) is examined in a series of Lewis acid catalysed transformations.