First experimental evidence for the elusive tetrahedral cations [EP3]+ (E = S, Se, Te) in the condensed phase

Abstract

Condensed phase access to the unprecedented tetrahedral cations [EP₃]⁺ (E = S, Se, Te) was achieved through the reaction of ECl₃[WCA] with white phosphorus ([WCA]⁻ = [Al(OR^F)₄]⁻ and [F(Al(OR^F)₃)₂]⁻; –R^F = –C(CF₃)₃). Previously, [EP₃]⁺ was only known from gas phase MS investigations. By contrast, the reaction of ECl₃[A] with the known P₃³⁻ synthon Na[Nb(ODipp)₃(P₃)] (enabling AsP₃ synthesis), led to formation of P₄. The cations [EP₃]⁺ were characterized by multinuclear NMR spectroscopy in combination with high-level quantum chemical calculations. Their bonding situation is described with several approaches including Atoms in Molecules and Natural Bond Orbital analysis. The first series of well-soluble salts ECl₃[WCA] was synthesized and fully characterized as starting materials for the studies on this elusive class of [EP₃]⁺ cations. Yet, with high [ECl₃]⁺ fluoride ion affinity values between 775 (S), 803 (Se) and 844 (Te) kJ mol⁻¹, well exceeding typical phosphenium ions, these well-soluble ECl₃[WCA] salts could be relevant in view of the renewed interest in strong (also cationic) Lewis acids.