Tetraphosphacubane chemistry: Probing phosphorus reactivity by protonation, alkylation, and alkynylation. Formation of novel phosphonium Di- and monocations in superacid media and monocations with super electrophiles

Tetra-tert-butyltetraphosphacubane (1) is diprotonated with FSO 3 H-SbF 5 (1:1) (Magic acid)/SO 2 at two of the four equivalent phosphorus atoms to give a persistent diphosphonium cation 2. In FSO 3 H/SO 2 or CF 3 SO 3 H (TfOH)/SO 2 only the monoprotonated phosphonium ion 4 was observed. Upon exothermic quenching of the Magic acid solutions of 2 apart from intact 1, oxotetraphosphacubane 3 was formed. Quenching of the FSO 3 H or TfOH solutions of 4 (no SbF 5 ) gave intact 1 together with traces of 3. Ambient reactions of 1 with methyl triflate, trimethyloxonium tetrafluoroborate and (trimethylsilyl)methyl triflate led to monoalkylation at phosphorus. Reaction of 1 with propene/TfOH as an i Pr + source gave the monocation 8 ( 13 P NMR) in competition with extensive olefin oligomerization. Crowded triisopropyl triflate did not react with 1 even under forcing conditions. Similar reactions of 1 with alkynyl(phenyl)iodonium triflates led to monoalkylation at phosphorus