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

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