Cationic P–S–X cages (X=Br, I)

The first condensed‐phase preparation of ternary P–Ch–X cations (Ch=O–Te, X=F–I) is reported: [P 5 S 3 X 2 ] + , [P 5 S 2 X 2 ] + , and [P 4 S 4 X] + (X=Br, I). [P 5 S 3 X 2 ] + is formed from the reaction of the Ag + /PX 3 reagent with P 4 S 3 . The [P 5 S 3 X 2 ] + ions have a structure that is related to P 4 S 5 by replacing PS by P + X and S in the four‐membered ring by P(X). We provide evidence that the active ingredient of the Ag + /PX 3 reagent is the (H 2 CCl 2 )Ag–X–PX 2 + cation. The latter likely reacts with the HOMO of P 4 S 3 in a concerted HOMO–LUMO addition to give the P 5 S 3 X 2 + ion as the first species visible in situ in the low‐temperature 31 P NMR spectrum. The [P 5 S 3 X 2 ] + ions are metastable at −78 °C and disproportionate at slightly higher temperatures to give [P 5 S 2 X 2 ] + and [P 4 S 4 X] + , probably with the extrusion of 1/ n  (PX) n (X=Br, I). All six new cage compounds have been characterized by multinuclear NMR spectroscopy and, in part, by IR or Raman spectroscopy. The [P 5 S 2 X 2 ] + salts have a nortricyclane skeleton and were also characterized by X‐ray crystallography. The structure of the [P 4 S 4 X] + ion is related to that of P 4 S 5 in that the exo ‐cage PS bond is replaced by an isoelectronic P + X moiety.